164 ROYAL SOCIETY OF CANADA 
enunciated by Paschen for discharges at high pressures, but also demon- 
strate beyond doubt the applicability of the same law to the critical 
pressure and to all pressures below it. 
The existence of the same relation has been sought in each of 
the gases, air, hydrogen, and carbon dioxide, and the result of the 
investigation has been the establishment with equal certainty of the 
same general law for all pressures, viz., that with a given potential 
difference, the field being uniform, the product of the pressure at 
which discharge occurs, and the distance between the electrodes, is 
constant. 
II. DESCRIPTION OF APPARATUS. 
The form of the discharge chamber is shown in Fig. I. 
The electrodes consisted of two plane brass plates a, a, 3-6 em. 
in diameter, embedded in ebonite as shown in the figure, the outer 


D Llechomek ToBattery 




RÉ 
À, 
> 
faces of the electrodes being flush with the surface of the ebonite. 
These pieces of ebonite which carried the electrodes served also to 
close the glass tube 7’, 7’, which thus constituted a discharge chamber. 
In order to confine the gas in this chamber to the region where the 
electric field was uniform, a ring of ebonite C, C, which projected over 
the edges of the brass plates, was inserted. In the construction of 
the apparatus special precautions were taken to insure that the plugs 
B, B, pressed tightly against the ebonite ring. As a result of this 
device, that portion of the electric field which was not uniform was 
