372 Mr. J. A. Calantarients on a New portable 



Temperature. 



( 52= -0-16, 

 64= -005 



Mean correction at J 



i 74= —0-00 

 \ 84= +0-04 

 94= +007 

 104=+ 0-08 j 



pressure remaining 

 constant. 



Description of the Barometer. 



This instrument, as represented in figs. 1 and 2, consists of 

 three parts : — 



1st, of a glass tube (fig. 2, ABC) of small diameter, bent at 

 C and ending in the closed bulb D ; 



2ndly, of a tube (E F G) of larger diameter, joined to the first 

 at E A and open to the atmosphere at G ; 



3rdly, of a cylinder (HKL) joined to the first two at H and 

 closed at L. 



These three freely communicate with one another at E A H. 

 The black spaces ending at B F K indicate the parts filled with 

 mercury, the remainder of the tube ABC and the bulb D con- 

 tain air slightly rarefied, and the remaining space in the cylin- 

 der K L is filled with liquid sulphuric ether. 



From this arrangement it is evident that any variation in the 

 atmospheric pressure would be communicated to the column of 

 mercury FAB through the open tube G F, and the rise or fall 

 of the point B indicate the exact degree of such variation. This, 

 therefore, would form a barometer. 



Now with regard to the effects of temperature. The cylinder 

 HKL has been made in such proportion to the bulb D and the 

 tube above it, that the ether and mercury contained in the first 

 have the exact expansive power necessary to counteract that of 

 air in the latter. For instance, suppose the temperature were 

 to rise, the expansion of air in the tube and bulb BCD would 

 tend to lower the point B ; but as the ether and mercury in the 

 cylinder also expand at the same time and drive mercury into 

 the tube E F G, the weight of this additional column would tend 

 to raise the point B ; and as these two forces are equal and op- 

 posite in direction, the point B would remain stationary. If the 

 proportion between the two is not exactly equal, it is easily re- 

 stored, either by exchanging mercury for ether, or the contrary, 

 as the case may require, in the cylinder HKL, or by varying 

 the quantity of air in the bulb D. 



The two contractions at the lower end of the cylinder are in- 

 tended to prevent the ether escaping when the instrument is laid 

 on its side. 



