this Neither doth the weight of the 28 ounces of Mercury D E burden the Ballance but only 28 ounces of the Water E F. Neither doth the Ballance support the weight of the 42 ounces of Mercury G H but it is only burdened with 42 ounces of the Water H I. The reason is most evident because according to the Principles of the Hydrostaticks already laid down the Cylinder of Mercury A B within the Tub A B rests immediatly upon the imaginary surface of the Water A D G and therefore cannot burden the scale in any wise The same is true of the other two Cylinders of Mercury But in this I find small difficulty The greater is how to make it out that the scale K supports 14 ounces of the Water B C and 28 of the Water E F and 42 of the Water H I. To make this seem probable consider first as was noted that this VVater is 15 foot deep and consequently the Pillar of VVater B C 13 foot 10 inches The VVater E F 12 foot eight inches And H I 11 foot and a half Consider secondly though this be true yet we must count the Pillar of VVater Z M 49 foot high The reason is evident because the Pressure of the Air upon the surface of all Waters according to the 25 Theorem is equivalent to 34 foot of Water this then being added to 15 makes 49 and by this reckoning the Water B C is 47 foot ten inches the Water E F 46 foot eight inches And lastly the Water H I 45 foot six inches Thirdly for easie counting I must suppose the whole Cylinder Z M to weigh 42 ounces every 14 inches one ounce and consequently the Water B C to weigh 41 ounces the Water E F to weigh 40 ounces the Water H I 39 ounces Note that in Physical demonstrations 't is not needful to use Mathematical strictness in counting and so leaving out fractions we shall onely use round numbers Consider fourthly that in all Fluids as hath been frequently marked there is a pondus and potentia the Water B C being the pondus and the Mercury A B the potentia the one striving to press down the Tub the other striving to press it up Consider fifthly that by how much the more a Body suspended in a Fluid is pressed up by so much the less the weight that presseth it down is foâ—nd and contrariwise by how much the less it is pressed up by so much the more the Pressure above is found Consider sixthly the less that a surface of Water is burdened the more able it is to counterballance the opposite Pressure and the more it is burdened it is the less able Consider seventhly that the Mercury A B which is evident in all Fluids not only presseth downward and burdens the surface A D G but also presseth upward and therefore actually endeavours to thâ—ust up the Tub and so it is that the Tub is pressed between two namely between the Water C B and the Mercury within it Now from these considerations I say the scale K must support and bear up 14 ounce of the Water B C for seing the Mercury is supported by the surface of VVater on which it rests it cannot by any means burden the ballance with its weight and seing it actually presseth up the Tub according to the seventh consideration it must so much the more counterpoise according to the sixth the opposite Pressure of the VVater B C and consequently diminish the weight of it so that the Ballance cannot support the whole but a part For according to what degrees of force the Mercury presseth up the Tub with according to the same must the Pressure upon the top of the Tub be diminished and so if the Mercury press up the Tub with the force of 27 ounce the VVater B C must press it down with 14 ounce only and so the Cylinder B C that weighs really 41 ounce must press the top of this Tub only with 14 which 14 ounce really counterpoiseth the 14 ounce of Stone in the Scale L. But how is it made out that the Mercury A B presseth up with 27 ounce For understanding this remember that the VVater is 49 foot high taking in the Pressure of the Air and that a VVater of that deepness is able to support 41 inches of Mercury every inch weighing one ounce For if 14 of Water be able to support one of Mercury 49 foot or 567 inches must support 41. If then the part of the surface A be able to weigh 41 it must have of upward Pressure 27 ounces seing it's counterpoised de facto only with 14. Take notice that in the Hydrostaticks the word pressing or weighing as really and truly signifies a weighing up as a weighing down seing it is no less essential to Fluid Bodies to move upward than downward and that with equal force and weight According to this reasoning the Ballance supports 28 ounces of the Water E F Imagine the second Tub to be suspended as the first seing the Cylinder of Mercury D E presseth up the Tub only with the weight of 12 ounce which 28 ounce really counterpoiseth the 28 ounce of Stone in the Scale L. But why doth the Mercury A B press up with 27 ounce and the Mercury D E with 12 For answer remember according to the sixth consideration the shorter a Cylinder of Mercury is the surface upon which it rests is the stronger and more able to press it up and contrariwise the longer it is the surface is the more unable and weak therefore A B being shorter and lighter than D E the surface of Water must press it up with greater force so that if the said surface A M be able to press up the Mercury A B with 27 ounce it must press up the Mercury D E only with 12 ounce According to this rule if the Mercury A B were 15 inches high it would press up only with 26 ounce if it were 16 with 25 if 17 with 24 if 18 with 23 and so forward This leads us to a clear discovery of all the secrets here for if the Mercury A B thrust up the Pipe with the weight of 27 ounce then must the Scale K be eased of so much weight and so much must be subtracted from L. Now let us imagine the Pipe A B to be empty both of Air Water and Mercury in this case 41 ounce must be in the Scale L to counterpoise it seing the whole Cylinder B C that weighs so much does now really counterpoise it Let us imagine next these 14 inches of Mercury to rise and fill the Tub A B in this case there happens a great alteration because the rising of them are really equivalent to the subtracting of 27 ounce from the Scale L and the reason is because by so rising and filling the Tub they thrust up the said Tub and by this means easeth the Scale K of so much weight Now this Scale being eased you must of necessity
not one part of the mans body that weighs within the Ark or makes it heavier Yet I affirm that when the mans body is within the Ark a less weight will sink it then when his body is out of it even as much less than before as is the just weight of the one half of the man For example if 1680 pound be the just counterpoise of it without the Man then after the Man is in it it will take only 1568 pound to counterballance it supposing the one half of the man to weigh 112 pound or seven stone yet it is not the weight of the man that makes this difference For understanding what 's the cause of this alteration consider that when a mans body is within the Ark there is less Air in it then while his body is out of it even as much less in quantity as the bulk of the parts are that are within If this be then must the Ark become heavier not because the mans body makes it heavier but because there is less Air in the Ark then before and therefore there arises an inequality between the weight of the foot-stool and the weight or rather lightness of the Ark. For if 1680 pound of Lead was the just counterballance of it when it had 30 cubique foot of Air within it it must exceed when there is less Air in it But there occures here two difficulties the first is what 's the reason why as much weight must be deduced from the foot-stool as is the the precise weight of the one half of the man Secondly how shall we come to the true knowledge of that weight that is to know distinctly how many pounds or ounces it is of For answer let us suppose that the one half of the man is just as heavy as so much Water equal in bulk to his own half This may be granted without scruple seing a mans body is judged to be of the same specifick and natural weight with Water and though there should be some small difference yet it will not make or produce any insufficiency in the argument for these demonstrations are not Mathematical but Physical Therefore as much Water in bulk as is equal to that part of the man that is within the Ark must be as heavy as the half of the man Now supposing the half of the man to weigh 112 pound and consequently that Water to weigh as much I affirm the said Water to contain 3456 cubique inches but 3456 cubique inches makes exactly two cubique feet which I gather thus Seven pound of Water requires 216 cubique inches because a Cube of six inches weighs exactly seven pound therefore according to the rule of proportion 112 pound will require 3456 inches which amounts to two cubique foot The Ark then by receiving the one half of the mans body loseth two cubique foot of Air therefore if 30 foot of Air require 1680 pound weight of Lead to counterpoise it 28 foot of Air must require only 1568 pound therefore to make a new counterballance you must deduce 112 pound from the foot-stool This answers both the difficulties If it be said that the foot-stool weighs less in VVater than in Air therefore it must be heavier then 1680 pound I answer 't is needful to abstract from that difference till the just calculation be once made and that being now done I say that a Cube of Lead 16 inches weighing 1680 pound If Lead be 13 times heavier than VVater will lose about 130 pound The reason is evident because a heavy body weighs as much less in VVater than in Air as is the weight of the Water it expells But so it is that a Cube of Lead of 16 inches expells a Cube of VVater 16 inches But a Cube of VVater 16 inches weighs 130 pound which I gather thus 216 inches or a Cube of six inches weighs seven pound therefore 4032 inches must weigh 130 pound For if 216 give 7,4032 must give 130. But to return Though there be small difficulty to let it down and to sink it 20 or 30 fathom yet there is no small difficulty to pull it up again And the reason is this because the further down it goes the Air within is the more contracted and thrust up by the Pressure of the Water towards the roof By this means though near the top of the Water there was little difference between the weight of the Lead and the Ark yet 9 or 10 fathom down the difference is great the weight of the one far exceeding the weight of the other and therefore there must be greater difficulty to pull it up from 10 fathom than from 5 and yet more difficulty from 20 than from 10. However yet 't is observable that as the Ark in going down becomes heavier and heavier so in coming up it growes lighter and lighter therefore less strength is required in pulling it up from the tenth to the fifth fathom than from the fifteenth to the tenth the reason is because in coming up the Air within expands it self and fills more space in the Ark which in effect makes it lighter and more able to overcome the weight of the Lead To make these things more evident let us suppose that when the Ark is down 18 or 20 fathom the Air to be contracted by the force of the Water from L M to P Q 12 inches Next that the weight of the foot-stool is 1680 pound Now if this weight was the just counterpoise of the Ark at the top of the Water then surely it must far exceed it now when it 's 20 fathom down because the Air that was 30 foot is now reduced to 21. Count then and you will find that if 30 require 1680 21 will only require 1176 therefore the weight of the Lead will exceed the weight of the Ark at 20 fathom deep by 504 pound This will be yet more evident if we consider that while the top of the Ark E F G H is level with the surface above the VVater thrust out of ' its own place by this bulk is just the weight of both Lead and Ark. But when ' its down 20 fathom and the Air reduced from L M to P Q there cannot be so much VVater expelled now as before seing the space L M P Q is full of VVater Now I say the Lead at 20 fathom must be exactly so much heavier than the Ark as is the weight of the said VVater L M P Q which in effect will be 504. pound for ' its a square body 36 inches in thickness and 12 in deepness The weight of the rope is likewise to be considered that lets down the Ark for the longer it be and more of it goes out it 's the heavier and more troublesome to pull up There is no way to cure this difficulty but by finding out a way how to keep a just counterpoise between the Lead and the Ark all the time it is in going down If the Air within did
age having rejected the old opinion of the earths nourishing of Plants or being converted into their aliment have made many laudable Experiments for finding out the materials and means of their growth and vegetation such as Sir Francis Bacon's Observe of Germination Helmonts of a Willow and the Noble Mr. Boyl's of a Gourd c. For though a Tree be cut down and the root thereof wax old in the earth and the stock die in the ground yet through the sent of Water it will bud as Iob speaketh Chap. 14. 7 8 9. I shall add a short remark of a Willow growing without earth Upon the 13 of April 1662 I set a top branch of the Peach-leaf'd Willow in a Glass-viol among 12 ounces of pure Spring Water with three small buds upon the top thereof scarce yet discernable The first ten or twelve dayes little white specks appeared upon the sides of the Willow like small drops of Quick-silver or like the first Bubbles that arise upon the fermentation of Ale or Wine but no consumption of the Water all this time Indeed the Gemms which stood three inches above the Water did visibly swell about the twelfth day About the fifteenth day I perceived small white roots within the Water upon several places of the Plant and observed the Liquor grow somewhat thick and decay in bulk considerably Having perceived this I took another Glass of the same bigness with that wherein the Willow grew and having filled both top-full with Spring Water I observed clearly the consumption of the Water wherein the Plant stood to be so great that during May Iune and a great part of Iuly every week at least an ounce and an half or two ounces of it were insensibly spent whereas the other Water standing by in an open Vessel of the same size made not waste of one spoonful in a whole moneth About the middle of August the Water turned very thick and green like that whereon Duck-weed useth to grow and the fair white roots were all obscured from the sight although the Vessel by the multitude of roots was not capable of the third part of Water it received at first At this time the branches were advanced to half the bigness and a much greater length than the whole stock at its first planting and the leaves of as fresh a verdure as any Willow in the fields Thus having observed that a tree of four ounces weight could in three moneths time and little more consume insensibly seven or eight times its own weight of pure Water without the warm preservation of the earth and by its own proper digestion to thicken the remnant of the Water that it might serve for lorication of the tender fibres of the roots I took the Glass the Tree and all and threw them over a Window supposing it needless to recruit the Water any more and judging it impossible without the warm guard of the earth that the naked Tree could be preserved in Winter yet it had the good fortune to fall among some thick Herbs in the corner of a little Garden where after it had lien all Winter it was found and brought back to me the branches fairly budding in April the whole Tree fresh and green yet very little Water was left in the Glass by reason as I judged it had fallen upon its side Then I endeavoured to keep Water about it but the Stock filling the neck of the Viol and the Roots the whole body thereof the starved Plant died in May after it had lived a whole year without earth From this it would seem that this kind of Tree and it may be many moe doth dissipat insensibly six times more Liquor than it doth assimilar and by consequence that a great quantity of moisture is necessary for maintainance of great Woods Neither is there any way so advantagious for draining moist ground where there are no living Springs as that of planting abundance of Timber which will best agree with that kind of soyl for by this means what was formerly noisome and superfluous is now converted partly into the useful aliment of the Timber and partly sent abroad in insensible exhalations which according to the nature of the emitting Plants prove either very noisome or wholsome to the Neighbour-Inhabitants Great care therefore would be had in the choise of such Trees as are to be planted in such moist ground as are near to mens dwellings or places of concurse They are not fools who prefer Firs and Lime-trees in their Avenues to Oak and Elme Let the effects of the Atomical exhalations of Alder and Oak upon fine Linnen and white Skins be more particularly noticed Having spoken somewhat of the aliment and growth of Plants I shall in the next place give a short hint at the motion of their aliment especially of Trees That the alimentary juice of Plants is much thinner than that of Animals no man I suppose will deny seing that is conveyed thorow the trunck or body of the Plants by inperceptible pores but this for the most part is sent thorow all the members through patent and manifest Vessels But how the nourishing and vital juice in Plants doth move and by what passages hath not yet been made known by any that I have seen I made once a few Observations for trying of the motion of the aliment of Trees which bred in me this conjecture The nutritive juice of Trees is transmitted both to the roots and branches through the heart or pitch and woody pores of the Timber and when it is come to the extream parts it returns again from the tops of the roots and branches between the bark and timber into these forenamed interior passages and so back to the extremities again and that continually so long as the life remains And because the substance of that skin or bark which invests the fibres of the root is more open and porous than that which is upon the outward branches therefore it seems that so much as is superadded to the stock of the former aliment from the earth is conveyed to the heart and pitch by means of and together with that part of the retrograd juice which returns from nourishing and enlivening the timber of the root-branches for it is an easie Experiment to make the top of any Tree become root by laying it down and receives the impressions of the life of the Tree common to the whole mass of alimentary juice like the I hyll in Animals mixed with the blood of the Veni-cave before it come to the heart This motion is not to be thought alwayes alike swift or of equal celerity for the vital juice of the Tree becomes so thick and oleagenous in the Winter that the motion thereof to the outward is scarce discernable though the preparation of the Gemmes both for leaves and flowers are observed by the curious and can be distinguished even in the coldest seasons and the returns inward are in so small quantities that they are rather like
Mercury and with the weight of 41 ounce of VVater so much the VVater B C weighs which is 55 ounce but a surface that hath only the Potentia of 42 can never support a Pondus of 55 no not of 43. It may be objected thus Put the case a Cylinder of Gold or Brass were suspended in this VVater as the Pipe and Mercury G H are suspended by the Ballance would not the Ballance support the whole weight of it without supporting any part of the weight of the VVater I H that rests upon the top of it I answer there 's a great difference between the two because a Cylinder of Gold or Brass suffers both the upward and downward Pressure of the VVater but the Mercury G H suffers only the upward Pressure being freed of the downward by the top of the Tub. From this Experiment of letting in the VVater upon the top of the Mercury we see first that when two Fluids are in equilibrio one with another a very small weight will cast and turn the Scales because if the sixth part of an inch of VVater come in at Q it presently alters the hight of the Mercury from 42 inches to less Secondly 't is impossible for a surface of Water to support more weight than its own proper burden because the part S cannot support more no not a grain than 42 ounce VVe see thirdly that it is as impossible for a surface of VVater to support less than its own burden because whatever loss of weight the Pillar of Mercury S Q suffers by the ingress of the VVater Q O it s made up again by the same VVater If it be objected that the 14 inches of VVater Q O are not so heavy by far as the 14 inches of Mercury that fell down I answer its true yet the part S is as much burdened as before because what is wanting in weight it s made up and compensed by Pressure VVe see fourthly that the Pressure of a Fluid is a thing really distinct from the natural weight according to the 22 Theorem because though the 14 inches of Water Q O are not so heavy naturally as the 14 inches of Mercury that fell down yet the Pressure of them upon the surface S is as much We see fifthly that 14 inches of Water that 's â— body fourteen times lighter than Mercury may have as much weight with them as 14 ounce of Mercury We see sixthly that a Cylinder of Mercury cannot be suspended in Air or in Water unless it be guarded with a Tub to preserve it from the downward Pressure of that Air or Water for by opening an hole in Q the Meâ—cury subsides We see seventhly that 't is impossible 〈…〉 Fluids to suspend one another mutually unless there be a sort of equipondium between them because no sooner you destroy the equipondium between the 42 inches of Mercury Q S and the part of the surface S by the ingress of the Water Q O but assoon there ariseth a new one We see eighthly as we noted before the nearer a Body comes to be equally pressed with a Fluid the less is the Pressure of that Fluid sensible because less weight is required in the Ballance to counterpoise the Pressure and weight of the Water R Q after the ingress of the Water Q O P than after the ingress of the Water Q O. We see ninthly that when a Body is equally and uniformly preâ—â—ed with a Fluid the Pressure is insensible because after the Water hath thrust down all the Mercury from Q to S there 's no more weight at all of the Water R Q found in the Ballance We see tenthly that not only in Water the Pressure of Water may be found but out of it namely in the Air as is clear from the Ballance that supports the Pressure of the Water R Q. We see eleventhly a ground to distinguish between the natural Ballance and the artificial Ballance The artificial Ballance is the Ballance K L the natural is the Pipe Q S. We see twelfthly that they keep a correspondence between themselves or some Analogy for by what proportion the Water thrusts down the Mercury by that same proportion the pondus L of the Ballance is lessened and by what proportion the Mercury rises in the Pipe by that same is the weight L augmented in the Scale We may subjoyn lastly that the easiest way of explicating the Phenomena of Nature is not always the best and truest For some may think it were far easier to say that the Ballance supports the Mercury A B or D E and not any part of the Water B C or E F. But such a way would be false and absurd and contrary to all the former Doctrine EXPERIMENT XII Figure 16. THis Schematism represents a Water 100 foot deep whose first and visible surface is I H K. And L M is the ground of it C D is a piece of brass 30 inches high and 12 inches in diameter suspended upon the imaginary surface of Water A N B which is distant from the top I H K 25 foot This Brass cannot go farder down when demitted from H because it 's keeped up by the Force and Pressure of the surface of Water A N B which I prove thus The part B sustains de facto a Pillar of Water K B 1400 pound weight therefore the part N is able to sustain as much I suppose here the said piece of Brass to weigh 1400 pound The Water K B is 1400 pound because its a Pillar 25 foot high and 12 inches thick for one cubical foot weighs 56 pound Trois The connexion of the argument is evident because it is as easie for a surface of Water to sustain a solid Body as to sustain a Fluid Body therefore if the part B support the Fluid Pillar K B the part N must be able to support likewise the solid Pillar C D which is of the same weight Iâ— it be objected that the part N sustains besides the Brass C D a Pillar of Water E F 22 foot high and a half which two will weigh 2260 pound I answer upon supposition that neither Water nor Air succeeded the space E F being void of both the Brass would be suspended with the force and power of the Water N. And though this cannot be made practicable yet the Theory of it may conduce much for explicating the secrets and mysteries of the Hydrostaticks But why ought the Brass to be suspended at 25 foot from the top I answer because the potentia of the surface A N B is equal to the pondus of the Brass To evidence this consider that Brass is a Body naturally heavier then Water I shall suppose ten times that 's to say one inch of Brass will counterpoise ten inches of Water If this inequality be then must this Pillar of Brass go so much farder down than the first surface I H K as the one is heavier in specie or naturally than the other therefore it
