APPENDIX. 



345 



TABLE XL 



Dalton's Table of the Force of Vapor, from 32^ to 80^ 



Note to Table '^ll.—{Setnext'pagt.) 



To determine the dew-point, take two thermometers, the scales of 

 which agree, cover the bulb of one with thin muslin, and wet it with 

 water j swing both thermometers in the air, that they may be exposed under 

 similar circumstances, and note the height of the mercurial column in 

 each, after it has become stationary. Ascertain the difference between the 

 heights of the two columns. In the following table, find a number at the 

 top corresponding to the difference of heights, and in the left hand 

 column the degree answering to the temperature indicated by the dry 

 bulb thermometer ,• the figure at the intersection of the two lines is the 

 dew-point. 



Suppose, for instance, the dry bulb indicated 70=, and the wet bulb 

 6P ; 70 — 61 = 9, which is found at the top of the table ; in the column 

 beneath, and against 70=, is bb^, the dew-point. 



