Mr. H. Russell's Description of a Pressure Gauge. 93 



notice a description of a pressure gauge which I have con- 

 structed for my own amusement, and which I have no doubt 

 will ultimately be considered as remarkable for its accuracy 

 and simplicity, as Mr. Seaward's will for its inaccuracy and 



complexity. . . . 



The o-auo-e which I am now about to describe, and which is 

 here represented, consists of a glass tube sealed at one end 

 with a ball blown very near the other, leaving only as much 

 tube beyond the ball as may be necessary for connecting it 

 with the pipe leading from the vessel containing the condensed 

 gas, steam, or other elastic vapour. This ball, when the tube 

 is filled with air and subject only to atmospheric pressure, 

 should be about three quarters full of mercury, and the whole 

 capacity need not exceed that of the tube more than as two 

 to one. That the divisions on the scale may be in geometri- 

 cal progression, the tube is placed in a horizontal position : 

 this renders the instrument altogether so simple in appearance, 

 that persons totally unacquainted with instruments of this de- 

 scription, may at once be brought to understand its nature, 

 and be enabled to affirm with confidence the degree of pres- 

 sure to which it is subject. 





To determine the degree of pressure at any given point, 

 ascertain the distance of that point from the sealed end of 

 the tube, and by that measure divide the length of tube con- 

 tained between the sealed end and the bulb ; the quotient will be 

 the number of atmospheres. Thus, in general terms, where T 

 represents the whole tube, P the part into which the column 

 of air is compressed, and A the number of atmospheres ; we 

 have — = A. Thus suppose the tube eight feet long, and 

 the column of air compressed into half that length, then we 

 have 1=2 atmospheres. If this column be again compressed 

 into half its volume, it will be represented by f = 4 atmo- 

 spheres. If again compressed into half its volume, we have 

 « = 8 atmospheres. If again (8 feet = 96 inches) ^=16 

 atmospheres. And lastly V = 32 atmospheres, which is the 

 density at which the Portable Gas Company engage to supply 

 their friends. In the annexed figure is represented my own 



gauge 