must sink 25 foot exactly seing a piece of Brass 30 inches high requires 400 inches of Water or 25 foot to counterpoise it for if one inch of Brass require ten inches of Water then surely 30 inches must require 300. Yet it is no matter what the thickness be provided it be no higher than 30 inches To advance some farder let us make a second supposition namely while the Brass is thus suspended upon the surface A N B suppose the Air to come down and fill up the imaginary space E F then must the Brass be thrust down as far as the surface O P that 's 34 foot below the surface A N D and 59 from the top The reason of it is this because the weight of the Air superadded is equivalent to the Pressure of a Pillar of Mercury 29 inches high and 12 inches thick therefore the Brass being burdened with this it must go so farder down till it meet with a surface whose potentia is equal in weight to the pondus of both which is precisely 59 foot from the top for if one inch of Mercury require 14 of Water then 29 inches must require 405 inches or 34 foot In a word it must go as far down as that surface that sustains a Pillar of Water that would counterpoise in a Ballance the Brass C D and a Pillar of Mercury 29 inches high and 12 inches thick both which weighs 3290 pound From what is said we see first that of two heavy bodies differing in weight the lighter may go further down than the heavier This is clear because a slender Cylinder of Gold in form of an Arrow half an inch thick and 28 inches long weighing 28 pound 't is no matter though the just weight of it be not determined will go down 35 foot in Water before it meet with a surface whose potentia is equal in weight to its own pondus for if Gold be 15 times heavier naturally than Water then the said Cylinder must go down before it rest 420 inches or 35 foot But a piece of Gold 12 inches long and six inches thick that perhaps will weigh 208 pound will sink no further than 15 foot And the reason is because if one inch of Gold require 15 of VVater to counterpoise it then 12 must only require 180 or 15 foot Note that both the bodies must go down Perpendicularly and not as it were Horizontally with their sides downmost for if they go down after this manner they cannot sink so far The reason of this is also evident because a heavy body goes so far down and no further till it hath thrust â—s much Water out of its place as will counterpoise it self in a Ballance That 's to say if an heavy body weigh 100 pound it must go no further down than after it hath thrust out 100 pound of Water But so it is that a piece of Gold in form of an Arrow going down side-wise or with the two ends parallel to the Horizon will thrust as much Water out of its place as will be the weight of it self before it can go down 15 or 16 inches from the top because for every inch it goes down side-wise it expellâ— 28 inches of Water In going down two inches it expells 56. In going down three inches it expells 84 and so forward till it go down 15 inches where it expells 420 inches but 420 inches amounts to 35 foot Now take a Cylinder of Water 35 foot high and just the thickness of the Cylinder of Gold which I supposed to be of half an inch and put them in a ballance and you will find the one just the weight of the other Neither can the piece of Gold go so far down as before if it go down side-wise because for every six inches it is drowned it expells a bulk of Water 12 inches long and six inches thick therefore it must be suspended before it go beyond 90 inches or seven foot and an half now if six inches give one foot 90 inches will give 15 foot but 15 of Water in hight and six inches thick is the just weight of it in a ballance viz. 208 pound We see secondly the broader and larger the surface of a Fluid be 't is the more able and strong to support an heavy burden therefore the part of a surface of Water six inches square every way will carry a far greater weight than a part four inches square Though a surface of Water 34 or 35 foot deep be not able to sustain a Cylinder of Gold if it exceed 28 or 29 inches in hight yet take a Cylinder of Gold 10 foot high and reduce it by making it thicker to the hight of 20 inches a surface of Water little more than 24 foot deep will sustain it Or reduce a Cylinder 10 foot high which requires a surface more than 100 foot deep to a Cylinder six inches high a surface little more than seven foot deep will support it We see thirdly the reason why bodies that are broad and large move â—lowlier through Air and VVater than bodies that are more thin and slender though both be of the same weight in a ballance For example 20 pound of Lead long and slender like an Arrow will go sooner to the ground of a deep VVater than a piece of Lead of the same weight in form of a Platter or Bason The reason is because as the body is broader so it takes a broader part of a surface which broader part is stronger and abler than a narrower part and so makes the greater resistance The same is the reason why a Bullet six inches in Diameter moves â—lowlier thorow the Air shot from a Cannon than a Bullet one inch in Diameter For the same reason Ships of seven or eight hundred Tun move far slowlier thorow the Air and Water than Vessels of less burden Item large and big Fowls as Eagles move slowlier than small Birds as Swallows Yea of Fowls of the same quantity one may move quicklier than another as is evident in long-wing'd Hawks as Falcons that by the sharpness of their Wings move far more space in half an hour than Kites or Gose-Hawks whose wings are rounder We see fourthly that there 's no body how heavy soever but it may be supported by the surface of a Fluid either in Air or in VVater I grant the strongest surface of Air that can be had is not able to support more weight than a Cylinder of Gold 28 inches high yet though it were as large and broad as a Mill-stone if it do not exceed the said hight the Air is able to sustain it For the same cause if it were possible to free a Mill-stone of the Air that rests upon it the Air below would lift it from the ground and carry it up many fathoms even till it came to a surface equal in power to the weight of the Stone Or if a large Mill-stone were demitted from the top of the Atmosphere towards the Earth it could hardly
string the other end being fastened to a Ballance in the Air gravitats and weighs down the Scale and the reason is because Lead and Gold are naturally and specifically heavier than VVater but a piece of Metal of the same specifick weight with Water or VVater it self cannot gravitat in VVater or weigh down the Scale of a Ballance and the reason is because the surface of Water upon which they rest bears them up with as great weight and force as they press down with If it be said that the Water K M rests upon the bottom of the Glass within and therefore if the man above find the weight of the Glass he must find the weight of the Water within it I answer the consequence is bad because the weight of the Water within is sustained and counterpoised by the weight of the Water without whereupon the bottom of the Glass rests That 's to say as there is a Pillar of Water K M within the Glass that presseth down the bottom so there is a Pillar of Water without the Glass whereupon the bottom of the Glass rests and which bears up both But the greater difficulty is this the further down the Glass goes it grows the heavier because of more and more Water that creeps in at G. Now 't is certain the weight Q grows not heavier therefore it must be the Water within the Glass that makes the increase of the weight and therefore Water must still weigh in VVater If this argument had any strength in it it would prove the weight of the VVater I H to gravitat and weigh likewise because the further down this glass goes it grows the heavier because of more and more Water that creeps up from H to I. Now 't is certain the weight of Lead B grows not heavier Behold the difficulty is the same in both and yet it were rashness to affirm the Water I H to be found by a mans hand when he pulls up the Glass with a string seing it is sustained by its own surface and not by any part of the Glass Though this might suffice for an answer yet because the contrary is mantained by some and that with a new Experiment to prove it I shall be at some more pains to vindicat the truth of what I have said This new Experiment to prove that Water weighs in Water I found in a Philosophical Transaction of August 16. Anno 1669. Numb 50 the Invention whereof is attributed by the publisher to that honorable and worthy Person Mr. Boyl whose conclusions and trials I never much called in question but finding this opposite and contrary to what I have demonstrated I shall crave liberty to say amicus Socrates amicus Plato sed magis amica veritas and shall therefore examine it as briefly as may be The words of the Publisher are as follows The Author of this Invention is the Noble Robert Boyl who was pleased to comply with our desires of communicating it in English to the curious in England as by inserting the same in the Latine Translation of his Hydrostatical Paradoxes he hath gratified the Ingenious abroad And it will doubtless be the more welcome for as much as no body we know of hath so much as attempted to determine how much Water may weigh in Water and possibly if such a Problem had been proposed it would have been judged impracticable The Method or Expedient he made use of to perform it as near as he could may easily be learned by the ensuing accompt of a Trial or two he made for that purpose which among his Notes he caused to be registred in the following words A Glass-bubble of about the bigness of a Pullets egg was purposely blown at the flame of a Lamp with a somewhat long stem turned up at the end that it might the more conveniently be broken off This Bubble being well heated to rarify the Air and thereby drive out a good part of it was nimbly sealed at the end and by the help of the Figure of the stem was by a convenient Weight of Lead depressed under Water the Lead and Glass being tyed by a string to a Scale of a good Ballance in whose other there was put so much weight as sufficed to counterpoise the Bubble as it hung freely in the midst of the Water Then with a long Iron Forceps I carefully broke off the seal'd end of the Bubble under Water so as no Bubble of Air appear'd to emerge or escape through the Water but the Liquor by the weight of the Atmosphere sprung into the un-replenish'd part of the Glass-Bubble and fill'd the whole cavity about half full and presently as I foretold the Bubble subsided and made the Scale 't was fastned to preponderate so much that there needed 4 drachms and 38 grains to reduce the Ballance to an equilibrium Then taking out the Bubble with the Water in it we did by the help of a flame of a Candle warily applyed drive out the Water which otherwise is not easily excluded at a very narrow stem into a Glass counterpoised before and we found it as we expected to weigh about four drachms and 30 grains besides some little that remained in the Egg and some small matter that might have been rarified into vapors which added to the piece of Glass that was broken off under Water and lost there might very well amount to 7 or 8 grains By which it appears not only that Water hath some weight in Water but that it weighs very near or altogether as much in Water as the self same portion of Liquor would weigh in the Air. The same day we repeated the Experiment with another sealed Bubble larger then the former being as big as a great Hens-egg and having bâ—oken this under Water it grew heavier by 7. drachms and 34 grains and having taken out the Bubble and driven out the Water into a counter pois'd Glass we found the transvasated Liquor to amount to the same weight abating 6 or 7 grains which it might well have lost upon such accompts as have been newly mentioned Thus he Figure 24. THe design then of this Experiment is to prove that water weighs in Water but it seems there is here a very great mistake which I shall make out after this manner For which cause let this Schematism 24 represent the Experiment already described The â—lass-bubble then is E P F R. The stem is H C the weight that sinks the Glass is B. The surface of Water under which it is drowned is A D. The Ballance to which the Glass is knit by a string is N O. And lastly E F R is the Water that came in and filled the half of the Bubble Now I say it is not the weight of the Water E F R that turnes the Scales above and makes an alteration in the Ballance but ' its only the weight of the Lead B that does it For evincing this consider that all heavy bodies are either lighter in specie than Water
as corkâ— or of the same specifick weight with it as some Wood is or lastâ—y heavier in specie than Water as Lead or Gold Now 't is certain that bodies of the first sort cannot weigh in Water and the reason is because they being naturally lighter their whole weight is supported by the Water and therefore not one part of them can be born up by a Ballance above A piece of Cork that weighs 12 ounces in the Air weighs nothing in Water because as soon as it toucheth the surface the whole weight of it is supported and therefore cannot affect the Ballance above But bodies of the third sort as is clear from experience and reason does really weigh in Water And the reason is because they being naturally heavier than water their whole weight cannot be supported by it and therefore some part of them must burden the Ballance to which the body is knit A piece of Lead that weighs 12 ounces in the Air will not lose above 2 ounces when ' its weighed in Water or may be less But here there is no difficulty The question then is in order to bodies of the same specifick weight with Water as some Wood is or as Water is I say of such also that they cannot weigh in Water and the reason is because they being â—ust of the same weight must have their whole weight supported by it even as one foot of Water supports the whole weight of the foot above it It may be evidenced after this manner Take a piece of Wood that 's lighter in specie than Water and add weight to it by degrees till it become of the same weight with Water Knit it with a string to a Ballance ond weigh it in Water and you will find the whole weight supported by the Water And the reason is because being left to it self it can go no further down than till the upper part of it be level with the surface of the Water Now the whole weight being thus supported not one ounce of it can burden the Ballance In a word the Ballance can never be burdened unless the body that 's knit to it have an inclination to go to the ground when left to it self which a body of the same weight with Water can never have I conclude then if a body of the same weight with Water cannot weigh in Water neither can Water weigh in Water seing Water is of the same weight with Water And Therefore the Water E F R that 's now within the Bubble cannot in anywise burden the Ballance above but must be supported wholly by the Water I K G H upon which the bottom of the Glass rests If it be said that the Glass it self is supported by the Ballance because ' it s heavier in specie than Water therefore the VVater within that rests upon the sides of it must be supported likewise by it I answer the whole weight of the Glass is not supported by the Ballance but only a part the VVater I K G H supporting the other part And this part is just as much as is the weight of VVater that 's expelled by the Glass Now if the said VVater support so much of the Glass because it is the just weight of so much VVater why should it not also support the VVater within the Glass Seing the VVater within the Glass is just the weight of as much VVater as will fill the space E F R. I come in the next place to shew that it is the weight of the Lead B that turns the Scales when the VVater comes in at C and fills the half of the sphere For understanding this let us suppose first the weight that 's in the Scale O to weigh six ounces Secondly that the Glass takes 12 ounces to sink it compleatly under the surface A D. Thirdly the weight B to be 18 ounces namely for this cause first that 12 of it may sink the Glass next that the other six may counterpoise the six in the Scale O. Lastly that the VVater within the Glass weighs six ounces I abstract from the weight of the Glass it self which is not considerable seing the most part of it is supported by the VVater and not by the Ballance Now I say 't is six ounces of the weight B that makes this alteration and turnes the Scales For if 12 ounces sink the Glass below the VVater when ' its full of Air and no Water in it then surely â—ix are sufficient to sink it when it is half full And the reason is because there is a less Potentia or force in six inches of Air by the one half to counterpoise a weight of 12 ounces than in 12 inches of Air. Therefore this Air being reduced from 12 inches to six it must take only six ounces to sink it If this be then the other six ounces that now wants a party to counterpoise them must burden the Ballance and be supported by the Scale and therefore to make a new equipondium again you must make the weight O 12 ounces by adding six to it that it may counterpoise 12 of B the other six being counterpoised by the Air E P F. Let us suppose next this Glass to be compleatly full of VVater and the whole Air expelled In this case the Scale O must have 18 ounces in it for making a new equipâ—ndium The reason is because there being no Air in the Glass to counterpoise any part of B the whole weight of it must be sustained by the Ballance and therefore in the Scale O there must be 18. Now I enquire whether these 18 ounces are the equipondium of the VVater within the Glass or of the weight of Lead B 'T is impossible it can counterpoise them both seing the VVater is now 12 and B 18. It must then either be the counterballance of the Water or the counterballance of the Lead It cannot be the first because 12 cannot be in equipondio with 18 It must then be the second Or if these 18 ounces in the Scale O be the counterpoise of the Water within the Glass I enquire what sustains the weight of the Lead B The weight of it cannot be sustained by the Water because 't is a body naturally heavier than Water it must therefore be sustained by the Ballance I conclude then that Water cannot weigh in Water If it be objected that this conclusion seems to contradict and oppose the Pressure of the Water that 's been hitherto confirmed with so many Experiments I answer the Pressure of the Water is one thing and Water to weigh in Water is another The first is when one Pillar of Water counterpoises another or when a Pillar of Water counterpoises a Pillar of Mercury or is counterpoised by a Pillar of Air all which is in order to the Natural Ballance wherein bodies weigh only according to altitude The second is when VVater is not counterpoised by VVater or by Mercury or by Air or by any other Fluid but when ' its
Pressure that 's in the VVater not only 10 but 20 or 30 fathom without all hazard And the reason is because what Pressure soever is without to press in the sides the same degree of Pressure is within to press them out By this means there is not one part of the VVater how deep soever to which the Ark may come down but there will be found as much force in the Air within as will counterballance the whole weight without as will be infallibly demonstrated afterwards This answers a fourth objection namely if holes be cut out in the sides of the Ark in stead of windows the force of the VVater will break the Glasses in pieces that covers them There is here no hazard though the said windows were 12 inches in Diameter but it s not needful they be so large It 's sufficient if they be 2 inches wide for a mans eye near to a hole 2 inches wide will see a great way about him There 's a necessity the Glasses be joyned in with cement that Water may not have access to come in or Air to go out In such a case ther 's no hazard that the Pressure of the VVater will break through the windows or break the Glasses because the Pressure of the Air within being of the same force with the strength of the VVater without the Glasses are keeped intire It may be enquired what hazard would follow upon supposition a small hole were pierced in the head of the Ark above when it is going down I answer ther 's not so much hazard as a man would think provided the hole be not wide but narrow If it be wide not only the VVater comes in but the Air goes out the one thrusting it self by the other If the hole be no wider than the point of a bodkin is in thickness ther 's no danger at all for by reason of the strait passage the one cannot thrust it self by the other and therefore neither the VVater can come in nor the Air go out And this comes to pass by reason that the Air within is as strong as the Water is without Now if they be both of the same strength and force why ought the Air rather to go out then the Water to come in or the Water rather to come in then the Air to go out I am confident though the hole were as wide as a man might thrust in his little finger yet no irruption of Water or eruption of Air would follow This demonstrats clearly that though a small rift or leak should happen in the Ark yet no hazard or danger would follow thereupon If it be inquired whither the greatest hazard is from the ingress of the Water or from the egress of the Air I answer ther 's no danger from the coming in of the Water from above because as it comes in it falls down and so mingles with the rest below But if the Air should go out the Ark fills presently full of Water and drowns the man that is in it The next thing considerable in this Diving Instrument is the foot-stool of Lead C D that 's not only useful for a man to set his feet upon when he dives but especially for sinking of the Ark. For this being made of Timber and full of Air cannot of ' its own accord go down unless it be pulled and forced by some weight It may either be broad and round or square if square a large foot over from side to side or 16 inches will determine the breadth By this means it will happen to be pretty thick seing a great quantity of Lead is required In each corner there must be a hole for four chords by which it is appended to the mouth of the Ark. Between it and the roof within must be the height of a man and more The weight of it cannot be well determined without trial seing it depends upon the dimensions of the Ark. First then try how much weight will bring the top E F G H level with the surface of the Water When this is found add a little more weight till it begin to sink and this will surely take it to the ground though it were 40 fathom 'T is to be observed that when the top E F is level with the surface there is here a just counterpoise namely between the Lead foot-stool on the one part as a pondus and the Ark on the other part as a potentia for with what force the Ark endeavours to pull up the Lead with the same force strives the Lead to pull down the Ark. Hence it is that as a small weight will turn a pair of Scales when they are in equilibrio so a small weight added to the foot-stool will sink the Ark. Though it may seem difficult to determine the just weight of the foot-stool without trial as I said yet I purpose to essay it For this cause consider that there is no Vessel of VVood almost if it be once full of Water but the orifice of it will ly level with the surface of the VVater wherein it sweems This proposition is so evident from experience that it needs no confirmation From this I gather that as much weight of Lead or Stone will bring the top of the Ark E F G H level with the surface of the VVater as is the weight of the Water that fills it If you suppose then the Ark to be 36 inches broad and 40 inches high it must contain 30 cubique foot of Water Now supposing each square foot of this Water to weigh 56 pound 30 foot must weigh 1680 pound This is gathered from trial and experience for after exact search I found a cubique foot of Water in bulk about 16 pints of our measure to weigh 56 pound Take then a piece of Lead of that weight and you will find it make a just counterpoise with the Ark. If any be desirous to know the quantity of it I answer if lead be 13 times naturally heavier then Water you will find that a piece of Lead about 16 inches every way will do it If it be objected that when a mans body is within the Ark the weight of the foot-stool must be less even as much less as is the weight of the man whom I suppose to weigh 224 pound or 14 stone I answer the whole weight of the man is not to be deduced from the foot-stool but the one half only and the reason is because a mans body being of the same specifick and natural weight with Water it cannot preponderat or weigh in VVater because magnitudes only naturally heavier then VVater weigh in VVater as Lead or Stone therefore seing the one half of the man is within the Ark and the other without among the Water that part only must weigh that 's invironed with Air. This may seem a plausible answer and might do much to satisfy these that are not very inquisitive yet being examined it will be found unsufficient Therefore I say there 's
