ABSTRACT
Line 34 Sir Isaac Newton at the end of the last edition of his Optics, supposes that a very subtile and elastic fluid, which he calls aether, is diffused thro’ the pores of gross bodies, as well as thro’ the open spaces that are void of gross matter; he supposes it to pierce all bodies, and to touch their least particles, acting on them with a force proportional to their number or to the matter of the body on which it acts. He supposes likewise, that it is rarer in the pores of bodies than in open spaces, and even rarer in small pores and dense bodies, than in large pores and rare bodies; and also that its density increases in receding from gross matter; so for instance as to be greater at the of an inch from the surface of any body, than at its surface; and so on. To the action of this aether he ascribes the attractions of gravitation and cohaesion, the attraction and repulsion of electrical bodies, the mutual influences of bodies and light upon each other, the effects and communication of heat, and the performance of animal sensation and motion. David Hartley from whom this account of aether is chiefly borrowed, makes it the instrument of propagating those vibrations or configurative motions which are ideas. It appears to me, no hypothesis ever involved so many contradictions; for how can the same fluid be both dense and rare in the same body at one time? yet in the Earth as gravitating to the Moon, it must be very rare; and in the Earth as gravitating to the Sun, it must be very dense. For, as Andrew Baxter well observes, it doth not appear sufficient to account how this fluid may act with a force proportional to the body to which another is impelled, to assert that it is rarer in great bodies than in small ones: it must be farther asserted that this fluid is rarer or denser in the same body, whether small or great, according as the body to which that is impelled is itself small or great. But whatever may be the solidity of this objection, the following seems unanswerable:
If every particle thro’ the whole solidity of a heavy body receive its impulse from the particles of this fluid, it should seem that the fluid itself must be as dense as the very densest heavy body, gold for instance; there being as many impinging particles in the one, as there are gravitating particles in the other which receive their gravitation by being impinged upon: so that, throwing gold or any heavy body upward, against the impulse of this fluid, would be like throwing gold thro’ gold; and as this aether must be equally diffused over the whole sphere of its activity, it must be as dense when it impels cork as when it impels gold: so that to throw a piece of cork upward, would be as if we endeavoured to make
cork penetrate a medium as dense as gold: and tho’ we were to adopt the extravagant opinions which have been advanced concerning the progression of pores, yet however porous we suppose a body, if it be not all pore, the argument holds equally; the fluid must be as dense as the body in order to give every particle its impulse.
