960 
Proceedings of the Poycd Society 
the results deduced from Apjohn’s formula are too high, there being 
no change in the direction of the lines. In most works on Meteor- 
ology we find that for temperatures below 32° F. the value is 
given for m, but I have not been able to discover the origin of this, 
and it is not stated whether the change is to be made with reference 
to the temperature of the dry bulb or of the wet bulb. Using this 
value we get dew-point differing still further from my own observa- 
tions, and also from Glaisher’s tables. 
The empirical formula deduced from the diagram is simply that 
of Apjohn, the factor denoted by k being ecjui valent to 
The value of 
1 . 25-3 1 
87 * 30-0“ 103 5 
and the temperatures at which the formula is found to give most 
accurate results are those at which the value of K is nearest T Jg-. 
It is obviously impossible to reproduce the diagram in full, but 
a specimen is given for wet bulb temperatures between 15° F. at 
20* F. The lines for Glaisher’s tables (solid) and Apjohn’s formula 
(dotted), are given for each degree of temperature of wet bulb, and 
the mean direction given by the hygrometer observations is shown 
for wet bulb temperatures of 15®*5 F., 16°*5 F., and 19**4 F. 
