90 



thickness, admitting in the air the quantity of 

 vapor indicated by the hygrometer*. 



* The following is the basis of Mr. d'Aubuisson's calcula- 

 tion : 



t z= the height of the centigrade thermometer. 

 (A — the height of de Saussure's hygrometer 

 Let a =*) 



b 2r f the quantities indicated in the columns of the fol* 

 c —C lowing table, and designated by the same letters. 



<p ~ Elastic force of the vapour in a space which is sa- 

 turated. 



According to the observations of Saussure, it is found, that 

 the elastic force, in a space in which the hygrometer marks 

 (A degrees is f (0-015 /x —0.47), while p > 50°. Let 0*015 



yu C47 2= 771. 



Mr. La Place gives, from the experiments of Dalton, 



met. 



<P — 0 005123 X (10) t -° , ° 2 W' 2 J_30-00O062i63, 



{M4c. c&. t. iv. p. 273.) Hence it is concluded : 



1221*8 niillim. 



a = 0 ' ; b zz a X m ; c = <p 42 ; and d = c 



y 1 + t. 0 00375 



(i — m). 



