[ 274 ] 



inches, Phil. Trans. 1777, p. 586. We may then affume the height 

 of 30 inches as the natural mean height of the barometer at the 

 level of the fea in moft temperatures between 32° and 82^ ; for 

 if the mercury were cooled down to ^2°, that is 23^ below 55", 

 it would be lowered by that condenfation only 0,07 of an inch ; 

 and if it were heated up to 80'', that is 25° above 55^2, it would 

 be raifedonly ,078 of an inch ; quantities which except in levelling 

 may be fafely difregarded. 



The French have heretofore confidered 28 Paris inches as the 

 mean height of the barometer at the level of the fea, that is 29,84 

 Englifh inches. But from 1400 obfervations made at Rochelle 

 by Fleaurieau De Bellvue, and from five years obfervations made 

 at Port Louis in the Ifle of France, he concludes the mean 

 heieht of the barometer at the level of the fea to be 28 inches 

 and 2 lines and 4-|. of a line in the temperatures of from 52° to 

 55° Fahr. =; 30,08 Englifh inches, 4 New Roz. p. 159*^. Hence 

 we may confider in round numbers 30 inches as the ftandard 

 height of biirometers at the level of the fea. And knowing the 

 true hti'^ht of any part of the earth, we may by fubtrading that 

 height exprefftd in fathoms from the log. of 30, viz. 4771,21, 

 find the logarithm which indicates the number of inches at which, 



as 



* La Chappe thought it 28 inches 1,5 lines. See Beguelin's Memoir, Mem. Berl. 

 1769. 12 Coll. Acad. 424. 



