Sir Ifaac Newton, Though it may be questioned, whether what is thought a change be not only a disguise.

149. Fire feems the most elastic and expansive of all bodies. It communicates this quality to moitt vapours and dry exhalations, when it heats and agitates their parts, cohering closely with them, Overcoming their former mutual attraction, and causing them, instead thereof, reciprocally to repel each other and fly afunder, with a force proportionable to that wherewith they had cohered.

150. Therefore in air we may conceive two parts, the one more grofs which was raised and carried off from the bodies of this terraqueous mass: the other a fine fubtile fpirit by means whereof the former is rendered volatile and elastic. Together they compofe a medium, whofe elasticity. is less than that of pure æther, fire, or fpirit, in proportion to the quantity of falts, vapours, and heterogeneous particles contained therein. Hence it follows, that there is no fuch thing as a pure fimple element of air. It follows alfo, that on the higheft mountains air fhould be more rare than in proportion to the vulgar rule, of the spaces being reciprocally as the preffures: and fo in fact it is faid to have been found, by the gentlemen of the French Academy of Sciences.

151. Æther, fire, or fpirit being attracted and clogged by heterogeneous particles becometh lefs active; and the particles cohering with those of æther, become more active than before. Air therefore is a mass of various particles, abraded and sublimated from wet and dry bodies of all forts, cohering with particles of æther; the whole permeated by pure æther, or light, or fire: for these words are used promifcuously by ancient philofophers.

152. This

152. This æther or pure invifible fire, the moft fubtile and elaftic of all bodies, feems to pervade and expand it felf throughout the whole univerfe. If air be the immediate agent or inftrument in natural things, it is the pure invifible fire that is the firft natural mover or fpring, from whence the air derives it's power (a). This migh ty agent is every where at hand, ready to break forth into action, if not reftrained and governed with the greatest wisdom. Being always reftlefs and in motion, it actuates and enlivens the whole vifible mafs, is equally fitted to produce and to deftroy, diftinguishes the various stages of nature, and keeps up the perpetual round of generations and corruptions, pregnant with forms which it conftantly fends forth and reforbs. So quick in it's motions, fo fubtile and penetrating in it's nature, fo extenfive in it's effects, it feemeth no o ther than the vegetative foul or vital spirit of the world.

153. The animal fpirit in man is the inftrumental or phyfical caufe both of fenfe and ma tion. To fuppofe fenfe in the world, would be grofs and unwarranted. But loco-motive faculties are evident in all it's parts. The Pythagoræans, Platonifts, and Stoics held the world to be an animal. Though fome of them have chofen to confider it as a vegetable, However the phænomena and effects do plainly fhew there is a spirit that moves, and a mind or providence that prefides. This providence, Plutarch faith, was thought to be in regard to the world, what the foul is in regard to man.

154. The order and courfe of things, and the experiments we daily make, fhew there is a mind that governs and actuates this mundane fyftem, (a) 139, 149, 151,

as

as the proper real agent and caufe. And that the inferior inftrumental caufe is pure æther, fire, or the fubftance of light (c) which is applied and determined by an infinite mind in the macrocofm or univerfe, with unlimited power, and according to ftated rules; as it is in the microcofm, with limited power and fkill by the human mind. We have no proof either from experiment or reason, of any other agent or efficient cause than mind or fpirit. When therefore we speak of corporeal agents or corporeal caufes, this is to be undertood in a different, fubordinate, and improper fenfe.

155. The principles whereof a thing is compounded, the inftrument ufed in its production, and the end for which it was intended, are all in vulgar ufe termed Causes, though none of them be ftrictly speaking agent or efficient. There is not any proof that an extended corporeal or mechanical caufe doth really and properly act, even motion itself being in truth a paffion. Therefore though we speak of this fiery fubftance as acting, yet it is to be understood only as a mean or inftrument, which indeed is the cafe of all mechanical caufes whatfoever. They are nevertheless fometimes termed agents and caufes, although they are by no means active in a strict and proper fignification. When, therefore, force, power, virtue, or action are mentioned as fubfifting in an extended and corporeal or mechanical being, this is not to be taken in a true, genuine, and real, but only in a grofs and popular fenfe, which sticks in appearances, and doth not analyse things to their first principles. In compliance with eftablished language, and the ufe of the world, we muft employ the popular current phrafe. But then in regard to truth we ought to diftinguish

(c) 29, 37, 136, 149.

its meaning. It may fuffice to have made this declaration once for all, in order to avoid miftakes.

156. The calidum innatum, the vital flame, or animal fpirit in man is fuppofed the cause of all motions, in the feveral parts of his body, whether voluntary or natural. That is, it is the inftrument, by means whereof the mind exerts and manifefts herself in the motions of the body. In the fame fenfe may not fire be faid to have force, to operate, and agitate the whole fyftem of the world, which is held together and informed by one prefiding mind, and animated throughout by one and the fame fiery substance, as an inftrumental and mechanical agent, not as a primary real efficient?

157. This pure fpirit or invifible fire is ever ready to exert and fhew itself in its effects (d), cherishing, heating, fermenting, diffolving, fhi ning and operating in various manners, where a fubject offers to employ or determine its force. It is prefent in all parts of the earth and firmament, though perhaps latent and unobferved, till fome accident produceth it into act, and renders it vifible in its effects.

158. There is no effect in nature, great, marvellous, or terrible but proceeds from fire, that diffufed and active principle, which at the fame time that it shakes the earth and heavens, will enter, divide, and diffolve the fmalleft, clofeft, and most compacted bodies. In remote cavities of the earth it remains quiet, till perhaps an accidental fpark from the collifion of one ftone against another kindles an exhalation, that gives birth to an earthquake or tempeft, which fplits mountains, or overturns cities. This fame fire ftands unfeen in (d) 152.

the

the focus of a burning glafs, till fubjects for it to act upon it come in it's way, when it is found to melt, calcine, or vitrify the hardest bodies.

159. No eye could ever hitherto difcern, and no fenfe perceive, the animal fpirit in a human body, otherwife than from it's effects. The fame may be faid of pure fire, or the fpirit of the univerfe, which is perceived only by means of fome other bodies, on which it operates, or with which it is joined. What the chemists fay, of pure acids being never found alone, might as well be faid of pure fire.

160. The mind of man acts by an inftrument neceffarily. The to yeμovinov, or mind prefiding in the world, acts by an inftrument freely. Without inftrumental and fecond caufes, there could be no regular courfe of nature. And without a regular courfe, nature could never be understood. Mankind must always be at a lofs, not knowing what to expect, or how to govern themselves, or direct their actions for the obtaining of any end. Therefore in the government of the world phyfical agents, improperly fo called, or mechanical, or fecond caufes, or natural caufes, or inftruments,' are neceffary to affift, not the governor, but the governed.

161. In the human body the mind orders and moves the limbs: but the animal fpirit is fupposed the immediate phyfical caufe of their motion. So likewife in the mundane fyftem, a mind prefides, but the immediate, mechanical, or inftrumental caufe, that moves or animates all it's parts, is the pure elementary fire or fpirit of the world. The more fine and fubtile part or fpirit is fuppofed to receive the impreffions of the firft mover, and communicate them to the groffer fenfible parts of this world. Motion, though in metaphyfical

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