270 



Prof. Apjohn on a Formula for ascertaining 



Table IV. 

 March 25, 1835. 11 o'clock a.m. 



The results exhibited in the preceding tables will, I be- 

 lieve, be considered by many as going far towards establishing 

 the accuracy of my theoretical views. Although the depres- 

 sions vary from 4°*7 to 28°*5, the differences between the ob- 

 served dew-points and those deduced from the formula are 

 certainly not greater than what may fairly be ascribed to un- 

 avoidable inaccuracy of observation. But for the purpose of 

 putting this matter in a still clearer point of view, I have cal- 

 culated a number of values of m, the constant of our formula, 

 from the preceding observations. This was easily done; for 

 as all the observations in the same table refer to air in the 

 same hygrometrical state, each series should give the same 



dew-point, and the expression f — mdx~- must have in 



reference to them a constant value. f l — mdx -~r for one, 



oO 



must, therefore, be equal to F'-wD x -£- for any other, 



F —>fl 30 



an equation from which we deduce m = «r J x — . The 



application of this method gives us the following values of ?n. 

 Table 1. Table 2. 



r (l&2) 

 m = -01155 



(1&3) 

 •01185 



(2&3) x 

 •01075 



Table 3. 



(1&2) 

 m = -01489 



'(1&2) (1&3) (1&4) (2&3) (2&4) (3&4) A 

 m = -01137 -01187 -01309 -00825 -00976 -01045 



Table 4. 



(1&2) 



m = -00967. 



If the mean of all these values of m be taken, it will be 



found to be -01122, or the equivalent vulgar fraction ^ an 



approximation to the coefficient -g T employed in the formula 



which, under all the circumstances, cannot but be considered as 



