[ 438 ] 



Here loooo feet=i666,66 fathom. And the log. of 20,439 is 3 10459. 

 Now 3104594-166666 = 477125 which correfpond with the 

 natural number 30. This then is the mercurial height in the 

 lower barometer. 



Corollary. __ 



Hence an elevation, and the mean temperature of 32*^ being 

 given, the height at which two barometers would ftand may be 

 foiTnd, if the height of either be alfo given ; otherwife the 

 problem is undeterminate, and recourfe mufl be had to the ge- 

 neral pofition, that the mean height of a barometer ftanding at 

 the level of the fea is 30 inches. 



But 7iote. — That if the height of the mercury in both baro- 

 meters be not equal, they muft be equalized as to that cir- 

 cumftance, by extracting the excefs of one over the other, 

 arifing from the expanfion of mercury by heat. The method I 

 employ of effedling this equation is fimilar to that devifed 

 by Dr. Horfely ; namely, by fubftrading the degrees of heat of 

 the colder barometer, from thofe of the warmer, and multi- 

 plying the difference into o,+o, and fubtradling this product from, 

 the difference of the logarithms^ 



PROBLENf 





