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gravity, is not explained by elasticity, a phænomenon not less obscure than itself. But then, although it shews not the agent, yet it sheweth a rule and an alogy in nature to say, That the folid parts of animals are endued with attractive powers, whereby from contiguous fluids they draw like to like; and that glands have peculiar powers attractive of peculiar juices (6). Nature seems better known and explained by attractions and repulsions, than by those other mechanical principles of lize, figure, and the like: that is, by Sir Isaac Newton, than Descartes. And natural philosophers excel, as they are more or less acquainted with the laws and methods observed by the Author of nature.
244. The size and shape of particles, and general laws of motion can never explain the secretions without the help of attraction, obscure perhaps as to its cause, but clear as a law. Numberlefs instances of this might be given : Lemery the younger thought himself obliged to suppose, the particles of light or fire (contrary to all reason) to be of a very gross kind, even greater than the pores of the burnt limestone, in order to account for their being detained or imprisoned therein ; but this phænomenon is easily reduced to attraction. There would be no end of enumerating the like cases, The activity and force of ætherial spirit or fire by the laws of attraction is imparted to grosser particles (P), and thereby wonderfully supports the economy of living bodies. By such peculiar compositions and attractions it seems to be effected, that denfer fluids can pass where air itself cannot (45 oil through leather) and therefore through
W 152, 163,
the nicest and finest strainers of an animal or vegetable.
245. The ancients had some general conception of attracting and repelling powers (9) as natural principles. Galilæi had particularly considered the attraction of gravity, and made fome discovery of the laws thereof. But Sir Isaac Newton by his fingular penetration, profound knowledge in geometry and mechanics, and great exactness in experiments, hach cast a new light on natural science. The laws of attraction and repulsion were in many instances discovered, and first discovered, by him. He shewed their general extent, and therewith, as with a key, opened several deep secrets of nature, in the knowledge whereof he seems to have made a greater progress, than all the fects of corpusculariar together had done before him. Nevertheless, the principle of attraction itself is not to be explained by physical or corporeal causes.
246. The Cartesians attempted to explain it by the nisus of a subtil element, receding from the center of its motion, and impelling groffer bodies towards it. Sir Isaac Newton in his later thoughts seems (as was before observed) to have adopted somewhat not altogether foreign from this notion, afcribing that to his elastic medium (r) which Dercartes did to his second element. But the great men of antiquity resolved gravity into the immediate action of an intelligent incorporeal being. To which also Sir Isaac Newton himself attests and subscribes, although he may perhaps sometimes be thought to forget himself, in his manner of speaking of physical agents, which in a strict sense are none at all, and in fupposing real forces to exist in bodies, in
(9) 241, 242.
(1) 237, 238.
which, to speak truly, attraction and repulsion should be considered only as tendencies or motions, that is, as mere effects, and their laws as laws of motion.
247. Though it be supposed the chief business of a natural philosopher to trace out causes from the effects, yet this is to be understood not of agents (s) but of principles, that is, of component parts, in one sense, or of laws or rules, in another. In strict truth all agents are incorporeal, and as such are not properly of physical consideration. The Astronomer, therefore, the Mechanic, or the Chemist, not as such, but by accident only, treat of real causes, agents or efficients. Neither doth it seem, as is supposed by the greatest of mechanical philosophers, that the true way of proceeding in their science is, from known motions in nature to investigate the moving forces. Forasmuch as force is neither corporeal, nor belongs to any corporeal thing (t); nor yet to be discovered by experiments or mathematical reasonings, which reach no farther than discernible effects, and motions in things passive and moved.
248. Vis or force is to the soul, what extension is to the body, faith faint Auguftin, in his tract concerning the quantity of the Soul; and without force there is nothing done or made, and consequently there can be no agent Authority is not to decide in this case. Let any one confult his own notions and reason, as well as experience, concerning the origin of motion, and the respective natures, properties, and differences of soul and body, and he will, if I mistake not, evidently perceive, that there is nothing active in the latter. Nor are they natural
agents or corporeal forces, which make the particles of bodies to cohere. Nor is it the business of experimental philosophers to find them out.
249. The mechanical philosopher, as hath been already observed, inquires properly concerning the rules and modes of operation alone, and not concerning the cause, forasmuch as nothing mechanical is or really can be a cause (u). And although a mechanical or mathematical philosopher may speak of absolute fpace, absolute motion, and of force as existing in bodies, causing such motion and proportional thereto; yet what these forces are, which are supposed to be lodged in bodies, to be impressed on bodies, to be multiplied, divided, and communicated from one body to another, and which seem to animate bodies like abstract spirits or souls, hath been found very difficult, not to say impossible, for thinking men to conceive and explain ; as may be seen by consulting Borellus De vi percussionis, and Torricelli in his Lezioni academiche, among other authors.
250. Nor, if we consider the proclivity of mankind to realize their notions, will it seem strange that mechanic philosophers and geometricians should, like other men, be misled by prejudice, and take mathematical hypotheses for real beings existing in bodies, fo far as even to make it the very aim and end of their science to compute or measure those phantoms; whereas it is very certain that nothing in truth can be measured * or computed, beside the very effects or motions themselves. Sir Isaac Newton asks, Have not the minute particles of bodies certain forces or powers by which they act on
(u) 236, 247 * This subject is handled at large in my Latin tract De motu, published above twenty years ago.
one another, as well as on the particles of light, for producing most of the phænomema in nature? But in reality, those minute particles are only agitated according to certain laws of nature, by some other agent, wherein the force exists and not in them, which have only the motion, which motion in the body moved, the Peripatetics rightly judge to be a mere passion, but in the mover to be évégzerce
251. It passeth with many, I know not how, that mechanical principles give a clear solution of the phænomena. The Democritic hypothesis, faith doctor Cudworth, doth much more handsomely and intelligibly solve the phænomena, than that of Aristotle and Plato. But things rightly considered, perhaps it will be found not to solve any phænomenon at all. For all.phænomena are, to speak truly, appearances in the soul or mind; and it hath never been explained, nor can it be explained, how external bodies, figures, and motions should produce an appearance in the mind. Those principles, therefore, do not solve, if by solving is meant asigning, the real, either efficient or final, cause of appearances, but only reduce them to general rules.
252. There is a certain analogy, constancy, and uniformity in the phænomena or appearances of nature, which are a foundation for general rules: and these are a grammar for the understanding of nature, or that series of effects in the visible world, whereby we are enabled to foresee what will come to pass, in the natural course of things. Plotinus obferves, in his third Ennead, that the art of
presaging is in some sort the reading of natural letters denoting order, and that so far forth as analogy obtains in the universe, there may be vaticination. And in reality, he that foretells the motions of the