182 

 TABLE XIV' 



Mr. Glaisher published in London, in 1856, another series of Hygrometrical Tables, 

 which were unknown to the writer when the Second Edition of this volume was 

 issued. They are based on Regnault's Table of Elastic Forces of Vapor, and on the 

 coefficient of the expansion of the air as determined by the same physicist. The 

 Psychrometrical Table, however, is not computed from Regnault's formula, but by 

 first finding out, in the manner described on page 140, the temperatures of the dew- 

 point from the readings of the Psychrometer, by means of the empirical factors given 

 below, in Table XIV'., and then taking the corresponding values of the force of 

 vapor from Regnault's table. These factors have been derived from the combination 

 of all simultaneous observations of the dry and wet bulb thermometers with those of 

 DanielPs hygrometer, taken at the Royal Observatory, Greenwich, from the year 

 1841 to 1854, with some observations taken at high temperatures in India, and others 

 at low and medium temperatures at Toronto ; they are, therefore, more correct 

 than those given in Table XIV. page 140. The results in this new Psychrometrical 

 Table, nevertheless, by no means entirely coincide with those given by the formula, 

 as a comparison with those in Table VII. will show. 



xiv'. 



FACTORS TO FIND OUT THE TEMPERATURE OF THE DEW-POINT FROM THE 

 READINGS OF THE PSYCHROMETER. GlAISHER. 



B 



146 



