168 THOMSON ON CARNOT'S 



" foot-pound ;"and the unit of heat that quantity 

 which, when added to a pound of water at 0, will 

 produce an elevation of 1 in temperature. The 

 mean value of /* for any degree is found to a suffi- 

 cient degree of approximation by taking, in place 

 of (r, dp/dt and k ; in the expression 



the mean values of those elements; or, what is 

 equivalent to the corresponding accuracy of ap- 

 proximation, by taking, in place of cr and k respec- 

 tively, the mean of the values of those elements for 

 the limits of temperature, and in place of dp/dt, 

 the difference of the values of p, at the same limits. 



35. In Regnault's work (at the end of the eighth 

 memoir), a table of the pressures of saturated steam 

 for the successive temperatures 0, 1, 2, ... 230, 

 expressed in millimetres of mercury, is given. On 

 account of the units adopted in this paper, these 

 pressures must be estimated in pounds on the 

 square foot, which we may do by multiplying each 

 number of millirnetre3 by 2.7896, the weight in 

 pounds of a sheet of mercury, one millimetre thick, 

 and a square foot in area. 



36. The value of &, the latent heat of a cubic 

 foot, for any temperature t, is found from A, the 



