Page:Proceedings of the Royal Society of London Vol 69.djvu/297

It will be noticed that except at the higher pressures the leak is proportional to the pressure. The falling off from this law at the higher pressures might be taken as indicating that the ionisation is due to radiation from the walls of only moderate penetrating power; it is possible, however, that at the higher pressures a sensible proportion of the ions recombine, so that the current is not a measure of the ionisation. There can be no doubt that, for the range of pressures for which the leakage is proportional to the pressure, we may consider that the saturation current was attained, and the rate of leak may be taken as a measure of the ionisation. It is for such pressures that the relative ionisations have been calculated. They are collected together in the table which follows.

Gas.	Relative ionisation.	Relative ionisation./Specific gravity.
Air	1·00	1·00
${\ce {H2}}$	0·184	2.7
${\ce {CO2}}$	1·69	1·10
${\ce {SO2}}$	2·64	1·21
${\ce {ChCl3}}$	4·7	1·09

If we except hydrogen, the ionisation is seen to be very nearly proportional to the density of the gas. The deviations in the case of the other gases in fact hardly exceed what might be attributed to experimental errors, for variations amounting to as much as 10 per cent. occurred in the determination of the rate of leak for a given gas. The departure from the law in the case of hydrogen cannot be attributed to experimental error, nor is it due to want of purity of the gas, as is shown by the agreement in the results obtained with the gas prepared by different methods.

The results obtained for the relative ionisation occurring spontaneously in all the gases tried, including hydrogen, show a remarkable similarity to those obtained by Strutt^[1] in the case of the same gases when under the action of the Becquerel rays, as the following table shows (p. 282).

It was pointed out by Strutt that the conductivity under the action of the rays is nearly proportional to the density of the gas, hydrogen, however, being an exception. As will be seen, the results I have obtained for the spontaneous ionisation agree more nearly with those obtained by Strutt for gases exposed to radium radiation than for the same gases under the action of polonium rays.

An account of measurements of the loss of electricity from a charged conductor suspended in a closed vessel containing various

1. 'Phil. Trans.,' A, vol. 196, pp. 507-527.