a magnitude of Water 34 foot in hight 12 inches in length and six inches in breadth Though the weight of any Pillar of Air may be known by knowing only the dimensions of it in breadth and length yet the weight of a Pillar of Water cannot be known unless all the three common dimensions of it be first known The reason is this the Pillars of Air are all of the same hight but the Pillars of Water in the Ocean are of different hights therefore not only must they be known secundum longitudinem latitudinem in length and breadth but secundum profunditatem that is according to deepness 'T is easie to know then what each particular Pillar weighs First then try how much weight is in a cubical foot of Water and having found this to be v. g. 56 pound you may determine that a Pillar of Water 34 foot high and 12 inches thick weighs 1904 pound A Pillar 34 foot high and six inches thick weighs 476 pound Note that in a Cube of Water six inches thick there are 216 inches which weighs seven pound In a Pillar 12 inches thick and 20 fathom or 100 foot high you will find 5600 pound weight In one of the same thickness but 200 fathom high there are 56000 fifty six thousand pound weight In a Pillar three foot square and 20 fathom deep there are 50400 fifty thousand and four hundred pound weight Make it 800 fathom high with that thickness and it will weigh 504000 five hundred and four thousand pound But if according to the Theorem 25 you consider the weight of the Air above it will weigh 521136 five hundred twenty and one thousand one hundred thirty and six pound A Pillar 12 foot square and 300 fathom deep weighs 12096000 twelve million ninety and six thousand pound Lastly suppose there were a bulk of Water 500 fathom deep and 500 fathom thick such a magnitude would weigh 8750000000 eight thousand seven hundred and fifty million of pounds But if the Pressure of the Air that rests upon a surface of Water 500 fathom in breadth and length be taken in that weighs 119000000 a hundred and nineteen million of pounds the total that the bottom of the sea sustains must be 8940000000 eight thousand nine hundred and fourty million of pounds or 558750000 five hundred fifty and eight million seven hundred and fifty thousand stone weight I infer from the fifth assertion that the lightest of Fluids may be brought to an equilibrium with the heaviest For though Mercury be 14000 times heavier than Air yet the part of the surface A is no more prest with the Mercury A B then the part C is prest with the Air C D. Secondly that 29 inches of Mercury are of the same weight with 34 foot of Water Thirdly the heavier a Fluid be naturally it hath the less altitude in the Natural Ballance and contrariwise the lighter it be it hath the more altitude This is clear from the Mercury that 's 29 inches the Water that 's 34 foot and the Air that 's counted 6867 fathom I infer from the sixth assertion that two Fluids of different gravities may make an equilibrium with a third of the same kind Because the 27 foot of Air I G and the 17 foot of Water E K are in equilibrio with the Air F H. I infer secondly that 17 foot of Air may be as heavy as 17 foot of Water because the Air I G is exactly as heavy as the Water E K. I infer thirdly that the Bensil of a Fluid is a thing really distinct from the Natural weight of it because the Pressure of the Air I G is 952 pound but the natural weight of it will not exceed if it were weighed in a Ballance two or three ounces I infer fourthly that Air cannot suffer dilatation but it must lose of it's Pressure Because the Air I G that ought to weigh 1904 pound weighs only 952. For understanding this you must know that when a Pipe is about half full of Air and half full of Water and inverted so much of the Water falls out and consequently so many inches doth the Air above it expand it self So to make this Pipe that 's 34 foot high half full of Air and half full of Water you must pour in about 19 foot of Water and the 15 foot of Air that 's in it besides will when the Pipe is inverted go up and expand it self to 17 foot two foot of Water falling out I infer from the seventh assertion that when there are two Fluids of different gravities and weights counterpoising a third by what proportion the one grows lighter by that same proportion the other becomes heavier For when the VVater E K that weighs 952 pound becomes E N that weighs 476 the Air above it that weighed 952 becomes now 1428 pound I infer from the eighth that the pondus of a Fluid cannot be counterpoised by two distinct powers Because the 34 foot of Water E G cannot be both sustained by the part of the surface of Air E and my hand I infer from the ninth that the Pressure and weight of a Fluid may be found even in its own Element by sense Because in poising of the Tub I find the weight of the Air L M. I infer secondly that the weight of a Fluid is only found in its own Element when there is not a potentia to counterpoise the pondus of it because I find only the weight of the Air L M because it wants a potentia to counterpoise it I infer thirdly that it is very possible even in the Artificial Ballance to weigh a Fluid in its own Element and to know the precise weight of it to a grain For this cause take a small chord and fasten therewith the top of the Pipe G to the Scale of a Ballance and the Lead or Stone that makes the counterpoise in the opposite Scale is the just weight of the Air L M. To put a close to this Experiment let us suppose the Pipe E G to be 68 foot high and void of Air. If then the orifice E be drowned among stagnant Water the Liquor of its own accord as it were will rise from E to K 34 foot the other half I G remaining empty This evidently shews that the Pressure of the Air hath a Sphere of Activity beyond which it is not able to raise or press up a pillar of VVater 'T is folly then to think that Water may be conveyed over high places by the help of a Siphon v. g. from the one side of a Hill over the top to the other side For if that hight exceed perpendicularly 34 foot no Art will do it Yet contrariwise it is possible to transport Water by Pipes and Siphons not only 34 foot below the source but 3400. Nay if there were a Siphon passing from the surface of the Earth to the Center and thence rising to the surface again it would convey Water from the one place to the
also for if a Cube of Timber resting in the space T be just the weight of the Water T the imaginary surface O T V is no more prest then if T were Water and so it cannot go downward neither can it go upward seing the under part of the Water R is no more prest up by the Timber T then if the space T were filled with Water If it be said according to this reasoning a Stone may be suspended in a deep Water between the top and the bottom which is absurd I answer such a thing may happen in a very deep Water For put the case a Cube of Lead twelve inches every way were to go down twelve thousand fathom it is probable it would be suspended before it came to the ground For coming to an imaginary surface far down where the Pressure is great a Cube of Water twelve inches thick there may be as heavy even specifically as the Cube of Lead is though the Lead be ten times heavier specifically then any foot of VVater at the top If Water suffer compression of parts by the superiour burden it is more then probable that the second foot of Water burdened with the first hath moe parts in it then are in the first and the third moe then in the second and so forth and consequently that the second is heavier then the first and the third heavier then the second Now if this be why may not that foot of Water that hath sixty thousand foot above it by vertue of this burden be so comprest that in it may be as many parts as may counter-ballance a Cube of Lead twelve inches every way If then that imaginary surface that is sixty thousand foot deep be able to sustain the said foot of VVater which perhaps weighs twenty pound why may it not likewise sustain the Lead that is both of the same dimensions with it and weight Hence it is that the Clouds do swim in the Air by vertue of a counter-ballance And we see which confirms this Doctrine that the thinnest and lightest are alwayes farthest up and the thickest and blackest are alwayes farthest down THEOREM XVII The lower the parts of a Fluid are they are the heavier though all of them be of equal quantity and dimensions Figure 1. THis follows from the former which may appear a Paradox yet it seems to be true for though the Water Q at the bottom be of the same dimensions with the Water E at the top yet it is really heavier which happens as I said from the superiour Pressure It is clear also from this namely the Cube of Timber E which swims upon the surface being thrust down to Q comes up to the top again which could not be unless the Water Q were heavier then the Water E. I suppose the Water E and the Timber E to be exactly of the same specifick weight and consequently the surface of the Timber to ly Horizontal with B C D. Now the reason why the Timber ascends from Q to E is no other then this namely that the one Water is heavier then the other for the under part of the Water P being more prest up with the Timber existing in Q then with the Water Q it self it must yeeld and give way to the ascent for if the Cube of Timber existing in Q were as heavy as the Water Q it self it would no more press upon P or endeavour to be up then the Water Q does THEOREM XVIII A heavy body weighs less in Water then in Air. Figure 1. THis is easily proven from experience for after you have weighed a stone in the Air and finds it two pound and an half take it and suspend it by a threed knit to the scale of a ballance and let it down into the Water and you shall find it half a pound lighter The question then is why doth it lose half a pound of its weight I answer the stone becomes half a pound lighter because the surface of Water on which it rests sustains half a pound of it For put the case a stone were resting in R that weighed two pound and an half in the Air it behoved to weigh but two pound in this Water because the Water T sustains half a pound of it For if this Water T be able to sustain the Water R that weighs half a pound it must be also able to sustain half a pound of the stone seing half a pound of stone is no heavier then half a pound of Water Note that when a heavy body is weighed in Water it becomes so much lighter exactly as is the weight of the Water it thrusts out of its own place THEOREM XIX A heavy body weighs less nigh the bottom of the Water then nigh the top thereof Figure 1. FOr clearing this proposition I must suppose from the 17. Theorem that the lower the parts of Water be they are the heavier though all of them be of equal dimensions If then the lowest foot Q be heavier that is have moe parts in it then the foot N it of necessity follows that a stone suspended in Q must be lighter then while it is suspended in N or I. Because if a stone be lighter in Water then in Air as is said even by as much as is the weight of the bulk of Water that the bulk of the stone expells then surely it must be lighter in the one then in the other place because suspended in Q it expells moe parts of Water then while it is suspended in N or I. For example let us suppose the Water N to weigh eight ounces and the Water Q to weigh nine then must the stone suspended in Q weigh less by an ounce then suspended in N seeing as much is deduced from the weight of the stone as is the weight of the Water it expells but so it is that it thrusts nine ounces of Water out of its own place in Q and but eight in N or I therefore it must be one ounce lighter in the one place then in the other This may be tried with a nice and accurat ballance which will bring us to the knowledge of this namely how much the foot of Water Q is heavier then the Water N or O. THEOREM XX. One part of a Fluid cannot be under compression unless all the parts next adjacent be under the same degree of Pressure Figure 1. THis proposition may be proven by many instances for when the Air of a Wind-gun is reduced to less quantity by the Rammer all the parts are most exactly of the same Bensil So is it in a Bladder full of wind It 's true not only in order to this artificial Pressure but in order to the natural Pressure and Bensil of the Air likewise For the Air within a parlour hath all its parts under the same degree of natural compression so is it with the parts of the Air that are without and immediatly under the weight of the Atmosphere It s evident also in
the parts of Water for the foot of Water R cannot be under Pressure unless the Water S and N be under the same degree of it Though this be true of Fluids while all the parts lye in the same Horizontal surface yet to speak strictly it will not hold true of the parts scituated under divers surfaces for without question the foot of VVater T must be under four degrees of Pressure if the VVater R be under three And if the Air in the lowest story of a building be under six degrees of Bensil the Air in the highest story must be under five If a man would distinguish Metaphysically and subtilly he will find a difference of this kind not only between the first and second fathom of Air nearest to the Earth but between the first and second foot yea between the first and second inch and less much more in Water as to sense However it be yet the Theorem holds true for we find no difference sensible between the compression of Air in this room and the compression of Air in the next room above it no not with the Baroscope or Torricellian Experiment that discerns such differences accurately I judge it likewise to be true in order to the next adjacent parts of Fluids of different kinds for while a surface of Mercury is burdened with a Pillar of Water or a surface of Water with a Pillar of Air whatever degree of weight and Pressure is in the lowest parts of these Pillars the same is communicated entirely to the surfaces that sustains them So then there is as much force and power in the surface of any Water as there is Weight and Pressure in the lowest foot of any Pillar of Air that rests upon it otherwise the surface of Water would never be able to support the said Pillar for a surface of six degrees of force can never be able to sustain a a Pillar of Air of eight or ten degrees of weight THEOREM XXI The Pressure of Fluids may be as much in the least part as in the whole Figure 1. THis Theorem may seem hard yet it can be made manifest by many instances for albeit the quantity of Air that fills a Parlour be little in respect of the whole Element yet surely there is as much Pressure in it as in the whole because Experience shews that the Mercurial Cylinder in the Baroscope will be as well sustained in a Chamber as without and under the whole Atmosphere directly which could not be unless the small portion of Air that 's in this Parlour had as much Pressure in it as in the whole Element Besides this it will be found in a far less quantity for though the Baroscope were inclosed and imprisoned so closs within a small Vessel that the Air within could have no communion with the Air without yet the Pressure of that very small quantity will sustain 29. inches of Mercury and this will come to pass even though the whole Element of Air were annihilated This Proposition is likewise evident in order to the Pressure of the Water for put the case the Baroscope whose Mercurial Cylinder is 29. inches by the Pressure of the Air were sent down to the bottom of a Sea 34. foot deep within a Vessel as a Hogs-head and there exactly inclosed that the VVater within could have no commerce with the VVater without yet as well after this shutting up as before other 29. inches would be sustained by the Pressure of this imprisoned VVater which proves evidently that there is as much Pressure in one Hogs-head full of VVater at the bottom of the Sea as in the whole Element of VVater above or about for an Element of VVater never so spacious if it exceed not 34. foot in deepness can sustain no more Mercury then 29. inches by its Pressure Yea though the Vessel with the Baroscope and imprisoned VVater in it were brought above to the free Air yet will the VVater retain the same Pressure and will de facto sustain 29. inches of Mercury provided the Vessel be kept closs It is therefore evident that as much Pressure may be in one small quantity of VVater as in the whole Element or Ocean 'T is to be observed that this Theorem is to be understood chiefly of the lower parts of Fluids seing there cannot be so much Pressure in the VVater P as in the VVater Q for in effect there is as much Pressure in the VVater Q as is in the whole VVater above it or about it From this Theorem we see evidently that the Pressure and Bensil of a Fluid is not to be measured according to its bulk and quantity seing there is as much Bensil in one foot nay in one inch of Air as is in the whole Element and as strong a Pressure in one foot of VVater or less as there is in the whole Ocean therefore the greatest quantity of Air hath not alwayes the greatest Bensil neither the greatest quantity of VVater the greatest Pressure But this will appear more evident afterwards THEOREM XXII The Pressure and Bensil of a Fluid is a thing really distinct from the natural weight of a Fluid Figure 1. THis may be easily conceived for as in solid bodies the Bensil and natural weight are two distinct things so is it in Air and Water or in any other Fluid The weight of a Bow is one thing and the natural weight of it is another The weight of the Spring of a Watch and the Bensil of it are two distinct things The weight perhaps will not exceed two ounces but the Bensil may be will be equivalent to two pound Though these may illustrate yet they do not convince therefore I shall adduce a reason and it 's this The natural weight of a Fluid is less or more as the quantity is less or more but it is not so with the Pressure because there may be as much Pressure in a small quantity as in a great as is evident from the last Theorem therefore they may be different The first part of the Argument is manifest because there is more weight in a gallon of Water then in a pint A second reason is because a Fluid may lose of its pressure without losing of its weight This is evident from the Schematism for if you take away the four foot of Water E F G H and consequently make the four Pillars shorter the foot of Water Q becomes of less Pressure but not of less Weight seeing the quantity still remains the same at least the loss of weight is not comparable to the loss of Pressure I say it becomes of less Pressure because there is a less burden above it Thirdly the Pressure and Bensil may be intended and made stronger without any alteration in the weight so is the Bensil of Air within a Bladder made stronger by heat without any alteration in the weight of it Likewise the Pressure of the foot of Water Q may be made stronger by making these four
degree of Pressure with the VVater E or L without or with the VVater K or F. And which is strange let us suppose both the entries E and F stopped and nothing remaining open but the hole G which I judge no wider then may admit the hair of ones head yet thorow that smal hole shall the Pressure be communicated to the parts of the Water within in as high a degree as if the upper part of the Vessel E M L were cut off to let the Pressure come down directly What is true in order to Water the same is true in order to Air or Mercury or any other Fluid For though a house were built never so closs without door or window yet if there remain but one smal hole in it the Pressure of the whole Atmosphere shall be transmitted thorow that entrie and shall reduce the Air within the house to as high a degree of Bensil as the Air without THEOREM XXXI The Pressure and Bensil of a Fluid that 's in the Lowest foot is equivalent to the weight of the whole Pillar above Figure 5. FOr understanding this Proposition let us suppose E F to be the lowest foot of a Pillar of Air cut off from the rest and inclosed in the Vessel E F six inches in Diameter or wideness and twelve inches high Now I say the Bensil and Pressure that 's in that one foot of Air is exactly of as great force and power as is the weight of the whole Pillar of Air from which it was cut off Let A B be that Pillar of Air which I suppose is six inches thick and six thousand fathom high Take it and weigh it in a Ballance and say it weighs 500 pound yet the Pressure and Bensil that 's in the Air E F is of as much force and if the one be of strength by its weight to move v. g. a great Clock the other by its Bensil will be of as much This proposition is true also in order to Water For put the case E F were the lowest of 34 foot of Water in it will be found as much Pressure and force as will be equivalent to the weight of the whole thirty three foot from which it was cut off But here occurreth a difficulty for if the Pressure and Bensil of the foot of Air E F be equivalent to the weight of the whole Pillar of Air A B which weighs 500 pound then must the slender Pillar of Air C D that 's but two inches in diameter be as heavy weighed in a ballance as the thicker Pillar A B which is absurd I prove the connexion of the two parts of the Argument thus as the Bensil of the Air G H is to the Bensil of the Air E F so is the weight of the Pillar C D to the weight of the Pillar A B but so it is that the Bensil of the Air G H is equal in degree to the Bensil of the Air E F according to the Theorem 21. Where it 's said that the Pressure of Fluids may be as much in the least part as in the whole therefore the Pillar C D and the Pillar A B must be of equal weight when both are weighed together in the opposite scales of a Ballance which is false seing the one is far thicker and so heavier then the other There 's no way to answer this objection but by granting the Air G H and E F to be equal in Bensil and yet the two Pillars unequal in weight because according to the 22 Theorem the Bensil of a Fluid is one thing and the natural weight is another THEOREM XXXII In all Fluids there is a Pondus and a Potentia a weight and a power counterpoising one another as in the Staticks THat part of the Mathematicks which is called Staticks is nothing else but the Art of weighing heavy Bodies in which two things are commonly distinguished viz. the pondus and the potentia the weight and the power 'T is evident while two things are counterpoising one another in the opposite scales of a Ballance as Lead and Gold the one being the pondus the other the potentia The same two are as truly found in the Hydrostaticks for while the Mercurial Cylinder is suspended in the Torricellian Experiment by the weight of the Air the one is really the pondus the other the potentia Or while into a Siphon with the two orifices upward Water is poured there arises a counterpoise the Water of the one Leg counter-ballancing the Water of the other this taking the name of a pondus the other the name of a potentia 'T is evident also while a surface of Water sustains a Pillar of Water this being the pondus that the potentia Or while a surface of Water sustains a Pillar of Air the Pillar of Air being the pondus and the surface of Water the potentia Or while a surface of Quick-silver sustains a Pillar of Water or Air the surface is the power and either of the two is the pondus or weight as you please THEOREM XXXIII Fluid Bodies can never cease from motion so long as the pondus exceeds the potentia or the potentia the pondus THis is a sure Principle in the Hydrostaticks which will appear most evident while we pass thorow the subsequent Experiments I shall only now make it appear by one instance though afterwards by a hundred In the Torricellian Experiment lately mentioned 't is observed that though the Pipe were never so long that 's filled with Mercury yet the Liquor subsides and falls down alwayes till it come twenty nine inches above the surface of the stagnant Mercury below The reason whereof is truly this so long as the Mercury is higher then the said point as long doth the pondus of it exceed the potentia of the Air therefore the motion of it downward can never cease till at last by falling down and becoming shorter it becomes lighter in which instant of time the motion ends both of them being now in equipondia or in evenness of weight THEOREM XXXIV When two Fluids of different kinds are in aequilibrio together the height of the one Cylinder is in proportion to the height of the other 〈◊〉 the natural weight of the one is to the natural weight of the other FOr understanding this Theorem we must consider that when two Cylinders of the same kind as one of Water with Water or as one of Mercury with Mercury are counterpoising one another both are of the same altitude because both are of the same natural weight But when the two are of different kinds as a Cylinder of Air with Mercury or as a Cylinder of Air with Water or as a Cylinder of Water with Mercury then it will be found that by what proportion the one Liquor is naturally heavier or lighter then the other by that same proportion is the one Cylinder higher or lower then the other For example because Air is reckoned 14000 times lighter then
