437 
that the sum of its sensible and latent heat is at every tem- 
perature a constant quantity,—equation (II) becomes 
f" =f! — 01185 (t— ) x pa. ; (IV) 
and equation (III) becomes 
fl af’ — 01017 (¢ — t) x? = (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 
probability, 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 ¢’ is greater than 32°, I 
have calculated 54 values of the coefficient, by methods to 
the explanation of which I now proceed. 
*‘], Representing the coefficient in question by m, the 
hygrometric formula becomes 
/ 
ida) ee a, P csi 
S' =f —m(t—t) x 307° 
Now if air, in reference to which ¢ and 7’ have been accu- 
rately noted, be raised to any higher temperature, and the ob- 
servation repeated, we obtain data for determining the value 
p—f' 
307? for 
of m. For f” being constant, f’ — m (t — t’) x 
: : p— F’ 
one observation, will be equal to r/ — m(r —T’) X ag 
