[ 45^ ] 



Eighth, 



Barometer 30, what is the weight of a cubic foot of air iiii 

 this temperature (32°) ? 



We have already feefiJ-int -the firff exainple,' that 14,5 fathom 

 of 'air weigh 344,32 grains, and alfo premifed that one cubic foot 

 = 24- fathom. Now as 14,5. fathoni 344;32;; grairis-* :: 2'4. fath'om 

 569,99 grains (nearly 570 grains). Barometer 29,5 a cubic foot 

 of air weighs but 560,249 grains. See fecond Example. 



^^Note. — The weight'of 'a cable' foot of air in this temperature 

 being thus f6und barometer 30, the weight of a cubic foot of air 

 at any other barometrical height below 30 inches (=B) may be ' 

 found though not exadtly, yet very nearly, the difference not 

 exceeding half a grain, for as 30. B :: 569,99.x. Thus as 30.29,5 

 :: 569,99 to 560,49, which differs only by 0,241 from the truth. 



And if the barometrical height given exceed 3c inches, then as 

 B.30 :: X. 569,99. 



So alfo 144 ^Itidudinal feet on a bafis of one fquare inch, 

 weigh, barometer 30, 569,99 grains ; foalfo do 1728 cubic inches, 



Hh 2 from ■ 