Quick-silver therefore the Pillar of Air that counterpoiseth the Pillar of Quick-silver in the Torricellian Experiment is 14000 times higher The one is 29 inches and therefore the other is 406000 inches which will amount to 33833 foot or about 6766 fathom counting five foot to a fathom And because Air is counted 1000 times lighter then Water therefore the Pillar of Air that sustains the Pillar of Water is 1000 times higher The hight of Water by the Pressure of the Air is 34 foot and therefore the hight of the Air is a thousand times 34 foot And because Water is reckoned 14 times lighter than Mercury therefore you will find even by experience that the Pillar of Water that counterpoises the Pillar of Mercury is 14 times higher For if the Mercury be ten inches the Water will be exactly 140. If it be 29 inches the Water will be thirty four foot The reason is evident because if one inch of Mercury be as heavy naturally as 14 inches of Water it follows of necessity that for making of a counterpoise to every inch of Mercury there must be 14 of Water and these in altitude each one above another Hydrostatical EXPERIMENTS For demonstrating the wonderful Weight Force and Pressure of the Water in its own Element EXPERIMENT I. Figure 6. IN explicating the Phenomena of the Hydrostaticks and in collecting speculative or practical conclusions from them I purpose to make choise of the plainest and most easie Experiments especially in the entry that this knowledge that 's not very common and yet very useful may be communicated to the meanest capacities For if at the first any mystical or abstruse Experiments should be proposed with intricate descriptions they would soon discourage and at last hinder the ingenuous Reader from making progress For if a man do not take up distinctly the Experiment it self first he shall never be able to comprehend next the Phenomena nor at last see the inferences of the conclusions Next though some of the trials may seem obvious yet they afford excellent Phenomena by which many profound secrets of Nature are discovered And if that be 't is no matter what kind they be of Then the grand design here is not to multiply bare and naked Experiments for that 's a work to no purpose for it 's like a foundation without a superstructure but the intention is not only to describe such and such things but to build such and such Theorems upon them and to infer such and such conclusions as shall make a stately building and give a man in a short time a full view of this excellent Doctrine For the first Experiment then prepare a Vessel of any quantity as A B C D near half full of Water whose surface is M H. Prepare also two Glass-pipes the one wider the other narrower open at both ends which must be thrust down below the Water first stopping the two upper orifices E and F. This done open the said orifices and you shall see the Water ascend in the wider to G and in the narrower to H. Now the question is What 's the reason why the Water did not ascend the orifices E and F being stopped and why it ascends they being opened To the first part I answer the Water cannot ascend because the imaginary surface of Water L K is equally and uniformly prest for with what weight the outward Water M L and H K press the said surface with the same weight doth the Air within the two Pipes press it To the second part I answer the Water ascends because the same surface the orifices E and F being opened is unequally prest for the outward Water M L and H K press it more then the Air within the Pipes do The difficulty only is why it is equally prest the orifices E and F being stopped and why it is unequally prest the said orifices being once opened To unloose the knot I must shew the reason why the Air within the Pipes press the surface L K with as great a burden as the outward Water press it For understanding this you must know that when the orifice I is thrust down below the Water there ariseth a sort of debate between the lower parts of the Water and the Air within the Pipes the Water striving to be in at I and the Air striving to keep it out but because the Water is the stronger party it enters the orifice I and causeth the Air retire a little up one fourth part or sixth part of an inch above I and no more which is a real compression it suffers For the orifice E being stopped hinders any more compression than what is said in which instant of time the debate ends the Air no more yeelding and the Water no more urging by which means the Air having obtained a degree of Bensil more then ordinary by the Pressure of that little quantity of Water that comes in at I presseth the part of the imaginary surface it rests upon with as great weight as the outward Water presseth the parts it rests upon But when the orifice E is opened the outward water M L and H K press the imaginary surface L K more than the Air within the Pipe can do And the reason is because by opening the orifice above the internal Air that suffered a degree of Bensil more then ordinary presently is freed and consequently becomes of less force and weight which the Water finding that hath a little entered the orifice I instantly ascends to G it being less pressed then the Water without the Pipe Now the reason why it ascends no higher then G is taken from the equal Pressure of the Body that rests upon the surface M G H For assoon as it comes that length all the parts of the horizontal Plain of Water is uniformly prest with the incumbing Air both within the Pipe and without the Pipe The Water in going up cannot halt mid-way between I and G for then there should be an unequal Pressure in Fluids without motion which is impossible for the Water is still stronger then the Air till once it climb up to G. From this Experiment we see first that in Water there is a Pressure and Force because having opened the orifice E which is only causa per accidens of this motion the Water is prest up from I to G. We see secondly that Fluid Bodies can never cease from motion till there be an equal Pressure among the parts which is evident from the ascent of the Water from I to G which cannot halt in any part between I and G because of an unequal Pressure till it once climb up to G. We see thirdly that Fluid Bodies do not sustain or counterpoise one another according to their thickness and breadth but only according to their altitude because there is not here any proportion between the slender Pillar of Water H K within the Pipe and the outward Water that sustains it I mean as to the thickness therefore 't is no
high But assoon as the Tub is reclined there arises ane inequality between the saids two parties the Pondus of the Cylinder becoming now less than before If you say the quantity of the VVater is the same namely 50 inches in the reclined Tub as well as in the Perpendicular I grant the quantity is the same but the weight is become less Now the reason why the same individual VVater is not so heavy as before is this there are 40 ounces of it supported by the sides of the Tub within which were not while the Tub was erected for in this position the whole weight of the Cylinder rests upon the surface but while the Tub is reclined the said surface is eased and freed of 40 ounces of it this 40 resting and leaning upon the sides of the Pipe within The surface then finding the said Cylinder lighter now than before instantly drives it up from R to E 40 inches And likewise when the reclined Pipe is made Perpendicular the Water falls down from I to D because of the inequality that 's between the Pondus of the Pillar and the Potentia of the surface this surface 50 inches deep not being able to support a Pillar 90 inches high for if this were then one part should be more burthened than another which is impossible It is to be observed that by how much the more the Tub is reclined from a Perpendicular towards the horizontal surface A B C by so much the more growes the inequality between the Pondus and the Potentia and that according to a certaine proportion Hence is it that the Tub being reclined from 60 degrees to 50 there arises a greater inequality between the Pondus of the Cylinder and the Potentia of the surface than while it is reclined from 70 to 60 and more yet in moving from 50 to 40 than in moving from 60 to 50 and so downward till it be horizontal in which position the whole Pondus is lost And contrariwise while the Pipe is elevated the Pondus begins to grow and growes more being lifted up from 10 to 20 than from 1 to 10 and yet more in travelling from 20 to 30 than from 10 to 20 and so upwards till it be Perpendicular in which position the Cylinder regaines the whole Pondus and weight it had This proportion is easily known for it s nothing else but the proportion of Versed Sines upon the line F B for according to what measure these unequal divisions become wider and wider from 90 to 1 according to the same proportion does the Pondus of the Cylinder become less and less and contrariwise according to what proportion the said divisions become more and more narrow from 1 to 90 according to the same measure and rate does the Pondus of the Cylinder become greater and greater EXPERIMENT VI. Figure 9. THis Schematism represents a Vessel fall of Water whose first and visible surface is H I K the second which is imaginary is E F G the third A B C D. Besides these three in Water conceive a fourth in the Air above the Water namely L M N. Upon this aërial surface rests the orifice M of the Tub T M open above Upon the surface E F G is standing the mouth F of the Pipe S F. And upon the surface A B C D stands the Pipe R B open at both ends After the orifice B is drowned below the VVater you will find the Liquor rise from B to H. Then close with the pulp of your Finger the mouth R and lift the Pipe so far up till it have the Position of the Pipe S F and you shall see the VVater hing in it between F and O. Lastly bring the said orifice compleatly above the VVater till it have the position of the Tub T M yet shall the VVater still hing in it as M P. The first question is what sustains the VVater I O for the part F I is sustained by the ambient VVater I answer it cannot be the pulp of the Finger closing the orifice S for though by taking away the Finger the VVater O I falls down and by putting to the Finger it is keeped up yet this proves not the pulp of the Finger to be the principal and immediat cause I say then the VVater O I is suspended by the weight of the incumbing Air resting upon the surface H I K. For understanding this consider as I said before 25. Theorem that the Pressure of the Air upon all Bodies is just equivalent to the weight of 34 foot of VVater Hence then is it that if the Air be able to sustain a Pillar of VVater 34 foot high it must be able to sustain the short Pillar O I that exceeds not four foot The second question is whether the part F be equally burthened with the part E or G for it would seem not seing the VVater O I F is but four foot high whilest upon E or G is resting not only more then a foot of VVater to the top H I K but the whole weight of the Atmosphere upon the said top is resting which is equivalent to the burden of 34 foot of VVater I answer there 's more to be considered than that four foot of VVater which in it self is but of small burden therefore to this we must add the weight of the Air between O and S within the Pipe remember that the orifice S is stopped with the pulp of the Finger which in effect will be as heavy as 31 foot of VVater Put the case then F to be one foot below the first surface H I K and the VVater O I to be three foot then ought the Air O S to have the weight of 31 foot because the surface E F G is able to support a Pillar of 35 foot This I prove because the part E de facto sustains 35 foot because the Air above is equivalent to 34 foot of it and there is a foot of VVater between it and the top namely between E and H. The third question is how it comes to pass that the Water still remains in the Pipe after the orifice M is brought above the surface of the Water for there is here no stagnant Water guarding it as guards the orifice F. I answer that the base M of this Pillar of Water P M as really rests upon the horizontal surface of this Air L M N as a Cylinder of Brass or Timber rests upon a plain Marble Table and after the same manner Remember that the orifice T is stopped all this time with the pulp of the Finger If it be said that the part M is more burdened then the part N seing it sustains four foot of Water which the part N supports not and the Air P T within the Pipe also which is of as much Bensil and Pressure as the Air N Y is of For clearing of this difficulty consider that the Pillar P M is shorter now than before for the orifice M coming up from
D some inches of Water falls out as will be found by experience Suppose then that of four foot six inches fall out if this be then the inclosed Air between P and T must be 〈◊〉 inches longer if this be then of necessity the Bensil of it must be proportionably remitted and slackened whence follows by Metaphysical necessity that it cannot burden the Water P M with as much weight as it had and consequently the surface of Air cannot be so much burdened It must then be no more buâ—dened with them both together than it is with the single Pillar of Air Y N. If then the Water P M be three foot and an half the weight of the enclosed Air T P must be exactly the weight of thirty foot of Water and an half From this experiment we see first the Pressure of the Air for by it the Water O I is suspended and by the same pressure is the Water P M suspended We see secondly that in Air there is a power of dilating it self and that this dilatation never happens without a relaxation of the Bensil We see thirdly that one Fluid cannot sustain another unless the Potentia of the one be equal to the Pondus of the other as is clear from the Aërial surface that cannot sustain the whole four foot of Water but suffers six inches of it to fall out that the Pondus of the rest and the Air above it may become equal to its own Potentia We see fourthly that Fluid Bodies have not only a power of pressing downward but of pressing upward likewise as is clear from the Water O I that 's suspended by the Air pressing down the surface of Water H I K. It presseth upward also while it supports the Water P M. This Experiment also answers a case namely whether or not it is alwayes needful to guard the orifice of the Tub of the Baroscope with stagnant Quick-silver I say then it is not alwayes needful provided the orifice be of a narrow diameter for experience tells that while it is such the Mercury will subside and halt at 29 inches above the orifice though no stagnant Mercury be to guard In making this trial the orifice must be no wider than may admit the point of a needle Or suppose it to have the wideness of a Tobacco-pipe yet will the Mercury be suspended though the end be not drowned among stagnant Quicksilver even as the Water P M is kept up without stagnant Water about it For trial of this you must first let the end of the Pipe be put down among stagnant Mercury and after the Cylinder is fallen down to its own proper altitude lift up the Pipe slowly till the orifice come above the surface and you will find provided you do not shake the Pipe the Cylinder to be suspended after the same manner immediatly by the Air as the Water P M is EXPERIMENT VII Figure 10 11. TAke a Vessel of any quantity such as A B C D E and fill it with VVater And a Glass-pipe such as G F D of 15 or 20 inches long of any wideness closs above and open below Before you drown the open end among the VVater hold the Glass before the fire till it be pretty hot and having put it down you will see the VVater begin to creep up till it come to F where it halts The question now is what 's the reason why the VVater creeps up after this manner 10 or 12 inches above the surface A B I answer the heat having rarified the Air within and by this means having expelled much of it and the Air now contracting it self again with cold the VVater ascends being prest up with the weight of the incumbing Air resting upon the surface of Water A B. There is here surely an inequality between a Pondus and a Potentia that must be the cause of this motion I judge then the inequality to consist between the weight of the Air within the Pipe and the surface of Water C D E. To explicate this I must suppose the Pipe to be thrust down cold in this case little or no Water can enter the orifice D. And the reason is because the Pondus of the Air within the Glass is equal to the Potentia of the surface C D E. But when the Pipe is thrust down hot much of the Air having been expelled by the heat and now beginning to be contracted by cold the Pondus of the Air becomes unequal to the Potentia of the surface and therefore this being the stronger party drives up the Air within the Glass till by this ascent the Pondus of the Air G F and the Pondus of the Water F D together become equal to the Potentia of the surface C D E that sustains them For a second trial bring a hot coal near to the side of the Glass between G and F and you will find the Water to creep down from F toward the surface A B and if it continue any space it will drive down the whole Water and thrust it out at D. To explicate this I must suppose that heat by rarifying the Air within the Glass intends and increaseth the Bensil of it and the Bensil being now made stronger there must arise an inequality between the Pondus of the said Air and the Potentia of the surface C D E the Air then being the stronger party causeth the surface to yeeld By comparing this Experiment with the former we see a great difference between the dilatation of Air of its own accord and by constraint For while it is willingly expanded the Bensil begins to grow slack and remiss and loseth by degrees of its strength even as the Spring of a Watch by the motion of the Wheels becomes remiss But when the dilatation is made by heat and the Air compelled to expand and open it self the Bensil becomes the stronger and the Pressure the greater Notwithstanding though the Bensil of this inclosed Air G F may be made stronger by heat to the expulsion of the Water F D yet if this rarefact on continue any time the Bensil becomes dull and slack And the reason is because Air cannot be expanded and opened to any quantity an inch cannot be dilated and opened to an hundred or to a thousand neither can the Bensil of it be intended and increase to any degree v. g. from one to 20 30 or 100. And therefore as the expansion grows the Bensil must at length slacken But if so be the Air were inclosed as in a bladder knit about the neck with a string then the more heat the more Bensil for in this case there is a growth of Pressure without dilatation And sometimes the Bensil may be so intended with the heat that the sides of the bladder will burst asunder From this Experiment we see first a confirmation of the 21 Theorem namely that there may be as much Bensil and Pressure in the smallest quantity of a Fluid as in the greatest as is
clear from the Bensil of the Air G F which in effect counterpoiseth the weight of the whole Atmosphere resting upon the surface of Water A B. We see secondly that when the pondus and the potentia of two Fluids are in equilibrio or of equal strength a very small addition to either of them will cast the ballance For if a man should but breath softly upon the side of the Glass between G and F or lay his warm hand to it the said Air will presently dilate it self and by becoming thus stronger thrust down the Water and so overcome the potentia of the surface We see thirdly a confirmation of the sixth Theorem namely that the Pressure of Fluids is on every side as is clear from the inclosed Air G F that not only presseth down the Water F D but with as great force presseth up the top of the Glass within and presseth upon all the sides of it within with the same force This Experiment also leads us to the knowledge of two things First of the reason why with cold the Water ascends in the common Weather-glasses and why in hot weather the Water descends Secondly from this Experiment we may learn to know when the Air is under a greater Pressure and when under a lesser because when the Air becomes heavier as in fair weather the Water creeps up in some measure it may be two or three inches when there is no alteration as to heat and cold and in foul weather or in great winds when the Air is really lighter the said Water creeps down as much If it be asked how shall I know whether it be the cold of the Air or heaviness of the Air that causeth the Water to ascend and whether it be the heat of the Air or the lightness of the Air that causeth the Water to descend I have proposed this question of purpose to let you see a mistake Many believe that the ascent and descent of Water in common Weather-glasses is allanerly from the heat and coldness of the Air and therefore they conclude a cold day to be because the Water is far up whereas the Water hath ascended since the last night by reason of a greater weight in the Air which alwayes is when the weather is dry and calm though there hath been no alteration of heat to cold If it be asked how come we to the knowledge of this that the pressure and weight of the Element of Air is sometimes less and sometimes more I answer this secret o Nature was never discovered till the invention of the Torricellian Experiment otherwise called the Baroscope For after the falling down of the Quick-silver to 29 inches if you suffer it to stand thus in your Parlour or Chamber according as the Pressure and weight of the Element of Air becomes more or less so will the Altitude of the Mercury become less or more and vary sometimes above 29 inches and sometimes below This alteration is very sensible which is sometimes the tenth part of an inch sometimes the sixth and sometimes the third according as the weight of the Air is less or more From December to February I found the alteration become less and more from 30 inches to 28 which will be three fingers breadth The common Weather-glasses then are fallacious and deceitful unless they be so contrived that the Pressure of the Air cannot affect them which is easily done by sealing them Hermetically and in stead of common Water to put in Spiritus Vini rectificatissimus or the most excellent Spirit of Wine and strongest that can be made It may be here inquired whether or not Mercury would ascend in this Glass as the Water does I answer it would because the ascent depends only upon the Pressure of the Air incumbing upon the stagnant Liquor in the Vessell that 's able to drive up Mercury as well as Water It may be inquired secondly how far Mercury will ascend and how far Water will creep up I answer Mercury can ascend no higher in a Tub than 29 inches and Water no higher than 34 foot and this onely happens when there is no Air above the tops of the Cylinders to hinder their ascents But when there is Air as G F above the liquor it can go no higher than the point to which the cold is able to contract the inclosed Air which is in this Glass the point F. It may be inquired thirdly which is the greater difficulty whether or not Mercury will rise as easily in a Tub as Water for seeing it s 14 times heavier it seemes the Air should have greater difficulty to press it up than to press up Water I answer 't is greater difficulty for the Air to press up 20 inches of Mercury than to press up 20 inches of Water yet it s no greater difficulty for the Air to press up 20 inches of Mercury than to press up 23 foot of Water because the burden and weight is the same It may be inquired fourthly whether or not it be as easie for the Air to press up a thick and gross Cylinder of Water as to press up a thin and slender one For example whether is it as easie for the Air to press up a Cylinder of Water 10 inches in Diameter and 10 foot high as it is to press up one two inches in diameter and 10 foot high I answer there is no more difficulty in the one than in the other and the reason is because Fluid bodies do not counterpoise one another according to their thickness but only according to their altitude according to the fourth Theorem Therefore seeing the slender Cylinder is as high as the grosser it must be no more difficult to the Air to press up the one then the other There is one difficulty yet remaining which is truely the greatest of all namely what 's the reason why its more difficult to the Air to press up 20 inches of Mercury than to press up 20 inches of Water or more difficult to the Air to press up 20 inches of Mercury than to press up 10 I answer this comes to pass because the Air is more burthened with 20 inches of Mercury than with 10. Now if this be then surely it must be more hard to the Air to do the one than to do the other even as it is more hard for a man to lift up from the ground 20 pound of iron than to lift up 10 or 15. The case may be better illustrated after this manner Suppose a man standing on the ground with a rope in his hand coming down from a Pulley above drawing up a weight to the top of the house put the case likewise the weight be a stone of 20 pound and the weight of it to increase successively as it is pulled up Now its easie for the man to pull up the stone the first fathom because it is but 20 pound weight but the stone becoming 40 pound in the second fathom and 60 in the third and
