ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
85 
was fixed to the bottom plate, the other could be adjusted to any distance from it by 
a rod sliding through a stuffing-box in the glass cover. The foot of the stand was 
insulated by a disc of ebonite, on which it stands. One such bell-jar is represented 
in fig. 79. It is 9^ inches (23'4 centims.) high and 5f- inches (14 - 9 centims.) in 
diameter; its cubical content, obtained by covering the open ends with glass plates 
and filling with water from a graduated measure, was found to be 3787 cubic 
centims. This jar was destroyed in the course of the experiments, and was replaced 
by others. In the figure an inner tube is shown with a series of holes in it, which 
was not used on this occasion, but will be spoken of hereafter. 
A remarkable phenomenon was observed on making connexion between the 
terminals and the battery by means of the discharging key, fig. 80 (already described 
in Part I., page 58), namely, that within certain limits of pressure in the bell-jar a 
sudden expansion of the gas took place, and that as soon as the connexion was 
broken the gas then as suddenly resumed almost exactly its original volume, showing 
only a small increase due to a slight elevation of temperature. The effect was similar 
to that which would have been produced if an empty bladder suspended between the 
terminals had been suddenly inflated and as suddenly emptied.'* We communicated 
this observation unofficially to our friend Professor Stokes in October, 1878. 
This phenomenon was quite unexpected, and being difficult to account for, was 
made the object of special study by means of an arrangement of apparatus as shown in 
fig. 81 . 
The glass cover of the bell-jar is furnished with a stop-cock which communicates 
with a gas-holder, and in the bottom plate there is a T-tube connected to two other 
stop-cocks, one of which communicates with the pumps, the other with a gauge about 
3 feet high. The right hand limb of the gauge dips into a rectangular glass cistern, 
the front face of which is polished to facilitate the reading; this limb is graduated 
from a zero well below the level of the mercury in the cistern, so that the height 
* This was first noticed by my former assistant, Mr. Seatox. 
