[ 472 ] 



Thus in iho above cafe the fundamental difference was 37,4, 



and the approximate height is 2603,1 feet. Now 37li>< iL_ = 



45° 



219,8, which added to 2603,1 = 2819 feet. 



-The error is 12 feet, and fcarce ever exceeds by 40 feet the re- 

 fults of other methods. 



2d°. To find the height or number of inches at which mercury 

 would ftand on a given elevation true to five-tenths of an inch, 

 when that altitude does not exceed 19700 feet, the height of the 

 mercury below being given. — Add to the given altitude, that op- 

 pofite to the given barometrical height. The altitude neareft to 

 the fum of both will point out the barometrical height fought. 



' Thus the height of Mount Blanc being 14624 feet above Mr. 

 Sencbier's cabinet at Geneva, and the height of the lower baroine- 

 ter being 29,1 (Englifh), a barometer at the top of that mountain 

 Avas found to ftand at 17 inches — And by this calculation it flood at 

 16,6, foroppofite to 29,1 we have 2475. -'^"•^ 14624+2475=17099. 

 The nearefl tabular number to this is 17 102, which denotes 16,6 

 inches of mercurj^. The error then is 0,3 of an inch. — But in ge- 

 neral it is much fmaller ; thus, in meafuring the Mole, whofe 

 height is 42 11 feet, Schuckburg found the lower barometer 28,1, 



&c. 



