442 Lieutenant Eenny on a new Barometric 



With respect to the laws of variation of forces of aqueous vapour, it appears, on 

 consulting the Table of Forces of Aqueous Vapour in Tuenee's " Chemistry" 

 (seventh edition, pp. 1248 and 1249), that such forces form quam proxime 

 a geometric series, when the temperatures form an arithmetic one. As, there- 

 fore, we assume the arithmetic mean to replace the variable ( T— 32), 



we can do nothing better to replace our variable F than to assume, as its re- 

 presentative, the geometric mean of forces of vapour, viz. -/{ff')- 

 Making such substitutions in equation (3), we have 



d-n — gr^ dz 



Integrating equation (4), we have 



hyp. log (.-§/(//) = g+ , . + ^_64r -(7TIT- 



a 1 + ' Ik 



(4) 



Replacing successively in this last equation the quantity tt, by its values at the 

 lower and upper stations, viz., f and 77'; z by its corresponding values h. and 

 (h-\-H); substituting for hyperbolic logarithms common ones, and subtracting 

 one equation from the other, we have, after suitable modifications, 



H = — ^i TT — ^ .{1 + -— ^— + -^^ — -, • com. log ^, ? //;{/ 



Mg \ r r- \ p-%viff) 



Omitting in this last equation the quantity -^ ^ ^^ ^°° ^^^^^^ *° ^^ ^^^^" 



a 



fully retained, and assuming K^ to represent the quantity -^, we have 



. P- _ 



^. ^ ,1 ^,'±1:^! . jl + ?Lt^i .com.log^-^^^^) 