an equipondium there is no Pressure in them at all For answer consider first that in all counterpoises there are necessarily two things the movens and the motum the thing that moves and the thing that is moved Secondly you must consider the motum to have a ponduâ— or weight in it and the movens to have a potentia or power wherewith it moves that weight Thirdly that as the thing that moves hath a power or force in it self whereby it moves so the thing that is moved hath a power or force in it self whereby it resists the motion Fourthly that sometimes the resistance of the thing moved may exceed the power of the movent as when a Quarrier with a Leaver endeavours to prize up a stone too heavy for him or the power of the movent may exceed the resistance of the weight or both may be of equal power Consider fifthly that as the pondus of the thing moved begins to grow more and more so the power of the movent decreaseth proportionably not absolutely as heat is extinguished in Water by the cold Air when it is removed from the Fire but respectively For example when a man holds a ballance in his hand with six pound in the one scale and but one pound in the other if you add another pound the weight grows more and the power and force of the opposite scale grows less proportionably not absolutely for it still remains six pound but respectively that 's to say six pound is less in respect of four than in respect of five or the resistance of six pound is less two counterpoising it than being counterpoised by one When a third is added the weight grows yet more and consequently the resistance of the opposite scale becomes yet less till by adding the sixth and last pound you augment and encrease the pondus to that same degree of strength that the resistance of the opposite scale is of From these considerations I say the surface of Air F G hath not lost all its Pressure absolutely by raising the Mercury from G to H but only respectively because it still retains 29 degrees of force in it self I say respectively because when the Mercury is raised ten inches the power of the Air which is of 29 degrees of force is less in respect of ten ounce then in respect of five or the power of 29 degrees of force is less being counterpoised by ten ounce than being counterpoised only by five And when it is raised 20 it is yet less in this respect than in respect of ten And when it has raised the Mercury to the greatest altitude H it may be said to have lost all its Pressure seing it is not able by vertue of a counterpoise to do any more Even as six pound in this scale may be said to have lost all its resistance and weight by putting in the other scale first one pound next two pound and then three pound till the last be put in at which time it hath no more resistance Though this be yet it still remains six pound Even so the Air F G still remains of the same force and power while it suspends the Mercury G H that it was of before Likewise the Pillar A B cannot be said to have lost all its pressure absolutely by falling down from A to C but only respectively because the said Pillar C B is still 29 ounce weight I say respectively because in falling down ten inches or in losing ten ounce the weight that 's now but 48 is less in respect of 29 than while it was 58. It is yet less when it hath fallen down other ten because being now but 38 it must be yet less in respect of 29 than 48. And when it hath fallen down to C 29 it may be said to have lost all its weight because it can do no more having respectively lost all its Pressure From what is said we see a clear ground to distinguish in Fluids a pondus and a potentia Secondly that the potentia may sometimes exceed the pondus and contrariwise the pondus may exceed the potentia Thirdly that inequality of weight between the pondus and the potentia is the cause of motion of Fluids Fourthly that the motion never ceaseth till the pondus and the potentia become of equal force This conclusion is not so universal as the rest because the motion may sometimes cease before this be For example when the Air is pâ—â—â—â—ing Mercury up thorow a Tub shorter then 29 inches the motion ends before there be a perfect counterpoise for 20 or 15 inches of Mercury can never counterballance the force and power of the Air. In such a case then there is an unequal Pressure the Air pressing the Mercury more than the Mercury doth the Air. EXPERIMENT VIII Figure 12. TAke the Vessel A B C D and fill it with Water as high as H I. Take next a Cylinder of stone F G and drowning the half of it among the Water suspend it with a chord to the beam N O with a ring at E. Now in this case though the stone do not touch the bottom of the Vessel yet the Water becomes heavier than before For discovering the true reason of this I suppose first the weight of the Water before the stone be drowâ—ed to be 40 pound I suppose next that after the stone is drowned the said Water to weigh 50 pound And lastly the stone to weigh 60 pound I say then the Water must be 10 pound heavier than before because it supports 10 pound of the stone 'T is certain the beam is less burdened by 10 pound than before If this be then surely the Water must sustain it It were great temerity and rashness to averr that neither the Beam nor the Water sustains it which is really to say it is sustained by nothing It cannot be said without ignorance that 10 pound of the stone is evanished and turned into a Chimera If it be said how can such a Fluid Body as Water be able to support any part of the weight of the stone that is such a heavy Body I answer there is here no difficulty for if the imaginary surface K L upon which the 10 pound of the stone rests be able to sustain 10 pound of Water I suppose the stone taken away and the place of it filled with Water then surely it must also be able to sustain 10 pound of the heaviest metal seing ten pound of Lead or Gold or Stone is no heavier than 10 pound of VVater If some say this rather seems to be the reason why the Water becomes heavier after the stone is drowned because it possesseth the place of as much Water as would weigh 10 pound not as was said because the VVater supports 10 pound of it Therefore it may be judged and thought that if the space that the stone occupies were filled with Air or some light Body without sensible weight the VVater would become heavier than before
We see secondly that this Pressure is according to Arithmetical Progression as 1 2 3 4 5. because in going down the first 14 inches the Mercury rises one inch in going down the second 14 inches it rises two in going down the third 14 inches it rises three and so forward We see thirdly though a VVater were 100 fathom deep yea 1000 yet the Pressure of the Air above is found at the bottom for supposing this Experiment were 100 fathom deep yet would the Air from above have influence upon it to sustain so many inches of the Mercurial Cylinder A Diver then 10 or 15 fathom under the VVater must be burdened with the weight of the Air as well as with the weight of the VVater so must the Fishes though never so deep We see fourthly that the parts of a Fluid cannot cease from motion so long as there is an inequality of weight between the pondus and the potentia This is clear from the falling down of the Mercury from H to G. And assoon as equality of weight happens the motion ends This is clear from the Mercurie's halting at G. Fifthly that in Mercury as well as in Water or Air surfaces may be distinguished and that these surfaces are endowed with a Potentia or power begotten in them by superior and extrinsick weight This is clear from the imaginary surface D C E that 's made powerful to support 58 inches of Mercury in the Tub and that by the weight and Pressure of the Air resting upon A B. Sixthly that as two Fluids differ in specifick and natural weight so they differ in altitude when they counterpoise one another This is clear from the disproportion that 's between the altitude of the Mercury suspended and the height of the Water and Air suspending G F then is 29 inches and the deepness of the Water from K to N is 34 foot because Water is naturally 14 times lighter than Mercury F B is likewise 29 inches and the hight of the Air that rests upon the surface of Water is six or seven thousand fathom high because Air is 14000 times naturally lighter than Mercury Seventhly that Fluid Bodies counterpoise one another not according to their thickness and breadth but only according to their altitude This is evident for though this Tub were never so wide or narrow yet the altitude of the Mercury is unchangeable Hence it is that the thickest Pillar of Water in the Ocean is not able to suspend more Mercury than the slenderest I mean as to altitude And hence it is that the smallest Cylinder of Mercury no thicker than a silk threed is able to counterpoise a Pillar of Water of any thickness whatsoever We may conclude lastly that when a Diver is 20 fathom under the Water he is under as much burden as if he were under 14 or 15 foot of Quick-silver Suppose a man lying on his belly within a large Vessel and 14 or 15 foot of Mercury poured in upon him surely it may be thought that such a burden were insupportable But put the case the Diver were down 40 fathom then must the burden be doubled This follows because if a Pillar of Water 34 foot high with the weight of the Air superadded be as heavy as 58 inches of Mercury then surely a Pillar 20 fathom high or 100 foot must be as heavy as 170 inches which is more than 14 foot EXPERIMENT X. Figure 14. AGainst the former Experiment there occurres some difficulties which must be answered As first if it be the Pressure of the Water that sustains the Mercury in the Tub see the 13. Figure then the weight of the said Mercury ought not to be found while the Tub is poiâ—ed between a mans Fingers But so it is that when a Diver grips the Tub about the middle and raises it a little from the bottom of the Vessel he not only finds the weight of the Tub it self but the weight also of the 58 inches of Mercury that 's within it But this ought not to be if the said Mercury be sustained by the outward Water In a word it ought not to be found because the said Pillar of Mercury as really stands and rests upon the imaginary surface D C E as a Cylinder of Brass or Stone rests upon a plain Table of Timber or Stone If then it be supported by the said surface why ought I to find the weight of it when I lift up the Pipe a little from the bottom of the Vessel For clearing this difficulty consider that when the Mercury falls down from H to G it leaves a soâ—â— of vacâ—ity behind it wherein there is neither Air nor Water Consider secondly that for this cause there happens an unequal Pressure the top of the Tub without being burdened with the Pillar of Water I H which actually presseth it down and nothing within between G and H that may counterballance that downward Pressure These things being considered I answer to the difficulty and say it is not the weight of the suspended Mercury that I find but the weight of the Pillar of Water I H that rests upon the top of the Tub. If it be said the Pressure of a Fluid is insensible and cannot be found I answer it 's true when the Pressure is equal and uniform but not when the Pressure is unequal as here If it be asked how comes it to pass that the Pillar of Water I H is exactly the weight of the 58 inches of Mercury I answer besides the said Pillar there is another of Air that rests upon the top of it which two together are exactly the weight of the suspended Mercury I H being of the same weight with the Mercury G F and the foresaid Pillar of Air being of the same weight with the Mercury F B. To make it more evident remember that one inch of Mercury is exactly the weight of 14 inches of Water and that one inch of Mercury is of the same weight with 14000 inches of Air. If this be then must the Pillar of VVater I H that 's 34 foot high and of the same thickness with the 29 inches of Mercury G F be of the same weight with it seing 29 inches are to be found 14 times in 34 foot For the same reason is the Pillar of Air namely S I that rests upon the top of the Pillar of VVater I H of the same weight with the 29 inches of Mercury F B. For after a just reckoning you will find that 29 inches will be found 14000 times in the Pillar of Air that rests upon the Pillar I H. Or in a word the hight of the Air is 14000 times 29 inches But here occurrs another difficulty Let us suppose there were a Tub six foot high one inch wide having the sides 3 inches thick Imagine likewise the said Tub to be under the water 34 foot with 58 inches of Mercury in it as is represented in this 14 Figure This being supposed the Pillar of Water E A F
take out from L 27 ounce for making a new counterpoise And lastly the Scale K must support the whole weight of the Water H I which is 39 ounce nothing remaining to counterballance this downward Pressure and consequently to ease the Ballance How then is it counterpoised For clearing this you must remember that this Water that 's really 15 foot deep must be reckoned as I said 49 because of the Pressure of the Air upon the top that 's equivalent to 34. If then it be so it cannot raise Mercury higher in a Tub than 42 inches the one being 14 times heavier than the other so that if 14 inches of Water cannot raise Mercury higher than one inch 49 foot cannot raise it higher than 42 inches for as 14 inches are to one inch so is 49 foot to three foot and an half which is 42 inches Now I say the whole weight of the Water H I rests upon the top of the Tub and so presseth down the Scale K to which you must imagine this Tub knit by a string as the former was nothing remaining to counterpoise this downward Pressure for the top of the Mercurial Cylinder being raised as high within the Pipe as the surface of Water D G S is able to raise it the said top can impress no force upon the Tub within to thrust it up and so to ease the Scale K. For example when a man erects upon his hand a Cylinder of Timber or any such like thing which is the outmost he can support he will not be able to impress any impulse upon the seiling of a room above his head but if so be in stead of that taken away there be one lighter erected which he is able to command he can easily thrust up the seiling at his pleasure Just so it is here for the 42 inches of Mercury being the outmost that the surface of Water D G S is able to bear it cannot impress any impulse therewith upon the top of the Tub within but easily can the Cylinder D E impress an impulse and more easily the Cylinder A B seing they are lighter and so more powerful To evidence this a little more let us imagine two things first the Tub G H to be empty as if vacuity were in it In this case the top of the Tub ought to bear the whole burden of the Water and consequently the Ballance to bear it also because there is not a potentia within the Tub to counterpoise this pondus Next let us imagine the Tub to be only full of Water according to this supposition the Ballance cannot be in the least part burdened because the Water within the Pipe presseth it up with as much force as the Water I H presseth it down and if any thing should burden the Ballance it would be only the weight of the Pipe that 's not considerable From what is demonstrated we see first that though this Experiment would seem to prove at the first that a heavy Body weighs as much in the Water as it doth in the Air because the whole weight of the Mercury A B is found in the scale L yet 't is not so because the 14 ounce of Stone L doth not counterpoise any of the Mercury A B but 14 ounce of the Pillar of Water B C. Secondly there 's here a clear ground for asserting a pondus and a potentia in Fluids because this Tub A B is prest down with the VVater B C and prest up with the Mercury within it Thirdly there 's here a clear ground for asserting the Pressure of VVater even in its own place because the Water B C counterpoises by it's weight the 14 ounce of Stone L. Fourthly we see an excellent way for finding the weight of any Cylinder of Water for whatever be the weight of the Mercury in the Tub the Cylinder of Water that rests upon the top will be of the same weight exactly this is evident in comparing the weight of the Mercury G H with the weight of the Water H I. Fifthly that whatever be the height and weight of a Pillar of Water yet the Ballance can sustain no more of it than the just weight of the Mercury this is also evident because the scale of the Ballance supports no more of the weight of the Water B C than the just weight of the Mercury A B. We see sixthly the further down a Pipe with Mercury goes through Water the greater is the Pressure it makes upon the top of the Tub within for put the case this were 100 foot deep the Mercury G H that wants all upward Pressure now would press up the Tub with 40 ounce the Mercury D E with 55 and the Mercury A B with 70. We see seventhly the shorter a Cylinder of Mercury be it is the stronger in pressing and longer it be it is the weaker for there 's more strength in A B than in D E. We see eighthly that the strength decayes and grows according to Arithmetical progression as 1 2 3 4 because if you make the Cylinder G H 41 that 's now 42 it presseth up with one ounce Make it 40 inches it will press up with two ounces of weight Make it 39 it presseth up with three And contrariwise make the Cylinder D E 29 inches that 's now but 28 it will press up with 11 ounce only VVith 28 it presseth up with 12. Make it 30 inches high it will press up with 10. If it be 31 inches it presseth up with nine and so forward Lastly make the Cylinder A B 15 inches that 's now but 14 it presseth up with 26 with 14 it presseth up with 27 make it 16 it presseth up with 25 make it 17 it presseth up with 24. We see ninthly that in Fluids we may make a distinction between a sustentation and an equipondium 'T is evident here because there 's a perfect equipondium between the 42 inches of Mercury G H and the outward Water that 's 49 foot deep But 't is not so between the said Water and the Mercury D E because the said Water is able to raise the said Mercury 14 inches higher therefore the Water only sustains the Mercury D E but counterballances the Mercury G H. We see tenthly that the pondus of the pillar of Water B C is counterpoised by two distinct powers really The one is the 14 ounce of Stone in the scale L the other is the 14 inches of Mercury A B that as really thrusts up the Water as the scale K pulls it up by vertue of the opposite weight Eleventhly take away the Stone L and you will find the Pipe with the Mercury A B sink down this happens not because the surface of Water on which it rests is not able to sustain it but because the 14 ounce of the Water B C that was supported by the Stone doth now press it down Twelfthly the more a Body is unequally pressed by a Fluid the more of the weight of that Fluid is
sensible and the more equally a Body is pressed the less sensible is the weight of that Fluid this is evident because there 's a greater weight of the VVater H I found in the Ballance it takes 42 ounce to counterpoise it than of the VVater E F which is counterpoised with 28 ounce and the reason is because the top of the Tub H supports the whole 39 ounce of VVater H I the Mercury within the Tub not being able in the least to counterpoise it or thrust it up But because the Tub D E is more equally pressed the VVater E F presseth down with 40 and the Mercury D E presseth up with 12 therefore less weight of the VVater E F burdens the Ballance only 28 ounce Hence it is that because the Tub A B is more equally pressed than either D E or G H there 's less of the weight of the VVater B C found in the Ballance only 14 ounce Thirteenthly if in the instant of time while the Tubs are thus suspended in the VVater the Pressure of the Air above were taken away and annihilated then first the 42 inches of Mercury G H would fall down to about 13 inches Secondly the 28 inches of Mercury D E would fall down to as many And lastly the 14 A B would sink down to the same height The reason is because the Pressure of the Air being equivalent to 34 foot of VVater no more would remain but 15 foot which is the real height according to Z M. But 15 foot of Water cannot sustain moe inches of Mercury than about 13. And consequently first 14 ounce of Stone in the Ballance would counterpoise the whole Water B C. The reason is because the Water B C is but of 14 ounce and the Mercury A B being but 13 inches high could impress no impulse upon the top of the Tub within that 's 14 inches high Secondly 13 ounce of Stone in the Scale L would counterpoise the whole Water E F seing E F is but 13 ounce Thirdly the same weight one ounce being deduced would counterpoise the Water H I because in this case it weighs but 12 ounce To proceed a little further imagine the Pipe G H to be suspended by the ballance as the Pipe A B is and then a little hole opened in the top H to suffer the Water to come in till the Mercury subside 14 inches namely from Q to O imagine this Tub to be the other and then stop it The reason why the VVater rusheth in and presseth down the Mercury is the force and Pressure of it for the said VVater finding the Cylinder in equilibrio with the outward VVater presently by its own weight casts the scales which is easily done seeing the surface G S M supports as much burden as it can But that which is more considerable is this after the subsiding of the Mercury from Q to O the equilibrium that was between the scale of the ballance and the VVater Q R is destroyed for whereas 42 ounces were required before 29 will now do it For understanding the reason of this consider that between Q and O are 14 inches of VVater rushed in which are equivalent to one inch of Mercury Next according to former reasonings the ballance must support 29 ounces of the VVater Q R because in this case the top of the Pipe within is pressed up with the weight of 13 ounces which in effect diminisheth as much of the downward Pressure of the VVater R Q which before had the burden of 39 ounces But why is the Tub prest up with 13 ounces I answer because the Mercury that before was 42 inches is now but 28 or having the 14 inches of Water Q O above it it is 29 therefore being shorter the surface G S M is the more able to Press it up even with as much more force as it is in inches shorter In the second place let in as much Water more as will depress the Mercury other 14 inches namely from O to P. In this case 16 ounce of stone will make an equipondium because the 14 inches of Mercury P S and the 28 inches of Water P O Q being a far lighter burden by 26 than the 42 inches of Mercury the surface G S M must be far abler to press them up now than before and therefore must diminish as much of the downward Pressure of the VVater Q R that burdens the Ballance as themselves wants of weight seing then the whole Cylinder of Mercury and Water together are but equivalent for weight to 16 inches of Mercury the top of the Tub within must be prest up with 26 ounce and therefore they by their upward Pressure must diminish 26 ounce of the weight of the Water R Q that weighs 39. Lastly let in so much VVater as will depress the last 14 inches P S and you will find no more weight required in the Ballance to make an equipondium than counterpoiseth the simple weight of the Tub which is not considerable The reason is because the part S of the surface G S M being liberated of the burden of Mercury and sustaining only the VVater within the Tub in stead of it this surface presseth up the VVater within the Tub and consequently the top of it with as great force and weight as the top of the Tub without is depressed with the outward VVater R Q therefore 39 ounce depressing the Tub and 39 ounce pressing it up the Ballance must be freed of the whole weight of VVater R Q. If it be objected that the 42 inches of VVater Q S are equivalent in weight to three inches of Mercury therefore the part of the surface S being burdened with this cannot press up with as great force as the VVater R Q presseth down For answer consider that the part S is able to support 42 ounce of VVater and next that the VVater R Q weighs but 39. Then I say seing the 42 inches of VVater within the Tub weighs only three ounce the part S that 's burdened therewith being able to support 42 it must press up with the weight of 39 and so counterballance the VVater R Q. If it be inâ—uired whether or not would the 14 inches of Mercury A B fall down a small hole being made in the top of the Tub at B I answer they would If it be objected that these 14 inches of Mercury are not in equilibriâ— with the Pressure of the ambient Water as the Mercury G H and therefore they cannot be so easily depressed by the Water that comes in at the said hole I answer they must all fall down and as easily as the other and that because of inequality of weight between the Potentia of the surface of VVater and the Pondus It 's certain the part A of the surface cannot support more weight of any kind than 42 ounce but when a hole is opened in B and the VVater coâ—es in 't is then burdened with the weight of 14 ounce of
