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and constant would cease to be rules. There is therefore a constancy in things, which is styled the course of nature (a). All the phænomena in nature are produced by motion. There appears an uniform working in things great and small, by attracting and repelling forces. But the particular laws of attraction and repulsion are various. Nor are we concerned at all about the forces, neither can we know or measure them otherwise than by their efsects, that is to fay, the motions, which motions only, and hot the forces, are indeed in the bodies (£). Bodies are moved to or from each other, and this is performed according to different laws. The natural or mechanic philosopher endeavours to discover those laws by experiment and reasoning. But what is faid of forces residing in bodies whether attracting or repelling, is to be regarded only as a mathematical hypothesis, and not as any thing really existing in nature.
235. We are not therefore seriously to suppose with certain mechanic philosophers, that the minute particles of bodies have real forces or powers by which they act on each other, to produce the various phænomena in nature. The minute corpuscles are impelled and directed, that is to fay, moved to and from each other according to various rules or laws of motion. The laws of gravity, magnetism, and electricity are divers. And it is not known, what other difserent rules or laws of motion might be established, by the author of nature. Some bodies approach together, others fly asunder, and perhaps some others do neither. When fait of tartar flows per deliquium, it is visible that she particles of water floating in the air
- * (a) 160. (i) 155.
are are moved towards the particles of fait, and joined with them. And when we behold vulgar salt not to. flow per deliquium, may we not conclude that the fame law of nature and motion doth not obtain between it's particles and those of the floating vapours? A drop of water assumes a round figure, because it's parts are moved towards each other. But the particles of oil and vinegar have no such disposition to unite. And when flies walk in water without wetting their seet, it is attributed to a repelling force or faculty in the fly's seet. But this is obscure, though the phænomenon be plain.
236. It is not improbable, and seems not unsupported by experiments, that, as in algebra, where positive quantities cease there negative begin, even so in mechanics, where attracting forces cease there repelling forces begin; or (to express it more properly) where bodies cease to be moved towards, they begin to be moved from each other. This sir Ifaac Newton insers from the production of air and vapours, whose particles fly asunder with such vehement force. We behold iron move towards the loadstone, straws towards amber, heavy bodies -towards the earth. The laws of these motions are -various. And when it is faid, that all the motions and changes in the great world arise from attraction; the elasticity of the air, the motion of water, the descent of heavy, and the ascent of light bodies, being all ascribed to the fame principle; when from insensible attractions of most minute particles at "the smallest distance, are derived cohesion, dissolution, coagulation, animal secretion, sermentation, and all chemical operations; and when it is faid, that without such principles there never would have been any motion in the world, and without - i the the continuance thereof all motion would cease, In all this we know or understand no more, than that bodies are moved according to a certain order, and that they do not move themselves.
237. So likewise, how to explain all those various motions and efsects, by the density and elasticity of aether, seems incomprehensible (a). For instance, why should the acid particles draw those -of water and repel each other? why should some salts attract vapours in the air, and others not? why should the particles of common falt repell each.other, so as not to subside in water? why should the most repellent particles be the most attractive upon contract? Or why should the repellent begin where the attractive faculty leaves off. These, and numberless other effects seem inexplicable on mechanical principles, or otherwise than by recourse to a mind or spiritual agent (i). Nor will it suffice from present phænomena and effects, through a chain of natural causes, and subordinate blind agents, to trace a divine intellect as the remote original cause, that first created the world, and then set it a going. We cannot make even one single step in accounting for the phænomena, without admitting the immediate presence and immediate action of an incorporeal agent, who connects, moves, and disposes all things, according to such rules, and for such purposes as seem good to him.
238. It is an old opinion adopted by the moderns, that the elements and other natural bodies art changed each into other (c). JNbw, as the particles of different bodies are agitated by different forces, attracting and repelling, or, to speak more accurately, are moved by different laws, how can these forces
(«)'153,162. -si) 154,2-20. ;(*) i+i.
or laws be changed, and this change accounted fof by an elastic æther? Such a medium, distinct from light or fire, scemeth not to be made out by any proof, nor to be of any use in explaining the phænomena. But is there be any medium employed, as a subordinate cause or instrument -in attraction, it would rather seem to be light (k); since by an experiment of Mr. Boyle's, amber, thac stiewed no sign of attraction in the shade, being placed where the sun-beams shone upon it, immediately attracted light bodies. Besides, it hath been discovered by sir Ifaac Newton4 and an admirable discovery it was, that light is an heterogeneous medium (I) confisting of particles endued with original distinct properties. And upon these, if I may. venture to give my conjectures, it scemeth probable the specisic properties of bodies, and the force of specific medicines may depend. Disserent sides of the fame ray shall, one approach and the other recede from the Iflandic crystal; can this be accounted for by the elasticity of a fine medium, or by the general laws of motion, or by any mechanical principles whatever? And is not, what should hinder but there may be specific medicines, whose operation depends not upon mechanical principles, how much soever that notion hath been exploded of late years?
239. Why may we not suppose certain idiosyncrasies, sympathies, oppositions, in the solids or fluids or animal spirit of a human body, with regard to the fine insensible parts of minerals or vegetables, impregnated by rays of light of disserent properties, not depending on the disserent size,. figure, number, solidity or weight of those particles,
nor on the general laws of motion, nor on the density or elasticity of a medium, but merely and altogether on the good pleasure of the Creator, in the original formation of things? From whence divers unaccountable and unforeseen motions may arise in the animal ceconomy; from whence also various peculiar and specific virtues may be conceived to arise, residing in certain medicines, and not to be explained by mechanical principles. For although the general known laws of motion are to be deemed mechanical, yet peculiar motions of the insensible parts, and peculiar properties depending thereon, are occult and specific.
240. The words attraction and repulsion may, in compliance with custom, be used where, accurately speaking, motion alone is meant. And in that sense it may be faid, that peculiar attractions or repulsions in the parts, are attended with specific properties in the wholes. The particles of light are vehemently moved to or from, retained or rejected by objects. Which is the fame thing as to fay with fir Ifaac Newton, that the particles of acids are endued with great attractive force wherein their activity consists; whence sermentation and dissolution ; and that the most repellent are, upon contact, the most attracting particles.
241. Gravity and sermentation are received foe two most extensive principles. From sermentation are derived the motion and warmth of the heart and blood in animals, subterraneous heat, fires, and earthquakes, meteors and changes in the atmosphere. And, that attracting and repelling forces operate in the nutrition arrdaissolution of animal and vegetable bodies, is the doctrine both of Hip