528 Mr. Pembrey on Comparative Experiments 



The aspirator used was that described in the paper pre- 

 viously mentioned*. The aspirating-bottles were covered 

 with felt, so that the temperature of the water generally 

 varied only a tenth or two of a degree Centigrade, never 

 more than half a degree, during the period of observation. 



The volume of air aspirated has always been corrected for 

 temperature, aqueous vapour, and barometric height. 



In calculating the tension of aqueous vapour from the 

 chemical determinations the table given by Shawf has proved 

 very valuable. 



The preceding Table (I.) shows that the amounts of moisture 

 calculated from the psychrometric readings by Glaisher's 

 Tables vary, when compared with the gravimetric determina- 

 tions, from —5 per cent, to +7 per cent. The mean, how- 

 ever, is '0130 to '04:26 grm., or less than +1 per cent, for 

 the psychrometer. 



The tensions given by the chemical determinations have 

 been calculated, and are compared in Table II. with those 

 obtained from the psychrometer by means of Glaisher's, 

 Haeghens', Guyot's, and Wild's tables. 



Table II. 





Experiment. 



Chemical 

 method. 



Psychrometer. 



Glaisher. 



Haeghens. 



Guyot. 



Wild. 



1 



millim. 

 345 

 2-60 

 2-49 

 2-56 

 375 

 4-03 

 3-70 

 3-75 

 4-87 

 4-95 

 4-85 

 486 

 4-05 



millim. 

 3-20 



2-67 

 2-36 

 2-36 

 3-83 

 4-06 

 363 

 3-78 

 4-85 

 4-85 

 4-87 

 4-98 

 3-86 



millim. 

 344 

 2-73 

 2-58 

 2-70 

 401 

 4-20 

 3-80 

 3-84 

 4-84 

 4-84 

 4-86 

 4-97 

 423 



millim. 



345 

 ' 2-72 

 2-56 

 2-64 

 3-98 

 416 

 3-78 

 3-81 

 4-82 

 4-82 

 4-82 

 492 

 3-96 



millioa. 

 3-47 

 2-73 

 2-57 

 261 

 3 93 

 4-11 

 373 

 3-83 

 4-83 

 4-80 

 4-80 

 5-00 

 4-17 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 





Mean 



3-84 



3-80 



3-93 



3-88 



3-89 





In order to make this paper more complete, the cor- 

 responding tables of the previous experiments are here 

 reproduced. 



* Phil. Mag. April 1890, p. 309. 



t ""On Hygrometric Methods/' Phil. Trans. 1888. A. 