far narrower diameter with an orifice H. There is also an orifice at L with a neck about which is knit a small chord M L for letting down this Engine to the bottom of the VVater A B. For trials cause fill the wide glass with Mercury from P to K and you will find it rise in the narrow Pipe as high as the orifice H. This being done close hermetically or with good cement the orifice L then by help of this chord let all go down from the surface C D till it be exactly 17 foot from the top and you will find the Mercury thrust down in the narrow Pipe from H to R 14 inches and an half Let it down next as much and the Mercury will be yet further thrust down namely from R to N the part H R N being full of Water For understanding the reason of this consider that between N and E are 34 foot for so high is the slender Pillar of Water that comes from the top and entring the orifice H comes down thorow the Pipe to N. Consider next that between the said Pillar of Water and the Mercury N P K there is a counterpoise but this counterpoise cannot be unless the Pillar of Water be 34 foot high seing between N and K are 29 inches of Mercury for each inch thereof requires 14 of Water Upon this account it is that when the glass is 17 foot drowned 14 inches and an half are thrust down from H to R. If it be objected that the Pressure and Bensil of the inclosed Air I K is equivalent to the weight of other 29 inches and therefore the Pillar of Water E H R N must be 68 foot high before a counterpoise can happen I answer 't is true that 's said but you do not consider that there is a Pillar of Air F E resting upon the top of the Pillar of Water that makes a compensation exactly To speak then truely and really the 29 inches of Mercury N P K have the weight of 58 inches and the 34 foot of Water E H R N have the weight of 68 foot For a third trial let down the glass 6 foot further and you will find the Water pierce up thorow the thick Cylinder of Mercury P K and rest upon the top K. The only difficulty is to determine how much will spring up before the motion of it cease 'T is evident that the Water will ascend because coming to the Base of a thick and gross Cylinder that it cannot intirely lift it must pierce thorow it seing the force of such a Pillar of Water is now much stronger than the Mercury for in effect the glass being drowned 6 foot further the Pillar that comes down thorow the slender Pipe hath the just weight of 34 inches of Mercury but 29 cannot resist 34 therefore the Water not being able to lift it by reason of the disproportion that 's between the thickness of the one and the slenderness of the other it must pierce up thorow it For clearing this difficulty consider that this glass cannot go down from one imaginary surface to another v. g. from 34 foot where it was till it come to 40 where it now stands but there must be an alteration in the equipondium seing by going down the Pillar of Water E H R N grows higher and consequently heavier and therefore some VVater must pierce up thorow the Mercury for making a counterpoise for 't is impossible for two Fluids to counterpoise one another unless they be in equilibrio Consider secondly that after the Water is come to the top of the Mercury at K it will find difficulty to find a room for it self seing the space between S and I is full of Air. Notwithstanding of this it must ascend I say then after the glass is gone down from 34 to 40 foot there will be about four inches of VVater above K which have reduced the 29 inches of Air K I to 25 S I. If it be asked between what two things is the equipondium now I answer the first was at R between E H R and R N P K. The second was at R between N R H E and N P K. The third is now at S between the 25 inches of inclosed Air I S as one Antagonist and the four inches of Water S K with the 29 inches of Mercury K P and the Water P N R H E as the other To make a fourth equipondium sink the Glass other six foot till it be 46 foot from the top C D then must some more VVater spring up thorow the Mercury this of necessity must be seing the Cylinder of VVater N R H E is six foot higher and so far heavier than it was if this be then must the 25 inches of Air I S be reduced to less quantity seing 'tis impossible for one Fluid to become heavier unless its opposite and antagonist become heavier too for an equipondiums sake Note that the Air I S will not lose other four inches with this six foot of VVater as it did with the former The reason is because if for every six foot the Glass goeth down the Air were comprest four inches it were easie at last to reduce it to nothing for if six reduce it to four and 12 to eight 38 ought to reduce it to no inches which is impossible Therefore I judge it must suffer compression by a certain proportion as we see upon a Scale the divisions of Artificial or Natural Sines grow less and less there being more space between 1 and 2 than between 2 and 3 more between 2 and 3 than between 3 and 4 and so upward till you come to 90. Therefore the second six foot must reduce the 25 inches not to 21 but to 23 circiter and so forth By the which means though the Glass should go down in infinitum yet the Air shall never be reduced to nothing and there shall still some small quantity of VVater come up Or in such a case the Air may be so comprest that it can be no more all the disseminate vacuities being expelled But suppose this to be at 1000 fathom then at 1500 where the Pressure is stronger there can be no equipondium which is absurd for where the pondus becomes stronger the potentia ought to grow stronger likewise I answer the motion of condensation ceaseth indeed but there still remains a potentia or rather in such a case a perfect resistentia whereby the Air is able to resist the greatest weight imaginable before it can be reduced to nothing or suffer a penetration of parts that 's to say two parts to be in one space From the explication of these Phenomena we conclude first that in Water there is a considerable Pressure seing in letting down the Glass 17 foot the Mercury is prest down from H to R and from R to N in going down other 17 foot Secondly that 29 inches of Mercury are as heavy as 34 foot of VVater because the Mercury
Air comes out The reason is the same namely less Pressure in E than in F therefore when the inclosed Air that hath five degrees of Bensil comes to E that hath but four it must overcome and so long must it be victorious till by expanding it self it be reduced to the Bensil of four In pulling up the Glass from E to D more Air yet breaks out because a surface of three degrees of Pressure is not able to resist four degrees of Bensil In passing from D to C more Air comes yet out for the same reason till in going up to the top where there is no Pressure no more Air breaks out 'T is to be observed first that the motion of the Air up thorow the Water is but slow the medium being thick and gross Secondly that if the Glass be pulled up quickly from one surface to another or contrariwise let down quickly it presently breaks in pieces This comes to pass through the strong Bensil of the inclosed Air that must have time to expand it self otherwise it breaks out at the nearest for it being of six degrees of Bensil and coming quickly to a surface of five there happens an unequal Pressure the sides of the Glass being thrust out with greater force than they are thrust in with But if so be the Glass move slowly up the inclosed Air gets time to thrust it self out by degrees so that whatever surface the Glass comes to there is little difference between the Pressure of the Water and the Bensil of the Air. The reason why the Glass breaks in pieces while it goes quickly down is likewayes unequal Pressure upon the sides for in passing quickly from a surface of five degrees to a surface of six the sides are prest in with greater force than they are prest out with and the reason is because through the straitness of the hole G the Water cannot win in soon enough to make as much Pressure within as there is without 'T is to be observed thirdly that if the orifice G be stopped before that the Glass be sent down it will not go beyond three or four fathom when it shall be broken in pieces though the motion were never so slow and this comes to pass through the strong Pressure of the Water Fourthly the stronger the Glass be in the sides it goes the further down without breaking therefore a round Glass Bottle will sink 20 or 30 fathom before that it be broken with the Pressure of the Water If a Vessel of iron were sent down it ought to go much further An empty Cask or Hogshâ—ad will not sink beyond seven or eight fathom without breaking or bursting yet a Bladder full of wind knit about the neck with a Pack-Threed will go down 100 fathom yea 1000 without bursting It may be here inquired what sort of proportion is keeped by the unequal ingress of the Water I answer it may be known after this manner Let first down the Glass one fathom and having pulled it up again measure the deepness of the Water in the bottom of it Next having poured out that Water let it down two fathom and pulling it up measure the deepness which you will find more than afore Do after this manner the third time and the fourth time till you come to the lowest fathom and you will find the true proportion From what is said we see first that in Water there is a Pressure because through the force and power of this Water the 12 inches of Air that filled the Glass are reduced to three Secondly that this Pressure growes as the Water growes in deepness because there is more Pressure in B than in A more in C than in B and Io downward Thirdly that when Air is comprest by some extrinseck weight the Bensil is intended and grows stronger by unequal proportion as is clear from the unequal divisions 1 2 2 4 5 6. Fourthly two Fluids cannot cease from motion so long as the potentia of the one is unequal to the poâ—dâ—s of the other this is evident from the Water 's creeping in at G all the while the Glass is in going down and from the Air 's coming out all the while the Glass is in coming up Fifthly that no sooner two Fluids come to equality of weight but as soon the motion ends because if the Glass halt at D E or F in the going down upon which follows a counterpoise then doth the creeping in of the Water cease Sixthly there may be as much Pressure in a small quantity of a Fluid as in the greatest because there is as much Bensil in the small portion of Air included between K and G as there is of Pressure and weight in this whole Water that 's 30 fathom deep Seventhly that the Pressure of a Fluid is a thing really distinct from the natural weight this is evident from the Pressure of the inclosed Air G K that 's more and less as the Pressure of the Water K M is more and less but the natural weight is still the same seing the same quantity remains Eighthly one part of a Fluid cannot be under Pressure but the next adjacent must be under the same degree of Pressure this is also clear because what ever degree of bensil the included Air K G is under the Water K M is under the same Therefore when the one is under six as in the lowest fathom the other is under six likewise And when the one is under five degrees of Pressure as in the surface F the other is under as much Ninthly Bensil and Pressure are equivalent to weight because the Water K M is as much burdened with the Bensil of that small portion of Air above it as if it had a Pillar of Water 30 fathom high upon it Tenthly that the Pressure of Fluids is most uniform and equal and that two Fluids of different kinds may press as uniformly as if they were but one this is evident from the sides of the Glass that are not broken in pieces by the strong Bensil of the inclosed Air and heavy Pressure of the inclosed Water and this happens because the Pressure without is as strong as the Pressure within We see lastly that Water does not weigh in Water because when a man lets down this Glass by the chord to the lowest surface he finds not the weight of the Water K M that 's within the Glass but only the weight of the Lead Q. 'T is certain he finds not the weight of the Water I H because it rests not upon the Glass within but is sustained by ' its own surface the mouth of the Glass being downward and open When I say Water does not weigh in Water the meaning is not that Water wants weight or Pressure in it but that this weight and Pressure is not found as the weight and Pressure of other bodies are found while they are weighed in Water For example a piece of Lead or Gold hung in the Water by a
not contract it self no difference would happen but this is impossible so long as the Water is under a Pressure The expedient then must be found out another way namely by kniting a small rope to the iron ring N in length with the other to which at certain distances relating to the fathoms the Ark goes down must be fastned empty little Vessels of Wood or bladders which by their lightness may compense the decrement and decreasing of the Air. First then let down the Ark three fathom and see how much it is heavier than before and as you find the difference so fasten to R one Bladder or two till the Ark be brought near to a counterpoise Secondly let it go down other three fathom and observe that difference also and accordingly fasten to T as many as will reduce the two to a counterpoise again Do after this manner till it sink 15 or 20 fathom 'T is to be observed that the further down the Ark goes the difference is the less therefore less addition will serve and the reason is because there is less Air contracted in passing between the fifth and the tenth fathom than in passing from the first to the fifth The proportion of contraction is represented by the unequal divisions within the mouth of the Ark as 1. 2. 3. 4. In a word by what proportion the decrement of the Air is by that same proportion must the addition be upon the rope S N. Suppose then the Air to be diminished four inches in going down four fathom which will be 5184 square inches or three square foot then surely as much Air must be added to the rope S N by bladders In going down as far let us suppose three-inches to be contracted then less will suffice Though it cannot be determined without trial how much Air is contracted in three fathom and how much in six and how much in nine yet this is sure that the decreasing is according to unequal divisions that 's to say less in six than in four less in 8 than in six and less in 10 than in 8 and so downward and that this is the rule namely according to what quantity the Air within the Ark is contracted according to that same measure must the addition of Air be to the rope If it be said that Bladders full of wind cannot go down thorow the VVater without bursting I answer 't is a mistake because their sides being pliable and not stiff like the sides of a Timber Vessel they yeeld and therefore cannot burst It 's observable that when a bladder goes far down the sides becomes flaccid and flagging In this case the Air that before had the forme of the Bladder and was somewhat ovall must now become perfectly globular and round for 't is sure that the dimensions of it are altered by the Pressure of the VVater namely from more quantity to less if this be then the form must be round seing the Pressure of the Water is most uniform even as drops of VVater or Rain from a house side are round upon this account This second way may be thought upon also Make the Leaden foot-stool that sinks the Ark not of one piece but of many that so when the Air within it begins to be contracted by degrees in going down a proportionable weight may be subtracted for keeping a just counterpoise all the while of the descent Or because the greatest trouble is in bringing of it up let the Diver when once he is at the bottom subtract so much weight from the foot-stool as he thinks will go near to make a counterpoise at that deepness For example if the weight of the foot-stool be 40 pound heavier than the Ark then let him subtract 30 or 36 which may ly and rest upon the ground till it be drawen up at a convenient time by a chord By his means it will be easie to move the Ark from one place to another Next there shall be little or no difficulty to pull it up Nay upon supposition the rope were broken by which it was let down yet if the Diver please he may come up without any mans help And this is most easily done namely by subtracting as much weight as will make the Ark the stronger party 'T is to be observed that when you are at the bottom and if you make the Lead but one pound lighter than the Ark it will surely come up and cannot stop by the way The reason is because a very small weight will turn the Scales between two bodies thus weighing in VVater Next the further the Ark comes up it becomes the lighter because the Air within it expands it self the more But leaving this let us come to explicat the reason why the contraction of the Air is not uniform but rather difform For if in going down three fathom three inches be contracted there will not be other three contracted in going down the second three but less and yet less in going down the third three Two things then are to be explicated here First why there is a contraction Next why it is after such a manner As for the first the contraction is caused by the Pressure of the Water which gradually increaseth from the top to the bottom as is clear from the last Experiment therefore there being a greater Pressure in a surface six fathom deep than in a surface three fathom deep the Air within the Ark must be more contracted in passing between the third and sixth than in passing between the first and third When I say more contracted the meaning is that more quantity is contracted to less whereby the Bensil of it is more intended or that the Air is more bended As for the second we must remember from the last Experiment that the cause of this is not from the VVater as if forsooth the Pressure of it were according to unequal proportion but from the Air it self whose kind and nature it is to suffer compression after such a way 'T is evident in Wind-guns whose second span of Air is comprest with greater difficulty than the first and the third with greater difficulty than the second 'T is so with all bodies endowed with Benfil for ay the longer you bend you find the greater difficulty As there is a great disadvantage to the man that Dives from the contraction of the Air so there is a great advantage to him from this manner and way of contraction for if it were uniform according to the Pressure of the Water then if three fathom comprest three inches six fathom ought to compresse six inches nine fathom nine inches and so forward till by going down either the whole Air should be comprest to no inches or else very little should remain for respiration The next thing to be taken notice of is that all the while during the down going of the Ark there is still equality of weight between the Pondus of the Water and the Potentia of the Air for with what
same bladder and blow it stiff with Wind and knit the neck as afore And you will find that in the up-coming the sides of it will burst asunder with a noise When the Bladder is thus full of Wind 't is supposed that there is a sort of counterpoise between it and the Air of the Ark. But as the Ark ascends the Air of it becomes weaker and weaker while in the mean time the Air of the Bladder suffers no relaxation therefore when the Ark comes near the surface there arises a great disproportion between the one Air and the other as to strength and therefore the Air of the Bladder being the strongest rents the sides in pieces and comes out with a noise Or blow it but half full of wind and you will find before the Ark come near to the top the said Bladder to be bended to the full For a third trial take a Glass such as they use in Caves for preserving of Brandy and stopping the mouth closely take it down with you in the Ark and you will see the sides of it break in pieces before you go down four or five fathom The strong Bensil of the ambient Air is the cause of this If you take it down with the orifice open no hurt shall befal it Or if you stop the orifice in the up-coming you will find the same hurt come to it But here is the difference in the first bursting the sides are prest inward by the ambient Air in the second the sides are prest outward by the Air within the Glass For a fourth trial take a round Glass-bottle pretty strong in the sides and when it is down with you in the Ark 14 or 15 fathom stop the mouth of it exactly and when it comes above you will find a considerable quantity of Wind come out of it when the orifice is opened This evidently demonstrats that the Air within the Ark 12 13 or 14 fathom down is under a far stronger Bensil then the Air above For a fifth trial let a man apply to his skin a cold Cupping-Glass when he enters the Ark and he will find such a swelling arise within it as when it is applied hot by a Chyrurgion This tumor begins to rise assoon as the Ark begins to go down The reason is evident from unequal Pressure the parts within the Glass being less prest than the parts without For a sixth trial take a common Weather-Glass and Place it in the Ark and in the going down you will see the liquor creep up in it by degrees as the Ark goes down as if some extraordinary cold were the cause of it And as the Ark comes up by degrees the said liquor creeps down by degrees The cause of this Phenomenon is not cold as some might judge but the strong Bensil of the Air within the Ark that so presseth upon the surface of the stagnant Water that it drives it up If you take with you a Weather-Glass hermetically sealled no such thing will follow because the outward Pressure is keeped off 'T is not then cold that 's the cause but weight By the way take notice that all common Weather-Glases are fallacious and deceitful because the motion of the Water in them is not only caused by heat but by the weight of the Air which sometimes is more and sometimes less as frequently I have observed and as hath been observed by others This difference is found by the alteration of the altitude of the Mercurial cylinder in the Baroscope which is more and less as the Pressure of the Air changeth In fair weather and before it comes the Mercury creeps up In foul and rainy weather and a pretty while before it fall out it creeps down Because in fair weather the weight of the Air is more than in rainy and dirty weather December 13. 1669. I found the altitude 29 inches and nine ten parts of an inch at this time the heavens were covered with dry and thick clouds and no rain followed March 26. 1670. I found the altitude no more than 27 inches and nine ten parts at which time there was a strong Wind with rain Between these two termes of altitude I have found the Mercury move near a twelve moneth 'T is a most sure prognosticator for if after rain you find the Mercury creep up in the morning you may be sure all the day following will be fair notwithstanding that the heavens threateneth otherwayes If after fair weather the Mercury subside and fall down a little you may be sure of rain within a short time though no appearance be in the present It falls down likewise when winds do blow What the true cause is why there is such an alteration in the Pressure of the Air before foul weather and fair and in the time of it it is not easie to determine But we proceed Trial likewise might be made by fiting a great piece of Ordnance above whether the report would be heard below the Water or not This would determine the question whether Water be a fit medium for conveying sound as Air is Item whether or not the Sea water be fresher at the bottom than near the top which is affirmed by some Item whether sounds be as distinct in such a small portion of Air as they are above This might be tried with a Bell of a Watch. If need were a little chamber Bell might be hung within the Ark and a small chord might pass up from it through the cover whereby the persons above might by so many tingles speak such and such words to the Diver I have demonstrated before that though there were a little narrow hole made in the cover above yet neither Air would go out nor Water come in If a man were curious he might have a window not only in the sides but in the roof above covered with a piece of pure thin Glass thorow which he might look up after he is down two or three fathom and see whether there appeared any alteration in the dimensions of the body of Sun or not or seemed nearer EXPERIMENT XIX Figure 26. THis Figure represents a deep Water whose first and visible surface is F G. The imaginary surface is E L C 34 foot below it A D B is a Siphon working below this VVater with Mercury A E L is a Vessel with stagnant Mercury among which the orifice A is drowned the other orifice B existing among the Water D M is the hight of the Siphon above the line of level which I suppose is 58 inches For making it work stop the two orifices closely and pour in as much Mercury at a hole made at D as will fill both the legs Then stopping the said hole open the two orifices A and B and you will find the liquor run as long out at B as there is any almost in the vessel A E L. For evincing this which is the only difficulty consider that if this Siphon were filled with Water and made to work only
