166 ROYAL SOCIETY OF CANADA 
electrode. This procedure was followed until a potential sufficiently 
high was reached to break down the gas and cause a discharge. The 
passage of the discharge could be readily noted as it was accompanied 
by a violent deflection of the electrometer needle. 
The well known phenomenon of delay in the passing of the 
discharge, which has been investigated at length by Warburg,’ was 
observed throughout the experiments. It was especially marked in 
FIG. /l@) 
/800 
| 
1600 Re a 


S 
S 
TE 
= 
: 


8 
| 
\ 
À 




Polertial Difterence in lols 

eat 
À 
À 
ia 
| 







3 
200 
2 
/ 15 
6 9 
Pressure in Millimelres 
the neighbourhood of the critical pressure, discharges being frequently 
obtained ten or even fifteen minutes after the requisite voltage had 
been applied. 
In every case, therefore, as the minimum sparking potential for 
any pressure was approached, a considerable time was allowed to 
elapse, with a given applied potential difference, before any increase © 
was made. 
III. EXPERIMENTS IN AIR. 
In the experiments on atmospheric air the whole discharge 
apparatus was first exhausted to a very low pressure and then refilled 
by fresh air, which bubbled in very slowly, first through a wash-bottle 
of sulphuric acid and then through a tube tightly packed with phos- 

1 Warburg, Ann. d. Phys., Vol. 62, p. 385. 
