166 THOMSON ON CARNOT'S 



find a value of /* for every temperature within 

 practical limits. The special character of the ex- 

 perimental researches, whether with reference to 

 gases or with reference to vapors, necessary and 

 sufficient for this object, is defined and restricted 

 in the most precise manner, by the expressions (6) 

 for //, given above.* 



33. The object of Regnault's great work, referred 

 to in the title of this paper, is the experimental de- 

 termination of the various physical elements of the 

 steam-engine ; and when it is complete, it will 

 furnish all the data necessary for the calculation 

 of /*. The valuable researches already published 

 in a first part of that work make known the 

 latent heat of a given weight, and the pressure, of 

 saturated steam for all temperatures between 

 and 230 Cent, of the air-thermometer. Besides 

 these data, however, the density of saturated va- 

 por must be known, in order that k, the latent 

 heat of a unit of volume, may be calculated from 

 Regnault's determination of the latent heat of a 

 given weight. * Between the limits of and 100, 



* It is, comparatively speaking, of little consequence to 

 know accurately the value of or, for the factor (1 cr) of 

 the expression for >w, since it is so small (being less than 

 T ^ for all temperatures between and 100) that, unless 

 all the data are known with more accuracy than we can 



