568 



scale of temperature, simply the reciprocal of the temperature, mul- 

 tiplied by the mechanical equivalent of the thermal unit. If then 

 t denote the absolute temperature, which we have shown by ex- 

 periment* agrees sensibly with temperature by the air-thermometer 

 Cent, with 274 added, and if J denote the mechanical equivalent 

 of the thermal unit Centigrade, we have 



6 =JK- 



This expression agrees in reality, but is somewhat more conve- 

 nient in form, than that first given, Dynamical Theory of Heat, 4y, 

 Trans. R.S.E. 1851. 



Thus for water, the value of K, the thermal capacity of a cubic 

 foot under constant pressure, is 63*447, and e varies from to about 

 g^oo, for temperatures rising from that of maximum density to 50 

 Cent., and the elevation of temperature produced by an augmentation 

 of pressure amounting to n times 2117lbs. per square foot (that is 

 to say, to n atmospheres), is 



. 

 For mercury, we have 1390x28 -^ 8 



If, as a rough estimate, we take 



_t-2~8 I 

 46 X 2200' 



this become, 



If, for instance, the temperature be 300 on the absolute scale (that 

 is, 26 of the Centig. thermometer), we have 



n 



636 



as the heating effect produced by the sudden compression of water 

 at that temperature : so that ten atmospheres of pressure would give 

 gL of a degree Cent., or about five divisions on the scale of the most 

 sensitive of the ether thermometers we have as yet had constructed. 

 Thus if we take -g-gVo as ^ ie Vft l ue f e > this becomes 



t 

 103UOO ' 



* See Part II. of our Paper " On the Thermal Effects of Fluids in Motion," 

 Philosophical Transactions, 1854. 



