348 Prof. Ch. V. Zenger on a New Steam-gauge. 



the capacities so that the first is filled when the pressure in- 

 creases by two atmospheres, the second when it increases by four, 

 and so on. In this way three tubes suffice for a manometer that 

 is to show pressures up to 6 atmospheres, four tubes for one 

 that is to go up to 8 atmospheres, and so on. In this case the 

 capacities of the separate tubes are given by formulae of the same 

 kind as before — namely, for a manometer to be used up to 6 

 atmospheres : — 



v L + V2 + v 3 +v 4 = l s 



'2 + ^3 + ^4 = 



1 



M- v 4= 



1 



v 4 = 



i 



7* 



v x = 



: 3" = 



= T7s' 



v 2 = 



2 

 : 15 = 



2 

 = 3T5' 



v 3 = 



2 

 35 = 



2 



v 4 = 



1 



7' 





To prevent the accidental breakage of the manometer, it is 

 fastened to the graduated brass plate, and with it screwed to a 

 glass cover, J of an inch thick, capable of supporting a pressure 

 of 20 atmospheres. The glass cover is pressed by a screw at 

 the top upon a plate of india-rubber, thus entirely preventing the 

 entranee of dust or damp. 



The apparatus has already been at work for eighteen months 

 in several manufactories in Austria; and it has been found, by 

 comparative experiments with it on the Northern and State rail- 

 ways of Austria, that it is steadier and more accurate than the 

 standard spring and piston manometers used by the companies 

 for graduating their own manometers. Two of these instru- 

 ments were placed side by side on the same steam-boiler, with 

 a new spring manometer by MM. Bendenberg and Schaffer, of 

 Magdebourg ; but up to the time of my leaving Prague (that is 

 to say, during 1^ year) they remained in strict accordance all the 

 time, not \ pound difference of pressure being indicated by 

 them, although the temperature of the engine-room varied 

 greatly, and one of the air steam-gauges was placed directly on 

 the boiler (on direct steam), and quite near the fire, where the 

 temperature reached 30° or 35° C. 



The elasticity of air not being subject to alterations like the 

 elasticity of a spring, which is greatly affected by heat and by 

 rapid variations of pressure, the new gauge is more steady and 

 requires less attention than spring gauges of any kind. It also 

 possesses a still greater advantage in being much more sensible 

 to small changes of pressure, and indicating them instanta- 



