126 



MR. W. N. SHAW ON HYGROMETB1C METHODS. 



The conclusion which REGNAULT draws from these series of observations is that 

 the psychrometer may be satisfactorily employed, and give the fractions of saturation 

 to within one-fortieth, provided that it be regarded as an empirical instrument. The 

 instrument should be protected from the direct action of the wind, and its indications 

 should be interpreted by means of a formula similar in form to the one given, the 

 constant A being determined for each locality where observations are to be taken, 

 and, if necessary, a different value should be taken for different parts of the scale. 



A series of experiments to compare the indications of the psychrometer in a closed 

 room with the results of the chemical or BRUNNER'S hygrometric method was made by 

 VOGEL (' Abhandlungen der MUnchener Akadernie,' vol. 8, 1860, p. 295). The wet 



* For degrees of saturation above '7 the number quoted is apparently too small for ice-covered bulbs. 

 The number A = G'0013 would have been more suitable for such observations, 

 t Experiments of M. IZARN. 



