8 G 
MESSRS. W. DE LA RUE AND H. W. MULLER OH THE 
of the column of mercury may be determined with facility. P and N are screw 
terminals connected with the battery. 
The following experiment in rarefied air will give an idea of the amount of 
instantaneous expansion which occurs when the terminals are connected with the 
poles of the battery. 
Pressure, 
m.in. M. 
Distance of the terminals, 6 inches, the top one a point, 
the lower a disc. 56 73,684 
On making contact the arc passed and the column of 
mercury was depressed . 15'8 20,789 
Pressure on connexion. 71'8 = 94,473 
11,000 cells, current 0‘01102 W; the resistance of the bell-jar was reproduced 
by substituting 600,000 ohms wire resistance. 
The volume of the bell-jar is 3787 cub. centiins., the temperature at the time of the 
