334 On the Hygrometer. 



c c' 



and a' formerly assigned, it is evident that - = a and - = a' 



s s 



Hence, by substitution, 



^ V(|) 



SX 



=:</Q=-VG)=- 



30 



Introducing the above value of a' into equation (1.) it be- 

 comes 



/.-^-^>/(l)=4 <^-> 



or 



/*'_.011448D^/(^)=/,, 



by making a = .2669, and Z = 1119. 



With respect to the correction for difference of pressure, the 

 author stated in his former paper, that the formula there pro- 

 posed gave correct results between the pressures of 30 and 22.9, 



B + 27 



when D was multiplied by 



57 



Although, as it appears, 



this coefficient was adopted through a misunderstanding of what 



Mr Meikle had stated, yet, if v/ ( ^ ) be the coefficient which 



is truly deducible from theory, the accompany- 

 ing Table will explain how the other agreed so 

 well with observation ; for it is evident that, 

 at least as low as 22 inches, it would be in- 

 different whether the Table of Corrections 



were calculated by means of y ( — ) 



B+27 



or 



57 



And here it ought to be remarked. 



that the numbers in the small table formerly 



given are rather too large, an additional 



correction having been joined with them, 



with the view of obviating a source of error, 



which, upon more careful consideration, it is found can have 



no sensible effect. The subjoined is the correct Table : the 



manner of using it is explained in the former paper. 



