JTATE 0E VAPOUR SUBSISTING IN TttE ATMOSPHERE. 



243 



be recolle&ed that Mr. Sauflure found that a cubic foot of dry 

 air in reality took up 11,069 grains of mofture when faturated 

 at this temperature, and that it was only by way of conceflion 

 to thofe againft whom he argued, that he ffoted the weight 

 taken up at 10 grains; then we mould have of 11,069 to 

 2 1 , 1 95, or in round numbers as 1 1 to 2 1 or 1 to 1 9. And it 

 mould farther be remarked, that the temperature is given very 

 loofely, for it is ftated to be from 14 to 15 or 16 degrees of 

 Reaumur. See Hygrometer , p. 104 and 284. 



Sauflure has given us a table, by the help of which the ab- Table of the 



folute quantity of vapour at any barometrical height, in a cubic <l uant . lt,e ^ of va " 



r > • • i • r 1 pour ,n a,r °* 



foot of air being known, the proportion and abfolute quantity different den- 

 in a cubic foot, at another barometrical height, 3,6 inches fitles but hkc 

 lower, may be known from the mercurial height 28,77 to that 

 of three inches and one*half, nearly. 



This table I here give, adapting it to our meafures. 



Thus fuppofing the abfolute quantity 

 of diffblved vapour at any temperature, 

 and barometer 28,77 to be 10 grains per 

 cubic foot, then the quantity of vapour 

 at a height at which a barometer would 

 ftand at. 25, 17 inches would be 10 x 

 0,9528 = 9,528 and at the height at 

 which a barometer would Hand at (even 

 inches, the quantity in a cubic foot would 

 be only 10 X ,6230 = 6,23. But flilt 

 it is fuppofed that at thofe great heights, at which barometers 

 would Hand fo low, that the air is of the fame temperature as 

 the original experiment is made at, namely in this cafe, as it 

 is found at barometer 28,77 inches ; but fince in reality air at 

 great heights is generally much colder than below, to afcertain 

 the real proportion of vapour at thofe heights it will be necef- 

 fary to find the quantity of vapour which a cubic foot of air is 

 capable of holding at that temperature barometer 28,77, and 

 the ratio which the quantity or weight of vapour actually found 

 bears to the complement at that temperature. Then, 2. to 

 find the complement of a cubic foot of air at the temperature 

 which prevails at the given barometrical height, and diminifh it 

 in the fame ratio in which it was found diminiihed below, and 

 finally diminifh it ftill farther in the ratio which that barometri- 

 cal height demands. An example will fully explain this rule. 



R 2 Thus 



