Newton, quite singularly, while rejecting the wave-theory of light, gave his assent to the analogous ideas respecting heat; and, in so far as we may judge, conceived the warmth excited in a body when exposed to light or radiant heat to be due to the little shocks which luminous or radiant material might produce in it.
Huyghens, Hooke, Locke, and Cavendish, among others, were also favorably inclined to the Baconian view; the works of Hooke particularly containing many and strong expositions of the vibratory notion, and his comments on the mechanical and chemical production of heat being urged often with as great clearness, and as subtile a perception of occult natural causes, as any which we now possess.
But the adaptation of the known "laws of motion" to these operations, whereby heat might in many instances have been directly correlated to the energy expended in producing it, was not until long after definitely proposed; and though, in 1744, Boyle, perhaps as intelligently as any one before him, had attributed the heating of a hammered body to the transfer of the "motion" of the hammer to the ultimate particles of the body struck, yet the idea of the indestructibility of energy in all cases, and of course, therefore, in the mechanical excitation of heat, would not seem to have been expressly urged before the time of Rumford and Sir Humphry Davy.
In the mean while, however, a new doctrine was brought forth, assigning to heat a material existence and chemical properties. First
- Newton's "Optice," queries at the end of treatise, especially Nos. 6, 8, 12, 18, 23 and 31.
- The ideas of Huyghens on this point would seem to have resembled somewhat those of Galileo, already quoted. See "Exposé de la Situation de la Mécanique Appliquée," par Combes, etc., p. 200. Paris, 1867. And Locke quite uniformly made use of Bacon's hypothesis. See particularly his essay on the "Conduct of the Human Understanding Elements of Natural Philosophy," chap, xi., where he says:
"Heat is a very brisk agitation of the insensible parts of the object which produces in us that sensation whence we denominate the object hot; so what in our sensation is heat, in the object is nothing but motion. . . .
"On the other side, the utmost degree of cold is the cessation of that motion of the insensible particles which to our touch is heat."
- Hooke's "Micrographia," obs. xvi., 12th particular. "Posthumous Works," p. 49. "Lectures on Light," p. 116.
- "And now I speak of striking an iron with a hammer, I am put in mind of an operation that seems to contradict, but does indeed confirm our theory: namely, that if a somewhat longer nail be driven by a hammer into a plank or piece of wood, it will receive divers strokes on the head before it grow hot; but when it is driven to the head, so that it can go no further, a few strokes will suffice to give it a considerable heat; for while at every blow of the hammer the nail enters further and further into the wood, the motion that is produced is chiefly progressive, and is of the whole nail tending one way; whereas, when that motion is stopped, then the impulse given by the stroke being unable either to drive the nail further on or destroy its entireness, must be spent in making a various, vehement, and intestine commotion of the parts among themselves, and in such an one we formerly observed the nature of heat to consist."—(Boyle, "On the Mechanical Origin of Heat and Cold," "Complete Works," vol. iv., p. 236, et seq., exp. vi.)