[ 111 ] 



XVI. On the Mechanical Action of Heat % William John 



Macquoen Rankine, C.E., F.R.SS. Land, and Edtnb. ^c. 



[Continued from p. 21.] 



Section IL— Of Real and Apparent Specific Heat, especially 



in the State of Perfect Gas. 



(9 ) rpHE apparent specific heat of a given substance is found 



^ ^^ 1 by adding to the real specific heat (or the heat which 



retains its fom in producing an elevation of one fgree of em- 



neratui-e in unity of weight) that additional heat which di.ap- 



S as m producing changl of volume and of molecular an;ange. 



men and which is represented by Q' m equation 6 of Section L, 



Tnd taking its ,o^«/diLentialcoeflicient with respect o the ^em- 



perature. Hence, denoting total apparent specific heat by K, 



, dQ dM' dQ^dO! dQi,d_Y 



= c^l-2^ + ^^-'^^'^vv dy) dr)j 



Another mode of expressing this coefladent is the following :— 

 Denote the ratio I 



Sal^y^' [ (14) 



and the real specific heat by 



fe— 1— 



Then 



L,(.,K.-,(f(l-§)-f)}. ■ <-) 



The value of — is to be determined from the conditions of 

 each particular cale; so that each substance may have a variety 

 of apparent specific heats, according to the manner m which the 

 volume varies witli the temperature. ^^ 



If the volume is not permitted to vary, so that -^ =0, there 

 is obtained the following result, being the apparent specific heat 

 at constant volume : — 



1/1 , .d\]\ 



= .(l-N(.-.)f). . . . • • (16) 

 (10.) When the substance under consideration is a perfect 



