320 



the well-known principle of barometric measurements ; and by 

 consulting the table of forces of aqueous vapour, in the ap- 

 pendix to Turner's Chemistry,* 1 find that the forces of va- 

 pour form {gicam proxime) a geometric series, when the de- 

 grees of temperature form an arithmetic one. Let us, therefore, 

 take the geometric mean of the forces of aqueous vapour at the 

 stations = V (/x/')> and indicating this quantity F, and instead 

 of the variable forces of vapour in the last equation, let us 

 employ the quantity F' (which will be practically suflBciently 

 accurate so long as the correction for the temperature of the air, 

 as shown by the detached thermometers, continues, as at pre- 

 sent, so liable to error), we shall change our fundamental equa- 

 tion, as given above, into 



V=- .< 1 7+1 



n V p 



F ^ F , F 



— + 1 - -^, + 1 - -^, 

 rp r^p r-^p 



-&c. 



— I 



f = - J n- F[-+ — ,+ ^r-,+ -rr, + &c. . . —-T~' r • 

 n\ \p rp r^p r^p ?•"' ^ pj J 



Summing the geometric series of the right hand of the equa- 

 tion last obtained, and modifying somewhat the rest of it, we 

 have 



v = v' \ 1 -F 



J_\1 



1 

 r 



(A) 



Butr" '^ p =p; eliminating r from equation (A), by means of 

 this last equation, we have 



Let us now seek the limit of the right hand side of equa- 



• Seventh Edit. pp. 1248-49. 



