METEOROLOGY. 513 



In this reasoning (of August, Apjohu, and Maxwell) no attention has 

 been given to the iuflueuce of radiation ; if one had considered this, then, 



however, Cbistoni ascribes to it high importance, I will show that it also 

 reduces to the formula given in the text : 



Belli starts with the masses of air and the vapor instead of with the 

 weight, as did August. Let m be the total mass of both; the ratio of 

 the masses of air and aqueous vapor is as P— p to p ff so that the mass 

 of the air is 



m (P—p ) 

 P — fo+i>off 

 and the mass of the vapor is 



mp ff 



P — Po + Po <r 

 and the sum of both is m. When the air has cooled to <', and becomes 

 saturated with vapor, then the new vapor-mass p x is to the mass of air 

 which has remained unchanged, and is still 



m (P —p ) 



¥—Po+PoG 

 as Pi 6 is to P — p x : whence 



Pl ~ m & G P-ffo 



P — p +p off - P_ Pl 



and therefore the mass of the newly developed vapor is 



v-p + Poa ( K w=p-; Pl - p °J 



we have, therefore, as the equation for the permanent maintenance of 

 this condition 



(p-^f^ 1 ~P^) Xff = t( p -Po) S + P»<? k] ( t - V) 

 or 



Since, now, ^ — i- ft , is only a little larger than unity and is in the most 

 P— j?i 

 unfavorable case 1.01, and since the expression 



i-?(i-£) 



is also, as before shown, only a little greater than unity, we can, there- 

 fore, certainly replace each by 1 considering that in the result for p the 

 hundredth part can never be exact and is not even necessary, ami thus 

 there remains again the expression given above in the text. 



I have not disdaiued this presentation, trivial as it may seem, because 

 it frequently seems as though a psychrometer formula is considered as 

 better the more complicated it is, and especially because Cbistoni only 

 recently (see his treatise above cited) has claimed for the formula of 

 Belli an advantage over that of August, and declared it as the best that 

 at present exists. 



The formula of August, as well as that of Belli, are both based on the 

 consideration of convection, and by omitting the radiation give abso- 

 lutely the same result. Therefore, theoretical considerations will not 

 prove the more complicated formula to be the more accurate. 

 H. Mis. 69 33 



