motion, which, in theory, is absolutely a perpetual one. Whence it appears, fourthly, that the fieri nequit, to which Mr. Cotes hath reduced himself, hath affirmed too much, and confuted itself. For if the preffure of the surrounding fluid be greater on the illuminated side of the vanes, than its resistance on the opposite sides; that inequality of pressure will necessarily produce a motion toward the weaker side; and for the same reason that it produces, it would also conserve the motion for ever. Fifthly and lastly, the well-known inference from a continuance of motion is worst of all: for, if the machine were placed in a vacuum, that is, in a space void of air, the lights would expire, and motion be at an end. A small hint will be sufficient here by way of application; only let it be remembered, that the lights we use for experiment-sake, will decay in spite of us; whereas that lamp, which God hath lighted up in the world, never goes out. And he that can retain so mean an opinion of the sun, that marvellous instrument of the divine wisdom, as to suppose it acts, not by the emanation of its light, but by its quantity of solid matter, should. put out the two lamps and weigh them, in order to ac

count for this experiment. If this is not enough to convince the ingenious part of our mathematicians, that their science hath been misapplied, and that their way of reasoning upon physical causes is fundamentally wrong, they must be left to philosophize suo more if they are deaf to the evidence of nature, it is hardly to be expected they will yield to any remonstrances of mine.

low me.

As the doctrine of a vacuum, and the theory of resistances, are points of so much. importance, I have tried to be as particular as the cause required, and as methodical and perspicuous as my small abilities would alIf there be a considerable defect in any of my deductions, I shall be very glad to be better informed; and perhaps some of the followers of Sir Isaac Newton may shew so much candour and humility toward a man who means well, as not to think him too insignificant to be taken notice of.

CHAP.

CHAP. VI.

A Geometrical Argument for a Vacuum examined and refuted.

EXP

XPERIMENT and logic having both failed in the demonstration of a vacuum; let us see what stress is to be laid on geometry in the case before us for we have been so stunned of late years with its praises, that it will be neither prudent nor handsome to overlook its pretensions. Dr. Keil, the astronomical professor, was a very a very eminent geometrician, and as strenuous an advocate in behalf of a vacuum. To convince us that there really is such a thing in nature, he offers the following demonstration, which I fix upon, because it has the author's own commendation, who calls it an invincible one, as the reader will find in the 17th page of his Philosophical Lectures. He desires us to

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suppose all the matter in the universe to "be amassed into two spheres, which may "be represented by two circles, whose

centers are A and B. If these spheres "touch one another, it is necessary that

they touch one another in one point only by the elements of geometry-and there"fore there will be betwixt the other points "of these spheres a certain and determinate space not replete with matter.' Hence the author concludes "that there is in "reality a space distinct from all body. P. 19.

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This is Dr. Keil's invincible demonstration for the erecting of which, you are only to allow this small supposition, that the omnipotence of God might possibly accumulate all the matter of the universe into two solid spheres; and because there would be in this case a space void of all matter, it follows, in his way of reasoning, that there really is such a space. This author seems to have been so full of geometry, that there was no room for any logic; else he might have picked up enough of it at Oxford to have taught him-a posse ad esse non valet consequentia. Besides, it is the proper business of a philosopher to consider the operations of nature, as nature is now constructed; where, I apprehend, he will find work enough without making a new world, or shuffling the old one into a new shape. But Dr. Keil imagined it would edify us

more,

more, to tell us what strange things would happen, if the world were all taken to pieces, and put together again in such a form as could answer no one purpose of the creation.

If a question had been put to him, whether the motion of a pendulum in a clock is preserved by the action of occult virtues, propagated through void spaces from one wheel to another, or by a contact and bearing of the parts upon one another from the weight to the pendulum; he might have demonstrated the former invincibly, by supposing, that if the matter of the whole machine were melted down, and made up again into a couple of wheels, their circumferences could touch one another but in a single point; and a man might make a clock upon this principle, with just as much accuracy as he can philosophize upon the other. He that will impartially consider this, and many other geometrical arguments of the same

plexion, (with which I could fill a book if it were necessary,) will not be very hasty to believe any proposition, because it is said to be supported by mathematical evidence; which, though it be strong in its proper place, and undeniable if considered in the abstract, is nevertheless, when misapplied,

just