with Air as is clear from daily experience the liquor would run out constantly at B. Because there is here an unequal Pressure the surface of Air N B being more burdened than the surface E L C but where unequal Pressure is in Fluids according to the 12th Theorem motion must follow I prove the surface N B to be more burdened than the surface E L C because the Water B D is heavier than the Water L D as is evident to the eye The Air B therefore sustaining far more weight than the Air E L must cede and yeeld Next there is here a pondus and a potentia the pondus is the VVater L D the potentia by which it is counterpoised is the Water B D but these are unequal B D being heavier than L D therefore according to the 33 Theorem these two Fluids cannot cease from motion If it be said that the surface N B is stronger than the surface E L C seing it is lower I answer the difference is so unsensible that they may be judged but one Now I say if this Siphon work in Air with Water it must likewise work in Water with Mercury Therefore this Siphon being 34 foot below the first surface F G the liquor must run out constantly at B. Because there is here an unequal Pressure the surface of VVater N B beâ—ng more burdened than the surface E L C. Though there be more weight in N B than in E L C because it is lower yet because the difference is not so much as is between the weight of B D and the weight of L D it proves nothing Note here that so long as D is within 58 inches of E L C this Siphon will work The reason is because the Pressure of 34 foot of VVater with the Pressure of the Air upon F G are able to raise Mercury exactly 58 inches But if D exceed that hight no Art will make the liquor run out at B. Note secondly that this Siphon will operate with Air and VVater though the top D were 34 foot above M and the reason is because the Pressure of the Air is able to raise a pillar of Water to that hight Note thirdly that if there were an orifice opened at C upon the level line E L C the two Waters would become of the same weight the one not being able to move the other If you bore a hole at R the liquor ascends from R to D and goeth down from D to A and so the motion ends But if the leg A D were six times wider than B D the liquor would not run out at B. I shall answer this in the close From this Experiment we see first that the motion of Fluid Bodies up thorow Pumps and Siphons is not for shuning vacuity but because they are prest up violently We see next that when the Pressure is uniform there is no motion in Fluids but assoon as one part is more prest than another motion begins because this Siphon will not operate if the orifice be made in C but if so be it be in D then the motion begins because there is here an unequal Pressure which was not in the other We see thirdly that Fluids have a determinate Sphere of activity to which they are able to press and no further because this Water is not able to press Mercury higher than 58 inches So the Air cannot raise Water higher than 34 foot If this Water were 68 foot deep the Sphere of it's activity would be 116 inches We see fourthly that in Fluids there is a Pondus and a Potentia and that the inequality of weight between the two is the only cause of motion We see fifthly that as long as this inequality of weight continues as long continues the motion because as long as B D is heavier than L D the motion perseveres We see sixthly the possibility of a perpetual motion in Fluids because the liquor runs perpetually out at B. If it be said the motion ends when the stagnant Mercury A E L faileth I answer this stop is only accidental and not essentially from the nature of Fluids If it be enquired whether or not would the Mercury run out at B upon supposition the shank L D were twice as wide as the shank B D I answer it would If it be said that the one is far heavier than the other namely L D than D B. I answer weight in Fluids is not counted according to thickness but according to altitude EXPERIMENT XX. Figure 27. THis last is for demonstrating the precise and just weight of any Pillar of Air Water Mercury or of any other Fluid body if some of their dimensions be but once knowen A B then is a square Pipe 12 foot high and six inches in wideness full of Water resting upon the surface of Air A C. And E G is a square Pipe 12 foot high and 12 inches wide full of VVater resting upon the surface of Air E F. None needs to doubt but the two Waters will be suspended after this manner even though the orifices A and E were downward especially if they be guarded with Water but the demonstrations will be the more evident that wee suppose the two Pillars of Water to be suspended as they are From this Experiment I say first that the Pillar of Air C D is 168 pound weight at least which I prove thus The VVater A B is 168 pound therefore the Air C D must be as much I prove the Antecedent because it 's a Pillar of VVater 12 foot high and six inches thick but every half cubical foot of VVater that containes 216 inches weighs seven pound therefore seing the Pillar is 12 foot it must contain 24 half feet but 24 times 7 is 168. The only difficulty is to prove the Connexion which I do thus from the seventh Theor. all the parts of a Fluid in the same Horizontal line are equally prest but so it is that the part A and the part C are in the same horizontal surface therefore the part A and the part C are equally prest But if the part A and the part C be equally prest the Pillar of Air C D must be as heavy as the Pillar of VVater A B. I say secondly that the Pillar of Air F H weighs 672 pound I prove it thus The Water E G weighs 672 pound therefore the Air F H weighs as much The Antecedent is clear because E G is a square Pillar of VVater 12 foot high and 12 inches thick but every cubical foot of VVater weighs 56 pound but 12 times 56 is 672. I prove the connexion as before All the parts of an horizontal surface are equally prest therefore the part F must sustain as much burden as the part E. To proceed a little further let us suppose the Pipe A B to be 34 foot high and the Pipe E G to be as much I assert then thirdly the Pillar of Air C D to weigh 476 pound which I prove
as before All the parts of the same surface are burdened with the like weight but the part A sustains 476 pound therefore the part C must support as much The Connexion is evident and the Antecedent is so too because the VVater A B being 34 foot high and six inches thick must weigh 476 pound for if 216 inches weigh seven pound 14688 inches must weigh 476 pound I assert fourthly the Pillar of Air F H to weigh 1904 pound which I demonstrat by the former Medium All the parts of a Fluid that ly in the same horizontal surface are equally prest but so it is that E and F do so ly therefore F must be as much burdened as E the Water therefore E G weighing 1904 pound the Air F H must weigh as much For if 216 inches of Water weigh seven pound 58752 inches for so many are in the Water E G must weigh 1904 pound Let us suppose secondly the Tub A B to be only 29 inches high and the Tub E G of the same hight and that six inches wide and this 12 inches wide I affirm then fifthly the Air C D to weigh yet 476 pound and the Air F H to weigh 1904 pound Because the Pillar of Mercury A B weighs 476 pound and the Pillar of Mercury E G weighs 1904 pound therefore if A B be 476 C D must be as much And if E G be 1904 F H must be of the same weight I prove the Mercury A B to weigh about 476 pound though it be but 29 inches high because it is 14 times heavier than Water For the same cause doth the Mercury E G weigh about 1904 pound I say about because 34 foot containes 29 inches more than 14 times Let it be supposed thirdly the Pipe E G being 34 foot high to have the one half of it I G full of Air and the other half E K full of VVater I affirm then sixthly the part E and the part F to be yet equally burdened That 's to say the VVater E K that 's now but 17 foot makes as great a Pressure upon E as when it was 34 foot The reason of this is surely the Pressure of the Air I G that bears down the Water K E with the weight of 952 pound the half of 1904 pound If it be said according to the Theorem 21 that there is as much Pressure and weight in the least part of a Fluid as in the whole therefore the Air I G must be as heavy as E H. I answer I G is not so heavy as F H because the Water E K impending in the lower part of the Tub hath occasioned the Air I G to expand it self so many inches by which means it loseth so many degrees of it's Bensil If you remove the Water E K then will the Air I G be as heavy as F H because E K being Air it reduceth I G to that same degree of Bensil with it self but when the Air E is burdened with the Water E K it cannot make the Air I G of that same weight with it self Let us suppose fourthly that only eight foot and an half of Water are in the Tub namely between E and N. I say then seventhly that the part E is as much burdened with it as when the Pipe was full because the 25 foot and an half of Air N G is exactly as heavy as the 25 foot and an half of the Water that 's gone I prove it thus The Air E hath the weight of 1904 pound in it self seing the weight of the surface is alwayes equal to the weight of the Pillar but being burdened with the VVater E N that weighs 476 pound it cannot press up with more weight then with 1428 pound and therefore the top of the Water N must press upon the under part of the Air that 's contiguous with it with 1428. If this be the Air N G must press down with as much seing according to the 20 Theorem it is impossible that one part of a Fluid can be under Pressure unless the next adjacent part be under the same degree of Pressure Therefore I conclude that the 25 foot and an half of Air N G is as heavy as the 25 foot and an half of the Water that 's gone This makes it evident also that when the Pipe is half full of VVater as E K the Air I G hath the weight of 952 pound Because E being in it self 1904 but being burdened with E K 952 it cannot make the top of the Water K press upon I with more weight than 952 and therefore by the 20 Theorem the Air G I must weigh 952 likewise I affirm eighthly that when the Pipe is full of Water from E to G if a man poise it in his hand he doth not find the weight of the Water E G. And the reason is because it 's sustained by the part of the surface E. But if the Air E sustain it my hand cannot sustain it I find then only the weight of the Tub but not the weight of the VVater within it I say ninthly that when I poise the said Tub I find the whole weight of the Pillar of Air L M which is exactly 1904 pound I prove it thus The pondus of a Fluid is then only found when there is not a potentia to counterpoise it or at least when the potentia is inferior to the pondus but there is here no potentia counterpoising the pondus of the Air L M. Therefore I must find the weight of it when I lift up the Tub. The major proposition is clear from the tenth Theorem It 's evident also from common experience for while a ballance is hanging upon a nail with six pound in the one scale and nothing in the other you will find the whole burden if you press up that one scale with the palm of your hand But if so be there were six pound in the opposite scale you will not find the first six and the reason is because it is in equilibrio with other six 'T is just so here I must find the weight of the Air L M while I poise the Tub because it wants a weight to counterballance it I prove the minor proposition thus If any thing counterballance the Air L M it must either be the Air below namely the part E or the Water E G but neither of the twain can do it Not the Air E because it hath as great a burden upon it as it is able to support namely the Water E G that weighs 1904 pound And for this cause not the VVater it self seing all the force it can have to counterballance L M is from the surface of Air E but this is in equilibrio with it already I said that the Air L M was exactly 1904 pound weight This also is evident because it is just of these same dimensions with the Air F H. If it be said the Air L M must be thicker seing it's equal to
the Tub without but the Air F H is only equal to the Tub within I answer it is so indeed but here is a solution to the difficulty I do not find the whole weight of the Air L M but only as much of it as is equal to F H. Suppose the Tub to be 12 inches within from side to side and 16 without from side to side I say then I find only the burden of so much Air as answers to the cavity of the Tub because the rest of these inches are counterpoised by as much below namely by the Air that environs the orifice E for it 's supposed that if the Tub be two inches thick above it must be as thick in the lips So that the whole Tub is not unequally prest but only so much of it within upon the top as answers to the cavity Tenthly that when the Pipe is but half full of VVater namely from E to K I find only 952 pound of the Air L M though before I found 1904. The reason is because the one half of it is now counterpoised by the Air I G and therefore the weight of it becomes insensible 'T is clear from the sixth assertion that the Air I G presseth down with 952 therefore it must press up with as much seing according to the sixth Theorem the Pressure of a Fluid is on every side Eleventhly that when there is only eight foot of VVater and a half in the Tub namely between E and N I find only 476 pound of the Air L M. Because in this case the Air N G counterpoiseth 1428 pound of it For if the said Air burden the Water N E with 1428 pound as is clear from the seventh assertion it must likewise press up the Tub with as much and so counterpoise as much of the Air L M. Twelfthly that when there is nothing within the Pipe but Air the whole weight of the Air L M becomes insensible to me The reason is evident because it is wholly counterpoised by the Air within the Pipe I affirm thirteenthly that the VVater E G is in equilibrio with the Water A B that 's to say 1904 pound is in equilibrio with 476 pound I prove it evidently by the first medium all the parts of an Horizontal surface are equally prest therefore the part A sustains no more burden then the part E therefore A B is as heavy as E G and consequently the Air C D must be as heavy as the Air F H. Lest this proposition may seem to contradict what is already said I must distinguish a twofold Ballance according to the third Theorem one Natural another Artificial In the Artificial Ballance where magnitudes do weigh according to all their dimensions viz. Longitude Latitude and Profundity the Water A B and the Water E G are not in equilibrio together seing the one is 1428 pound heavier than the other But in the Ballance of Nature such as these Pipes are all the four makes an equipondium together because they do not weigh here according to their thickness but only according to their altitude Therefore seing A B is as high as E G and seing C D is as high as F H they must all be of the same weight From the first assertion I infer that one and the same Fluid even in the Ballance of Nature may sometimes be in equilibrio with a lesser weight and sometimes with a greater because the Air C D that weighs really 476 pound is in equilibrio with the Water A B that weighs but 168. This is when A B is supposed to be only 12 foot high It 's likewise in equilibrio with it when it s 34 foot high But how can A B that 's 12 foot high press A with as much weight as when it s 34 foot high I answer by a similitude when a Cylinder of Wood 12 foot high stands upon a Table it may burden it as much as if it were a Cylinder 34 foot high For supposing it to be thrust in between it and v. g. the ceiling of the room above it must press down with more weight then if it were not thrust in So this Cylinder of Water A B that 's but 12 foot high being prest between the surface A and the top of the Tub within must burden A as much as if it were 34 foot high for being of this hight it only stands upon the surface without pressing up the top of the Tub. I infer from the second assertion that each Pillar in a Fluid hath a determinate weight This is evident from the determinate weight of A B that weighs first 168 pound being 12 foot high and 467 pound being 34 foot high and so of the rest I infer secondly that the thicker and grosser a Pillar of a Fluid be it is the heavier even in the Artificial Ballance and contrariwise the more slender and thinner it be it is the lighter This is evident from the Water A B six inches thick that weighs 476 pound and from the Water E G 12 inches thick that weighs 1904 pound So doth the Pillar of Air C D weigh less then the Pillar F H. Here is ground for knowing the certain and determinate weight of a Pillar in any sort of a Fluid whatsoever As to Air its clear and evident that a four-square Pillar thereof 12 inches every way weighs 1904. That 's to say if it were possible to take the Pillar of Air F H in its whole length from the surface of the earth to the top of the Atmosphere and pour it into the Scale of a Ballance it would be exactly the weight of 1904 pound Here is a secret though that same Pillar of Air were no longer than 6 or 10 foot yet the Pressure of it upon the body it rests upon is equivalent to 1904 pound If this be you say what is the weight of Air that rests upon this Table that 's 36 inches square I answer it must be as heavy as a Pillar of Water 34 foot high and 36 inches thick which will by just reckoning amount to 17136 pound or to 1071 stone weight It may be inquired next what 's the weight of the Air that burdens the pavement of this parlour that 's 16 foot square I answer 487424 pound Because it is exactly the weight of a bulk of Water 34 foot high and 16 foot thick 'T is to be remembred that though the Pressure of it be so much yet being poured into the scale of a Ballance it will not weigh so much for not only as much as fills the room must be taken but as much as passeth from the pavement to the top of the Atmosphere According to this method 't is easie to determine the weight of any Pillar of Air whatsoever provided a man but once know the thickness of it both the wayes e. g. there 's a planum 12 inches long and six inches broad upon which rests a Pillar of Air. The weight of it then is just the burden of
that most easily OBSERVATION VIII THere hath been much inquiry made by some anent the reason why the dead body of a man or beast riseth from the ground of a Water after it hath been there three or four days But though many have endeavoured to solve the question yet the difficulty remains and in effect it cannot be answered without the knowledge of the foregoing Doctrine anent the nature of fluid Bodies To find out the reason then of this Phenomenon consider that all Bodies are either naturally heavier then Water as Stone and Lead or naturally lighter as Wood and Timber If they be heavier they sink if they be lighter they swim Now I say a mans body immediatly after he is drowned his belly being full of Water must go to the ground because in this case it will be found specifically or naturally heavier then Water That 's to say a mans body will be heavier than as much Water as is the bulk of a mans body For pleasing the fancy imagine a Statue to be composed of Water with all the true dimensions of the person that 's dead so that the one shall answer most exactly to all the dimensions of the other In this case if you counterpoise them in a Ballance the real body that 's made up of flesh blood and bones shall weigh down the other But after this dead body hath lien a short time among the Water it presently begins to swell which is caused by the fermentation of the humors of the blood which goeth before putrefaction and after three or four dayes swells so great that in effect it becomes naturally lighter than Water and therefore riseth That is to say take that body that is now swelled and as much bulk of Water as will be the precise quantity of it and having counterpoised them in a Ballance you will find the Water heavier than the body OBSERVATION IX UPon Thursday the 25 of August 1670 the following Experiment was made in a new Coal-sink on the West side of Tranent When the Coal-hewers had digged down about 6 or 7 fathom they were interrupted sometimes with ill Air therefore to know the power and force of the Damp we let down within the Bucket a Dog When he had gone down about 4 fathom or middle Sink we found little or no alteration in him save only that he opened his mouth and had some difficulty in breathing which we perceived evidently for no sooner he was pulled up to the top where the good Air was but he left off his gaping We let him down next to the bottom where he tarried a pretty while but no more change we found in him than before After this we let down a great quantity of Whins well kindled with a bold flame but they no sooner came to the middle of the sink but the flame was in an instant extinguished and no sooner was the Bucket pulled up but they took fire again This was 5 or 6 times tried with the same success If we compare this Observation with the first we will find that all Damps are not of the same power and force but that some are stronger and kills men and beasts in an instant and that others are less efficacious and more feeble and doth not so much hurt and that men may hazard to go down into a Sink where ill Air is even though fire be sometimes extinguished We see next that these Damps doth not alwayes infect the whole Air of a Coal-pit but only a certain quantity for sometimes it is found in the bottom sometimes in the middle And we see lastly that they are not alwayes of long continuance for it is found that though the Air be ill in the morning yet it may be good ere night and totally evanished ere the next day We may add as was noted in the first Observation that these Damps depend much upon the scituation of the winds seing in strong Southerly winds they are frequently in these places OBSERVATION X. OF these many excellent devices that have been found out of late the Air-pump is one first invented in Germany and afterwards much perfected in England by that Honourable Person Mr Boyl who for his pains and industry in making Experiments therewith deserves the thanks of all learned persons Several trials hath been made of late by it some whereof are as follows I took a slender Glass-tub about 40 inches long closs above and open below and filled it with VVater I next inverted it and set the orifice of it just upon the mouth of the Brass-pipe that bends upward thorow the board whereon the Receiver useth to stand and cemented them together At the first exsuction the whole VVater in the Pipe fell down and ran thorow the Brass-conduit to the Pump Having for a short while stopped the passage and thrust down the Sucker I next opened it again and the Pump being full of VVater it was driven with a considerable force up thorow the Pipe yet was it not compleatly fill'd as before by reason of some Air that I saw in the top After this was done with pleasure five or six times I opened the Stop-cock more quickly than I had used but the VVater by this means was so furiously driven up thorow the Tub that in effect it broke the end of it that was Hermetically sealed and the piece that flew off did hit the seiling so smartly that it rebounded a very far way From this we see the reason why VVater falls not down from Vessels that have narrow necks though they be inverted because it 's kept in by the force and power of the environing Air. 'T is observable that though this Pipe had been 30 foot high yet the whole VVater in it would have subsided and fallen down with one exsuction The next trial was with the help of a small Receiver which in effect was a real Cupping-glass This had a hole made in the bottom of it and was cemented to the Brass-plate and the mouth of it looking upward had a lid for covering of it I took next the lately mentioned Glass-pipe and filled it with good Brandy and having drowned the end of it among stagnant Brandy I set the Vessel wherein it was within the Receiver the Pipe coming up thorow the lid and having cemented it closly I made the first exsuction and found no descent of the Liquor from the top of the Tub. At the second it fell down about an inch At the third it fell down four or five But here appeared a great multitude of small Bubbles of Air like broken VVater near the top of the Pipe within And besides this Phenomenon there ascended from the stagnant Liquor up thorow the Pipe an infinit number of small Bubbles no bigger than Pin-heads for a very large time VVith a fourth exsuction it fell down within two or three inches of the stagnant Brandy And thinking to make the one level with the other I made a fifth but here appeared a strang effect namely
