Experimental investigation of the spirit manifestations, [electronic ...

376 OF MATTER, MIND, AND SriRIT.called for. It lias, for some years, occurred to nic, that the Newtoniandoctrine of radiation might be associated with that of undulation.1830. The fact that radiant heat could be collected by a mirror so as toraise the temperature of bodies placed in the focus, and that this processcould take place in vacuo, as ascertained by Sir Humphrey Davy, had beenadduced as unquestionable evidence of the materiality of caloric,the supposedfluid cause of heat. But as the cold proceeding from a snowball orany cold body could be collected by the same process, it was urged bysome chemists that the evidence of the materiality of the cause of coldmust also be admitted.Prevost met this argument by suggesting that nobody in nature is absolutely cold. Every body, however refrigerated, isnot so cold as to be incapable of greater refrigeration. Hence all bodiesbeing absolutely above the zero of nature, are throwing off rays to eachother, and where there is equality of temperature, they do not cause anychange in their relative temperatures. The rays thrown off by A are compensatedby those which it receives from B, and vice versa. But if Athrows off to B more than B reciprocates, the temperature of A must falluntil an equilibrium is attained. Thus, A being the mirror and B thesnowball, the mirror is refrigerated, and causes a greater radiation fromany body situated about its focus. This explanation was generally received,but to me, the following rationale, which I advanced, appearedpreferable :1831. I assumed caloric to exist throughout the sublunary creation, asthe luminiferous ether is assumed to be diffused throughout all space bythe undulationists ; the diffusion arising from the reciprocal repulsion ofits particles being similar to that which had been supposed to cause thediffusion of caloric. There is the greatest analogy between this diffusionand that which is known to exist in the case of gases. The process is thesame, whether the gas be dense like chlorine, or thirty-six times as rare,as in the instance of hydrogen, and in the luminiferous ether resemblesthe process by which hydrogen is rarilied, or might be rendered more rare,were the pressure of the atmosphere removed.1832. It is known that in any gas or gaseous mixture like that which webreathe, if a deficit of pressure be caused in any spot, the gaseous particleswill quickly move toward it, in order to restore the equilibrium ofpressure, and that if, on the other hand, any augmentation of pressure beproduced at any spot, the gas will move outward to restore the equilibrium.1833. The particles being symmetrically arranged in lines, a row ofparticles may be conceived to lie between every two remote points. If wesuppose any number of points in the focal body, and a correspondingnumber in the surface of the mirror, it may be conceived that the interveningethereal or calorific particles will move in rows one way or the other,as the pressure in the focal space may become greater or less. Thus aneffect is brought about, equivalent to that which the Newtonian idea of