[carr] AN EXTENSION OF PASCHEN’S LAW 167 
phoric pentoxide. The discharge chamber was then exhausted to 
about 20 mm. of mercury and allowed to stand at this pressure for a 
period of from eight to twelve hours. 
During this time the air was always in contact with phosphoric 
pentoxide in the drying tube, and was, therefore, entirely free from 
moisture when the measurements were taken. 
The first measurements were made with the electrodes 3 mm. 
apart, and the spark potentials were determined over a range of 
pressures extending from 51 mm. down to :35 mm. of mercury. The 
Fig. ~ Arr 












C 



FPofen/iol Life E72? LOS 










2 5} FA 
Fressure in Millimelres Of ME CULy 
spark potentials corresponding to the various pressures are recorded 
in columns 5 and G of Table I., and the results are represented graph- 
ically in Fig. IL, a. 
In making these determinations the precaution was always taken 
of allowing eight or ten minutes to intervene between consecutive 
readings in order to make certain that the air was in its normal con- 
dition when the discharge occurred. As can be seen from the figure 
the curve is quite regular and exhibits all the peculiarities already 
noted by Peace,’ Strutt,? and Bouty®. The curve, however, is carried 
much higher than those drawn by any of these experimenters, dis- 
charges corresponding to potential differences of over eighteen hun- 
dred volts being recorded. 


1 Peace, Roy. Soc. Proc., Vol. 52, p. 111. 
3 Strutt, Phil. Trans., Vol. 193, p. 384. 
5 Bouty, Comp. Rend., Vol. 131 (2), p. 446. 
