STATICS. ΑΝ Hydroftatical Difcourfe, By way of Anfwer to the Objections of Dr. MORE, and others, against fome Explanations of particular Experi ments: With farther Confiderations thereon. F SECT. I. Inding no cause to alter my judgment, as to the folutions I have Mechanical given, of fome of my experiments, attack'd by Dr. More; Ifolutions of here defign to vindicate them from his objections. gra And, firft, the Doctor having made a defcription of my pneumatic engine, pretends, that the afcent of the fucker, after it is deprefs'd, and clogg'd with a weight, is not mechanically accounted for, by the vity and preffure of the atmosphere; because, says he, "if this folution "were truly mechanical, he must have affign'd the true mechanical cause "of the gravity of all the parts, and of the whole atmosphere." To this I anfwer, that in delivering my experiments about the effects of the air, I did not intend to write a whole fyftem, or fo much as the elements of natural philofophy; but having fufficiently prov'd, that the air we live in, is not deftitute of weight, and has an elaftic power; I endeavour'd, by those two principles, to explain the phenomena exhibited in our engine; without recourse to a Fuga vacui, an Anima mundi, or any fuch unphilofophical principle. And fince fuch kinds of explanations have, of late, generally been call'd, mechanical, as being grounded upon the laws of mechanics, I thought, as I permit, so I might be allow'd, the use of that term; and to entitle my explanations, mechanical, in the usual sense of that expreffion. I am not obliged to treat of the cause of gravity in general, fince many propofitions of Archimedes, Stevinus, and others, who have Yy 2 written phenomena, what? STATICS. Written of ftatics, are confefs'd to be mathematically, or mechanically demonftrated; tho' thofe authors do not affign the true caufe of gravity, but take it for granted, as a thing univerfally acknowledg'd. And, if in each fcale, of an ordinary balance, a pound weight, for inftance, be put; he who fhall fay, that the fcales hang in equilibrium, because the equal weights balance one another; and, in cafe an ounce be added to one of the fcales, and not to the oppofite, he who fhall fay, that the former is deprefs'd, becaufe urg'd by a greater weight than the other, will be thought to have given a mechanical explanation of the equilibrium of the fcales, and their lofing it; tho' he cannot give a true caufe why either of those fcales tends towards the center of the earth. Since, then, to affign the true cause of gravity, is not required, even in ftatics, tho' one of the principal, and most known parts of mechanics; why may not other propofitions, and accounts, that fuppofe gravity in the air, and prove it too, be look'd on as mecha nical? The Doctor, however, is pleas'd to grant me almost as much as I need defire, as to the truth of the hypothefis whereon my explanations are founded. The principal thing which I fuppofe, in my hydroftatical writings is, that in water, tho' ftagnant, the upper parts actually gravitate upon the lower; or prefs upon them, even when they do not fenfibly deprefs them. This hypothefis, the Doctor allows, agreeable to the principles of the mechanical philofophy: and, accordingly, having fhew'd, that in a fufpended tube of water, the whole liquor gravitates upon the bottom of it; and, confequently, that all the parts thereof do fo, the upper upon the lower, "provided" fays he" "there be no immaterial principle in nature.” Now, I as freely, as the Doctor himself, affert an incorporeal Being, that made and governs the world. All that I have endeavour'd at, in explaining what happens among inanimate bodies, is to fhew, that fuppofing the world to have been at firft made, and to be continually preferv'd by God's divine power and wifdom; and fuppofing his general concourfe to the maintenance of the laws he has establish'd in it; the phenomena I confider, may be folv'd mechanically; that is, by the mechanical properties of matter; without recourse to nature's abhorrence of a vacuum, to fubftantial forms, or to other incorporeal creatures. And, therefore, if I have shewn, that the phenomena, I attempted to folve, are explicable by the motion, magnitude, gravity, fhape, and other mechanical affections of the small parts of liquors; I have done what I pretended: which was not to prove, that no angel, or other immaterial creature, could interpofe in these cases; for, concerning fuch agents, all that I need fay, is, that, in the cafes proposed, we want not their affiftance; and, therefore, have no occafion to fly to it, in folving our phenomena. That the upper But the Doctor, it seems, would have the gravitation of the elements, in their parts of fluids proper places, fufpended by an incorporeal principle; and hereto he is led gravitate upon by this experiment, which, he fays, is moft manifeftly repugnant to our hypothefis. He conceives, then, that in a bucket of water, with a perfectly cylindrical cavity, whofe diameter is of 62 parts, there is forcibly the lower. kept at the bottom, by means of a ftick, a round piece of wood, whofe STATICS. diameter amounts but to 61 of thofe parts; and that as foon as ever the stick is remov'd, the piece of wood will emerge to the top, and float: "which," fays he is impoffible, if all the parts of the water, did not only jointly prefs the bottom of the veffel, but each prefs'd the other di"rectly downwards." 66 But, first, fince according to his computation, the area of the interval between the fides of the veffel, and the edges of the round board, is 123 of fuch parts, whereof the area of the board amounts to 37213 'tis evident, that there must be room enough for the water to pafs between the fides of the veffel, and the edges of the board; which is fuppofed, on all hands, to be of fome wood lighter in fpecie than water, fince elfe it would not rife, upon with-drawing the ftick. Secondly, this round board is not fuppos'd to be made exactly fit to the bottom of the veffel, and, confequently, the water may get in between them; for which reason, 'tis neceffary to keep the piece of wood forcibly down with a stick; which were otherwife needlefs; and, confequently, this interpos'd water, will communicate with the upper, along the fides of the veffel; which latter may, according to the laws of hydroftatics, by means of that interpofed, exercise its preffure upwards, against the lower furface of the wooden plate. Thirdly, the Doctor fuppofes an imaginary plane of water to be parallel to the bottom of the veffel, and to pass along the bottom of the board; so that of the water that lies between this plane, and the bottom of the veffel, one part is cover'd by the piece of wood; and the other, between the edges of that, and the fides of the bucket, is cover'd with the incumbent water only. Now, 'tis manifeft, that in water, thofe parts which are most prefs'd, will thruft out of their place, thofe that are lefs prefs'd. 'Tis alfo evident, that the part of the imaginary plane, cover'd by the round piece of wood, must be prefs'd by a lefs weight than the other part of the fame plane; because the wood being, bulk for bulk, lighter than water, the aggregate of the wood and water, incumbent on the cover'd part of the fame plane; muft be lighter in fpecie, than the water alone, that is incumbent on the uncover'd part of the fame plane; and, confequently, this uncover'd part being more prefs'd than the other part of the plane, the heavier must displace the lighter; which it cannot do, but by thrufting up the board; as it does when the external force that kept it down, is removed. And this greater preffure against the bottom, than against the top of bodies immers'd in water, fpecifically heavier than themselves, is a true reafon of their emerfion. 'Tis true, that according to the Doctor's computation, if the folid cylinder, consisting of the wooden plate, and all the water directly incumbent on it, were put into an ordinary balance; it would there greatly outweigh the hollow cylinder of water alone, that refts upon the uncover'd part of the imaginary plane. And this is what feems to have deceiv'd the 2 Doctor: |