490 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



ity. It was even thought justifiable to suppose that in the case of heat, 

 produced by the friction of two bodies, these might suffer a diminution 

 of their heat capacity in consequence of the pressure. 



The physicists of that time were generally satisfied by the assumption 

 of a distinct heat substance, "caloric." There were always however 

 some few skeptics whose mind could not be set at rest by the sup- 

 position of an imponderable substance ; such as is the caloric. Among 

 their number was Count Rumford (Benjamin Thompson), clear-headed 

 and acute thinker, unprejudiced investigator, eminent observer and dis- 

 tinguished experimentalist, as he was. In the first place he tried by 

 delicate weighings (1798) whether in fact very hot, non-oxidizing bodies 

 (for instance a ball of gold, or a quantity of water hermetically inclosed 

 in a glass ball), compared with their weight in the cold state, might per- 

 haps show a slight increase of weight; the tests resulted in the nega- 

 tive. Though the defenders of the caloric matter could have raised the 

 objection that this substance was so rare that it would not act even on 

 the most sensitive scales, they however seized upon another one ; they 

 declared weight to be a non-essential quality of matter, and they called 

 substances without gravity " imponderables." Among these they counted 

 hypothetically caloric and light, and also the electric and magnetic 

 fluids. Weight could not be supposed to be an attribute of these im- 

 ponderables for the very reason that they were observed to proceed 

 with equal force in all directions and not, like ponderable bodies, only 

 toward the earth. 



Rumford was particularly confirmed in his disbelief of the existence 

 of the caloric by the manifestation of great quantities of heat conse- 

 quent upon the friction of bodies. It had long been known that augers, 

 saws, files, brakes, ungreased axles, pivots, &c. became heated to a 

 considerable degree by the friction they undergo in use. Every turner 

 was aware of this fact, and by simply using the heat produced by the 

 severe^friction for making black or brown stripes on his productions by 

 charring, he thereby bestowed a permanent ornament. Tlu> emission 

 of sparks in grinding knives, the fire kindling by friction among un- 

 civilized nations, friction matches, as also the needle-guns of civilized 

 nations, belong to their number. The adherents of the material 

 theory of heat, as indicated above, had recourse to the supposition 

 that in friction bodies were condensed and their heat capacity was 

 therefore diminished; the consequence of this would be that a part of 

 the heat would become free and escape. One problem remained how- 

 ever unsolved, namely, how this should be possible, considering the 

 inexhaustible product and the comparatively small amount of pressure. 

 This question presented itself very forcibly to Rumford when he (1798) 

 observed the enormous amounts of heat becoming free in the chilling of 

 cannons, where the metal-shavings which fell off became particularly 

 heated. As he did not find the heat capacity of the shavings dimin- 

 ished any more than that of the solid metal of the cannons, the heating 



