from the Indications of the Wet-bulb Thermometer. 55 



In Dr. Apjohn's I omit the barometrical column, which 

 Dr. Mason finds to be needless (p. 101), and that of the cal- 

 culated dew-points, in which the error is generally on one 

 side, occasioned, as the author supposes, by an error in one of 

 the elements; and I substitute, for the sake of comparison with 

 Mason's, a column (5) of differences between the dew-point 

 and dry bulb thermometer; having for the same purpose 

 changed the order of arrangement to that of these differences. 



In Mason's table such numbers only are taken as come into 

 comparison with Apjohn's; and to facilitate this comparison, 

 three columns (6, 7, 8) interpolated, illustrating his method 

 of obtaining the dew-point, viz. doubling the difference be- 

 tween the wet and dry bulb (col. 8), + a correction for wind 

 (col. 7)> and deducting the product (col. 10), from the indi- 

 cation of the dry-bulb thermometer. 



Now it is remarkable that if instead of adding this correc- 



