MR. W. N. SHAW ON HYGROMKTR1C MKTIKMiS 125 



0-480 (t-f) 

 JJ 610 -I 7 



This represents very satisfactorily the results obtained for fractions of saturation 

 exceeding '40. 



For values of t' below C. the number 610 must be replaced by 689. 



Observations by M. IZARN in the Pyrenees are quoted to show the applicability of 

 the formula at high-level stations. 



The second memoir (' Annales de Chimie,' vol. 37, 1853) is mainly devoted to the 

 discussion of the formula for reduction of psychrometer observations. 



AUGUST'S theoretical formula, recast and calculated with the new values of the 

 constants which REGNAULT was then able to supply (regarding the latent heat of 

 vaporisation of water at temperatures likely to occur in meteorological observations as 

 being constant and equal to 600), becomes 



x =/' 0-000635 (t t') H ; 



but, instead of using this formula for calculating his results, REGNAULT assumes the 

 form 



and determines the value of the constant A for psychrometers exposed in such situa- 

 tions as are likely to give rise to various conditions, by obtaining simultaneous readings 

 of the humidity by means of the chemical method. 



The mean results of his various series of experiments are given in the following 

 table : 



