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 zz the height of the centigrade thermometer. 

 p zz the height of de Saussure's hygrometer. 

 Let a zz \ 



b zz f the quantities indicated in the columns of the fol- 

 c zz f lowing table, and designated by the same letters. 



<p zz 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 

 p degrees is <p (0-015 p — 0.47), while p > 50°. Let 0'015 

 [a — 0*47 = m. 



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



met. 



<p zz 0-005123 X (10) t - °^W»— ; + 3O ' O0O06w83 ' 

 (M4c. cel. t. iv. p. 273.) Hence it is concluded : 



19*? 1*8 millim. 



a = ® — — : b zz a X m : c zz <p 42 ; and d s= c 



y 1 + t. 0 00375 



(l-m). 