not only the whole Brandy in the Pipe subsided and was mingled with the stagnant Brandy but at this exsuction there came a great quantity of Air from the mouth of the Pipe and rose up thorow the stagnant Liquor in Bubbles Having made another exsuction there came yet more Air out and so copiously that I thought there had been some leak in the Tub through which the outward Air had entered but knowing the contrary I continued Pumping a very long time till I found less and less come out and at length after near 30 exsuctions it ceased This Air to appearance was so much as might have filled twenty Tubs every one of them as large as the Tub it came out of And surely all of it came out from among the small quantity of Brandy that filled the Pipe and that environed the mouth of it I mean the stagnant Brandy both which would not have been eight spoonful After this I opened the Stop-cock leasurely to let in the Air to the Receiver then did the Brandy climb up the Pipe slowly till it came near to the top and there made some little halt by reason of half an inch of Air that appeared there But more and more Air coming into the Receiver that half inch in the top of the Pipe did so diminish that it appeared no bigger than the point of a Pin and was scarcely discernable to the eyes What a strange and wonderful faculty of dilatation and contraction must be in the Air seing that which presently had filled the whole Tub that was 40 inches long and the sixth pâ—rt of an inch wide was contracted to as little room as the point of a Needle And by making some new exsuctions that small Atome of Air did so dilate it self again that â—t filled the same Tub and not only that but as formerly it bubbled out from the mouth of the Pipe several times 'T is to be observed that though at the first falling down of the Brandy it appeared like broken Water near the top of the Pipe within yet no such thing was seen the second time it fell down the reason is because by the first exsuctions it was well exhausted of its aërial particles Once or twice I found after the Brandy within the Pipe was well freed of Air that no exsuctions could make it move from the top of the Tub and observed a round Bubble of Air to march up which when once it came to the top did separate the one from the other If this hold good it seems to prove that neither Mercury nor any other Liquor would fall down in Pipes unless there were Air lurking amongst the parts to fill up the deserted space From this Experiment we learn that no person can well apprehend or conceive how far and to what bounds the smallest part of Air is able to expand it self And it proves evidently that when the Receiver is as much emptied as it can be by the Art of man yet it is full of Air compleatly The third trial was after this manner I set within the Receiver a little Glass half full of Brandy and the lid being cemented on I began to pump but there appeared no alteration at the first exsuction At the second I perceived a great company of very small Bubbles that for a long time ascended from the body of it and came to the surface At the third they were so frequent and great that the Brandy appeared to seeth and boil and by reason of the great ebullitions much of it ran over the lips of the Glass and fell into the bottom of the Receiver This boiling continued for the space of 7 or 8 exsuctions and by process of time the Bubbles grew fewer and fewer and when about 30 or 40 exsuctions were made no more appeared With this same sort of Brandy I filled the fore-named Pipe and set it within the Receiver the mouth of the Tub being guarded with the same sort of Liquor When it began to subside there appeared no Bubbles near the top as before the reason seems to be because the Brandy was well exhausted from its aërial particles For a fourth trial I filled the same Tub with Ale that was only 5 or 6 dayes old and drowning the end of it among stagnant Ale of the same kind I began to Pump and found that assoon as the Liquor began to subside from the top of the Pipe the whole Ale within the Pipe almost turned into Air and Froth and so many large Bubbles came up from the stagnant Liquor that I thought the whole was converted into Air. It was most pleasant to behold their several forms and shapes their order and motion This same Tub being filled with sweet milk I found very few Bubbles in it when by the exsuctions it began to subside I likewise took a little Glass-viol and fill'd the half of it full with common Ale and set it within the Receiver At the first exsuction Bubbles of Air began to rise out of it At the second and third they did so multiply that they fill'd the other half of the Glass and ran over as a Pot doth when it boileth And before I could exhaust all the Air out of it moe than 20 exsuctions passed For a fifth trial I filled the often mentioned Pipe with fountain-Fountain-water and when it began to subside by Pumping I found it leave much Air behind it But all the exsuctions I made could not make the Water of the Pipe go so low as the stagnant Water by which impediment I could Pump no Air out of the Pipe as I did while I made use of Brandy This tell us that either there is not so much Air lurking among Water as among Brandy or that the Air among this hath a more expansive faculty in it than the Air that lurks among Water If any think that it is not true and real Air which comes from the Brandy but rather the Spirits of it which evaporats I answer if a man tast this Brandy that 's exhausted of its aërial particles he will find it as strong as before which could not be if the Spirits were gone For a sixth trial I took a Frog and inclosed her within the Receiver But all the exsuctions I was able to make could not so much as trouble her Only when the Receiver was exhausted I perceived her sides to swell very big and when the Stop-cock was turned to let in the Air again her sides clapped closs together I observed likewise when the Air was pretty well Pumped out that the Frog had no respirations or if there were any they were very insensible The next day after she had been prisoner in the Receiver 24 hours I began again to Pump and after several exsuctions her sides swell'd pretty great and I perceived her open her mouth wide and somewhat like a Bag endeavouring to come out which surely hath been some of her noble parts striving to dilate themselves the body being freed of all
Pressure from the ambient Air. OBSERVATION XI TAke a slender chord about 4 or 5 yards in length and fasten the middle of it to the seiling of a Room with a nail so that the two ends of it may hang down equally Take next a piece of Wood two or three foot long two inches broad and one inch thick and boring an hole in each end of it put through the two ends of the chord and fasten them with knots but so that the piece of Wood may ly Horizontal and be in a manner a Pendulum to swing from the one end of the Chamber to the other Take next a Bullet of Lead or Iron about 20 or 24 ounces and lay it upon the said piece of Wood but because it cannot well ly without falling off therefore nail upon the ends and the sides of the Timber four pieces of Sticks on each end one and on each side one as Ledgets for keeping the Bullet from falling off All things being thus ordered draw up the piece of Wood towards the one side of the Room by which means losing its horizontal position it will ly declining-wise like the roof of an house In this position lay the Iron Bullet in the upmost end of it and then let them both pass from your fingers the one end of the Wood going foremost and you will find it swing towards the other side of the house and return again as a Pendulum This motion if the Wood be well guided in its vibrations will last perpetually because in its moving down the Bullet is hurled from the one end of the Wood to the other and hits it so smartly that it begets in it an impulse whereby it is carried farder up than it would be without it By this means the vibrations get not liberty to diminish but all of them are kept of the same length In the second vibration the same Bullet is hurled back again to the other end and hiting it with all its weight creats a second impulse wherewith the Wood is carried as far up as the point it was first demitted from Though this may seem a pretty device to please the fancy that 's many times deceived while things are presented to it by way of speculation yet upon tryal and experience there will be found an unspeakeable difficulty and it 's such an one that a man would not readily think upon I said that when the Wood was let go and was in passing down the Bullet in it would hurl down and hit the oppsite end and beget an impulse but there is no such thing for verily though the Bullet be laid upon a very declining plain Board whereupon no man could imagine a round body could ly yet all the time the Board is in swinging from the one side of the Chamber to the other and consequently sometimes under an horizontal and somtimes under an declining position the Bullet lies dead in the place where you first placed it This Observation is not so much for a perpetual motion as for finding out the reason of this pretty Phenomenon namely what 's the cause why the Bullet that cannot ly upon a reclining Board while it 's without motion shall now ly upon it while it 's under motion What is more difficult and nice to ly upon any thing that declines from a levell than Quick-silver yet lay never so much of it upon this Board while it is swinging it shall ly dead and without motion But no sooner you stop the motion of the wood but assoon the Bullet or the Quick-silver is hurled either this way or that way OBSERVATON XII I Find it mentioned by some learned persons that when a Ship is under Sail if a stone be demitted from the top of the Mast it will move down in a line parallel with it and fall at the root Some might think it ought not to fall directly above the place it hang over but rather some distance behind seing the Ship hath advanced so much bounds in the time wherein the stone is coming down Likewise while a Ship is under Sail let a man throw up a stone never so high and never so perpendicular as to his apprehension yet it will fall down directly upon his head again notwithstanding that the Ship hath run perhaps her own length in the time while the stone was ascending and descending This experiment I find to hold true which may be easily tryed especially when a man is carried in a Boat upon smooth Water drawn by a horse as is done in some places abroad Let him therefore throw up a little Stone or any heavy Body and he will find it descend just upon his head notwithstanding that the Horse that draggs the Boat be under a gallop and by this means hath advanced ten or twelve paces in the time Or while the Boat is thus running let a man throw a stone towards the brink of the VVater in this case he shall not hit the place he aimed at but some other place more forward This lets us see that when a Gun is fired in a Ship under Sail the Bullet cannot hit the place it was directed to Neither can a man riding with a full Career and shooting a Pistol hit the person he aims at but must surely miss him notwithstanding that though in the very instant of time wherein he fires the mouth of the Pistol was most justly directed For remedy whereof allowance must be granted in the aiming at the mark VVhile a man throws up a stone in a Ship under Sail it must receive two distinct impulses one from the hand whereby it is carried upward the other from the Ship whereby it is carried forward By this means the stone in going up and coming down cannot describe a perpendicular but a crooked Line either a Parabola or a Line very like unto it Neither can it describe a perpendicular Line in coming down from the top of the Mast though in appearance it seem to do so but a crooked one which in effect must be the half of that which it describes in going up and coming down For this same cause a stone thrown horizontally or towards the brink of the VVater must describe a crooked Line also And a Pistol Bullet shot while a man is riding at a full Carreer must describe a Line of the same kind Note that a man walking from the Stern of a Ship to the Head walks a longer way than in walking from the Head to the Stern Secondly a man may walk from the Head to the Stern and yet not change his place 'T is observable that a man under board will not perceive whether the Ship be sailing or not and cannot know when her Head goes about And it is strange that when a man is inclosed in a Hogs-head though he have light with him yet let him be never so oft whirled about he shall not know whether he be going about or not OBSERVATION XIII I Found in a Philosophical transaction lately Printed
that Decemb. 13. 1669 one Doctor Beal found the Mercury in the Baroscope never to be so high as it was then That same very day I found the hight of it 29 inches and nine ten parts which I never observed before And though the day here was dark and the Heavens covered with Clouds yet no rain for many dayes followed but much dryness and fair weather On Saturday night March 26 1670 I found the altitude no more than 27 and nine ten parts This night was exceeding windy with a great rain On February 1 1671. I found the altitude 30 inches and the Heavens most clear But in the most part of May following I have found the hight but 27 inches and five ten parts in which time there was abundance of rain OBSERVATION XIV NOvember 7. 1670. I made exact trial with the Magnetick Needle for knowing the variation and I found it vary from the North three degrees and a half towards the West Hevelius writes from Dantzick to the Royal Society at London Iuly 5. 1670 that it varies with him seven degrees twenty minuts west OBSERVATION XV. DEcember 17. 1669 I observed with a large Quadrant half 9 a clock at night the formost Guard-star when it was in the Meridian and lowest to have 41 degrees 22 minuts of altitude And on Ianuary 7. 1670 at 7 a clock in the morning I found it when it was in the Meridian and highest to have 70 degrees 27 minuts Hence I conclude the elevation of the Pole here to be 55 degrees 54 minuts 30 seconds and consequently as much at Edinburgh because both the places are upon one and the same Parallel OBSERVATION XVI FOr finding the true Meridian follow this method In some convenient place fix two Wyre strings with weights at them that they may hang perpendicular Then in the night time observe when the fourth star of the Plough begins to come near to the lowest part of the Meridian at which time you will find the Polar star highest Then so order the two strings by moving them hither and thither till both of them cover both the said Stars then shall they in that position give you the true South and North. This observation is the product of the seventh OBSERVATION XVII THere fell out in Mid and East-Lothian on Thursday May 11 1671 in the afternoon a considerable shour of hail with thunder and rain It came from the South-west with a great blast of wind and ran alongs from Picts-land-hills North-east towards the Sea coast The hail were big in several places as Musquet Ball and many of them rather oval than round Some persons suffered great loss of their young Pease others of their Glass Windows Eight or ten days before there was a considerable heat and dry VVeather For 20 dayes after cold Easterly winds with rain every day but especially in the end of the Moneth extraordinary rain and mist. This is so much the more to be observed because in this Countrey seldom such extraordinary hail falls out This year the Agues and Trembling Fevers have been most frequent and to many deadly OBSERVATION XVIII I Did hear lately of a curious Experiment in Germany made by a Person of note which I shall briefly in this Observation let the Reader understand And though I have heard since that it is now published in Print yet I hope it will not be impertinent to mention it here especially for their cause who cannot conveniently come to the knowledge of such things And for this reason also that I may explicat the Phenomena thereof from the foregoing doctrine and demonstrat particularly the true cause of that admirable effect that 's seen in it which I desiderat in the publisher The Auctor then takes two Vessels of Brass each one of them in form of half a sphere of a pretty large size Nothing can more fitly represent them for form and quantity than two Bee-skeps Only each of them hath a strong Ring of Brass upon the Center without and they are so contrived by the Artist that their orifices agree most exactly so that when they are united they represent an intire Sphere almost In one of the sides there 's a hole and a Brass Spigot in it through which the whole Air within is exsucted and drawn out namely by the help of the Air-pump And when by several exsuctions the Vessels are made empty the Stop-cock is turned about by which means no Air can come in And they remaining empty are taken from the Pump and do cleave so fast together that though a number of lusty fellows 12 on each side do pull vigorously by help of ropes fastned to the Rings yet are they not able to pull them asunder And because this will not do it he yokes in 12 Coach Horses six on every side yet are they not sufficient though they pull contrariwise to other to make a separation But to let the Spectators see that they may be pulled asunder he yokes in 9 or 10 on every side and then after much whipping and sweating they pull the one from the other The cause of this admirable effect is not the fear of vacuity as some do fancy for if that were all the Horses in Germany would not pull them asunder no not the strength of Angels It must then be some extrinsick weight and force that keeps them together which can be nothing else but the weight of the invironing Air. Because no sooner a force is applied that 's more powerful than the weight of the Air but assoon they come asunder And so neither six men nor six horses on each side are able to do it but nine or ten on each side makes a separation For understanding the true cause of this Phenomenon we must consider that the Vessels are 18 inches in diameter Iâ— this be then according to the last Experiment there are two Pillars of Air each one of them as heavy as a Pillar of Mercury 18 inches thick and 29 inches long by which they are united Or each Pillar of Air is as heavy as a Pillar 0â— Water 34 foot high and 18 inches in diameter For finding the weight of it in pounds and consequently the weight of each Pillar of Air by which the two Vessels are united follow this method First multiply 9 the semi-diameter of the Pillar by 54 the circumference and this gives you 486 the half whereof is the bounds of the Area namely 243. And because 34 foot contains 408 inches I multiply 408 by 243 the product whereof is 99144 so many square inches are in a Pillar of Water 34 foot high and 18 inches thick Now seing there are 1728 inches in a cubical foot I divide the number 99144 by this number and I find 57 square foot of Water and more And because every square foot weighs 56 pound Trois I multiply 56 by the number 57 and the product is 3192 pound which is the just weight of a Pillar of Water 34 foot high and 18
Mistri◠Low who had a real and true Horn growing upon the right side of her Head three inches above her righ 〈◊〉 The length of it is eleven inches and two inches about The form is crooked spirally It is convex on the outer side and somewhat guttered in the inner side It is hard and solid and all very near of the same greatness It is not hollow within as horns are ordinarily but full yet it seems to be spongious as a Cane is It was seven years in growing and was cut off in May 1671 by Mr. Temple an expert Chirurgeon here at Edinburgh OBSERVATION XXII THis Observation is for finding the Primum vivens in Animals Albeit I doubt not but the red Spirit or Blood in most Terrestrial Animals is the first product of the Primigenial juice and therefore not improperly named the true Callidum Innatum of these Creatures by the Noble and Ingenious Harvey in his Book de Generatione Neither do I scruple to yeeld that the Heart and appendent Vessels are the first formed and perfected parts in the hotter kind of Animals yet I am confident to affirm that in many of the colder and moifter kinds of Aquaticks if not in all neither the redness and heat of the Vital Spirits nor the formation of the Heart Liver c. are previously requisite to the structure and existence of the other parts seing the light of life which at first inhabited the clear and Cristalin radical moisture before the formation of any particular part doth alwayes move in every living creature according to their particular exigency without any absolute dependency upon any one part or member excepting singular conditions wherein they may be stated as to its substance light and motion there being in some Animals a simple undulation in others a slow creeping but in the more perfect an impetuous running or rather flying of the Vital Spirits necessarily required for illumination and vivification of the whole For confirmation I shall give you this singular Experiment About the middle of March the sperm of Frogs according to the number of Prolifick Eggs therein contained sends forth a multitude of small round Creatures covered with a black and moveable Frock which about the end of March and beginning of April by the Gyrations of a Tail behind like a Rudder do slowly move their bodies in the Water At this time having opened severals of them I found nothing apparent to the naked eye but a clear thin Membran under the fore-named black Frock within which were contained a clear Water and some small Fibres like Intestines and in the fore-part a small orifice like a mouth About the middle of April its motion is more vigorous and the Tripes within are most evident lying in a very fine circular order but as yet there is no Vestige of Heart Blood or Liver c. About the middle of May the feet formed like small threeds appear thorow the black Coat within the Breast the Heart is then visible of a white and Fibrous substance the Liver is white and the Gall therein easily discerned But which is the head of this Experiment the Vital Spirit in form of a clear and pure Water is manifestly received by the Nervous Heart and by the contraction thereof transmitted to all the Body thorow white transparent Vessels which being full of this Liquor do represent the Lymphatick rather than the Sanguiferous Veins Last of all do the Pneumatick Vesicles which in this Amphibium supply the place of the Lungs arise in the Breast after whose production the Lympid and Crystalin Liquor while the Heart is turgid therewith seems to be red and fiery but in the other Vessels it is of a faint pale colour untill about or near the end of Iune the Frock being cast off and a perfect Frog formed the whole Vessels are full of Blood or a red substance very thin and clear the Liver and Pneumatick Vesicles c. become red and Rosy so that the Blood in this Amphibium which in the more perfect Animals is first compleat seems to be the last part in attaining its perfection That Salmonds and great Trouts have an aqueous liquor which runs thorow their Arteries and Veins before their Blood attain the true consistency and saturat tincture I am certain whether it hold in many others I suspect but dar not affirm Hence it may be if mens observations were frequent in all kind of Anatomical inspections in several Embryo's of every species it would be found evident that the Blood in all these called 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 hath its immediat original from a simple homogeneous and uniform liquor and doth by gradual and frequent influences of the vital ferment of the heart receive at length the full tincture essence and subsistence requisite for vivification and illumination of the whole members Whether this Experiment doth not sufficiently impugn the universality of the hearts first living the original of the Gall from the fervour and ebullition of the Blood the production of the Blood by the Liver and many other ancient errors let any judge who will but take pains to make and compare Harveys trials de ov◠with this of the Porwigl or Gyrinus ab ovo Yea if the aqueous liquor be not one with the vital Spirit and subsequent Blood then my eyes and taste are altogether erroneous Moreover it were to be wished that Physitians would not simply stand upon the Galenick suppositions of the four alledged Components of the Blood nor any such or equivalent fancies of the latter Chymists but that they would seriously examine the first original and rise thereof from the Primigenial juice or liquamen the progress and perfection of its tinctures how many renovations or new tinctures it is capable of the vast difference between the Blood of old and young Animals though it may be they are both univocal substances while in their integrity within the Vessels with the specifick discriminations not only of that of any one Aquatick from any Volatil or Terrestrial but likewise of any one Species living in the same Element with these that enjoy the same Aliments but of a different Species And lastly the variety of particular constitutions and singular properties of individual Animals radicated in the fountain of life or first original of the Blood If these things and many more were truly inquired after though the Cook be sometimes necessitated to throw away some of the Broth with the Scum I doubt not but the Neoterick Invention of Transfusion of Blood would prove altogether ridiculous and the ancient mistake of too much Profusion of this treasure by Phlebotomy might suffer some reasonable checks from infallible Experience and sound reasons not here to be mentioned There are truths in Natural Philosophy which I doubt not but sound reason and experience will convince the vain world of in due time OBSERVATION XXIII THis Observation is concerning the aliment and growth of Plants The inquisitive wits of this and the last