437 



that the sum of its sensible and latent heat is at every tem- 

 perature a constant quantity, — equation (II) becomes 



/" =/' - -01 135 {t - t') X ^^ ; (IV) 



and equation (III) becomes 



/"=/'- -01017 (<-<0x 2^. (V) 



" The theory which has led to these conclusions is now 

 universally admitted to be correct ; but as doubts may 

 be entertained respecting the exactness of the coefficient, 

 whose value, as has been seen, depends on the numbers by 

 which a and e are represented, (numbers which are, in all 

 probabiHty, not as yet known with great precision,) it would 

 appear desirable to deduce its value directly from experi- 

 ment. This is the immediate object of the present commu- 

 nication. 



" In my second paper on the dew-point, I have given three 

 distinct series of experiments, applicable to such a purpose; — 

 the first relating to air whose dew-point was determined by 

 Daniell's instrument ; the second to air perfectly dry ; and 

 the third to air whose dew-point is known with certainty, 

 and without the aid of any form of condensation hygrome- 

 ter. From these, in all of which t' is greater than 32% I 

 have calculated 54 values of the coefficient, by methods to 

 the explanation of which I now proceed. 



" 1. Representing the coefficient in question by m, the 

 hygrometric formula becomes 



rz^/~m(/-OX^^^ 



Now if air, in reference to which t and t' have been accu- 

 rately noted, be raised to any higher temperature, and the ob- 

 servation repeated, we obtain data for determining the value 



oim. ¥oYf being constant, f -m{t'-t')X ^^-^ y for 



one observation, will be equal to f' — m (t — • tO X 



30 



