MK. W. _n. CAEE ON THE LAWS GOVERNING 
40-j 
Since the statement of tliis law by Paschex, Peace^"" alone seems to have 
published results which could throw any additional light on the conditions holdino- 
lor discharge in a gas- at very low pressures. Peace experimented in air, with 
parallel plates as electrodes, at various distances apart, and found that the value of 
the critical j^ressure increased greatly as the distance between the electrodes was 
lessened, but his results at points below the critical pressure give no evidence of the 
existence of any such law as had been enunciated by Paschex. 
This can be readily seen from the numbers recorded in his paper, a tew of which, 
selected from readings taken below the critical pressure, are given in the following 
table. These results admit of easy comparison, since the potential ditferences in the 
cases chosen are very nearly the same. The product of pressure and spark length 
should be a constant quantity if Paschex’s law held. 
Table of Peace’s Eesults. 
i 
A])plied potential 
Pressures in 
Distance between 
Product of 
j difterence in 
inillims. 
electrodes in 
pressure and 
volts. 
of mercury. 
inches. 
spark length. 
6t9 
660 
' 2 , ■ 0 
6 
■082 
•005 
• 205 
•030 
670 
5 
•021 
■105 
731 
2-5 
•030 
•075 
It we compare the tirst and second of these results where the difference in spark 
potentials is only 11 volts, we find the product in the first case nearly seven times that 
in the second. Again, the product coi'respondiiig to the spark potential G60 volts is 
less than one-third that corresponding to 670 volts, a large difterence in the opjiosite 
direction. The same irregularity is exhiliited by the product corresponding to the 
spark potential / 31 volts, and it seems difficult to understand how experimental 
errors could be made to explain such a wide divergence of results. 
At the critical pressure Peace’s results point to the existence of the law, but, as 
stated above, it would appear that as soon as lov'er pressures were approached the 
indications were uniformly against the existence of the relation which Paschex found 
to hold at high pressures. 
Owing to the special precautions taken by Peace to obtain accurate values for the 
spark potentials, it is possible to arrive at but one of two conclusions regarding the 
departure from Paschex s law indicated by Peace’s numbers. Judging by the 
results, either the law ceases to hold when the critical pressure is passed, or else the 
apparatus used by him in his experiments did not admit of an accurate measurement 
of the actual spark lengths corresponding to different spark potentials. 
* Peace, ‘ Roy. Soc. Proe.,’ vol. 52, p. 99. 
