122 



BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 8 Fig. 609- 



iliii 



the higher we ascend the rarer it be- 

 I comes. At 31 inches a fall of one- 

 W tenth of an inch indicates a height of 82 

 feet; at 30 inches, 85 feet; at 29 inch- 

 es, 87 feet; at 28 inches, 91 feet; at 

 27 inches, 94 feet ; and at 26 inches, 

 98 feet ; for every tenth of an inch the 

 mercury falls. 



Price, - $20.00. 



" with corrections for 

 level in reservoir, 

 and extra finish, $25.00. 



Pike's Mountain Barometer for Aca- 

 demies. (Fig. 608.) This is an instru- 

 ment similar in its construction to the 

 preceding one, but of a larger make ; the 

 case being two inches in diameter, hav- 

 ing a brass cover to the scales, and the 

 reservoir of mercury being so large as 

 to make it unnecessary to use any cor- 

 rection for the level, and is inclosed 

 in a brass case with portable screw 

 covered with a cap screwing on. The 

 barometer scales extend to twenty-five 

 or twenty-six inches, which will allow 

 of the measurement of a height of 4000 

 feet or over. This is a stout and well 

 made instrument, the brass work highly 

 polished, and the demand for them has 

 enabled the maker to sell them at a 

 very low rate. 



Price, - - $10.00. 



" with vernier, $12.00. 



Standard Barometer. (Fig. 600.) 

 This consists of a tube of unusually large 

 size filled with mercury, and inverted in 

 a large glass reservoir also containing 

 mercury, the top of which is exposed to 

 the atmosphere, and covered by a 

 wooden cap, through which a pointed 

 steel rod passes, fastened to a projection 



