was measured, most of them had become singly charged through drawing to themselves the singly charged negative ions with which they were mixed. This hypothesis found some justification in the fact that in the early experiments the mean value of
for the positive ions had indeed come out some 15 or 20 per cent higher than
—a discrepancy which had at first been regarded as attributable to experimental errors, and which in fact might well be attributed to such errors in view of the discordance between the observations on different gases.
Franck and Westphal,[58] however, in 1909 redetermined
by a slight modification of Townsend’s original method, measuring both
