208 THE POPULAR SCIENCE MONTHLY. 



Newton, 1 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 ex- 

 posed 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; 2 the works of Hooke par- 

 ticularly containing many and strong expositions of the vibratory 

 notion, and his comments on the mechanical and chemical produc- 

 tion of heat being urged often with as great clearness, and as sub- 

 tile a perception of occult natural causes, as any which we now 

 possess. 3 



But the adaptation of the known " laws of motion " to these opera- 

 tions, whereby heat might in many instances have been directly cor- 

 related to the energy expended in producing it, was not until long- 

 after definitely proposed; and though, in 1744, Boyle, 4 perhaps as in- 

 telligently 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 indestructi- 

 bility of energy in all cases, and of course, therefore, in the mechani- 

 cal 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, as- 

 signing to heat a material existence and chemical properties. First 



1 Newton's " Optice," queries at the end of treatise, especially Nos. 6, 8 12 18 23 

 and 31. 



2 The ideas of Huyghens on this point would seem to have resembled somewhat those 

 of Galileo, already quoted. See " Expose de la Situation de la Mecanique Appliquee," 

 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." 



3 Hooke's " Micrographia," obs. xvi., 12th particular. " Posthumous Works," p. 49. 

 "Lectures on Light," p. 1 10. 



4 " And now I speak of striking an iron with a hammer, I am put in mind of an opera- 

 tion that seems to contradict, but does indeed confirm our theory: namely, that if a some- 

 what 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 ; where- 

 as, 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.) 



