488 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



water vessel, and but 1 under that containing the quicksilver. For the 

 same reason 33 times the quantity of coal would have to be burned under 

 the water that the quicksilver would require, if the temperature of these 

 fluids were to be increased to the same degrees of heat. 



Because quicksilver requires only 3^ of the quantity of heat which is 

 required by water to raise its temperature one centigrade degree, the 

 quicksilver will, if equal quantities of these fluids are placed on a 

 heated stove in separate vessels, acquire a higher temperature in a much 

 shorter time than the water. If however equal quantities of water and 

 quicksilver, the temperature of which has been raised in this manner, 

 are both allowed to cool and are put in a place having a constant tem- 

 perature the temperature of the quicksilver will fall much more rapidly 

 than that of the water, for the reason that the latter, on account of its 

 33 times greater specific heat, has to give back again this 33 times 

 greater amount of heat for every degree of falling temperature, which 

 had previously been absorbed by it for each 1° C. of heat. Under other- 

 wise similar circumstances the temperature of a body possessing but a 

 small degree of specific heat rises or falls more rapidly than that of a 

 body possessing a higher degree of the same. The difference in the 

 amount of the specific heat of different bodies is not directly apparent; 

 the existence even of specific heat has to be determined, as was pre- 

 viously observed, by peculiar mixture tests or other processes. Though, 

 from other considerations than the above, the varying heat-conducting 

 capacity of bodies (causing their more or less rapid heating and cooling) 

 was known, the existence of specific heat was for a long time unknown 

 to natural philosophers. Indeed, it was only discovered as late as 

 17G0-17G.") by Hie Scottish professor of chemistry, Joseph Black. The 

 discovery was made during his researches concerning another important 

 law of heat discovered by him, of which more hereafter. Black discov- 

 ered the fact which is now accepted as specific heat. The designation 

 of this fact as "specific heat," however, originated with Wilke (1772). 

 Crawford (1779) used the expression "comparative heat" or heat 

 capacity. The latter word refers figuratively to the varying capacity of 

 different bodies, by virtue of which they absorb different amounts of heat 

 for each 1° of increased temperature. 



1 1 had not escaped the notice of the discoverer of specific heat that an 

 equal quantity of heat absorbed by a body tor each degree of increased 

 temperature, and (so to speak) concealed in it, is given back at exactly 

 the same rate when the temperature of a body decreases oue degree. 

 What becomes of the heat absorbed by bodies in the increase of their 

 temperature, and which is given back so precisely in the process of cool- 

 ing! This is about the question Black asked, and in order to arrive at 

 a correct answer he examined the two principal theories in regard to 

 the ultimate cause of heat which at all times had been more or less 

 obscurely expressed. 



The ancient philosophers, in explanation of heat phenomena, had as 



