The passage of homogeneous Röntgen rays through gases

The phenomena attending the passage of Röntgen rays through gases has been examined by several experimenters. The relative ionisation produced in different gases was investigated early in the history of Röntgen rays by Perrin and Rutherford, and later by Sir J. J. Thomson, Strutt, McClung, Eve, Barkla, and Crowther. Some of these experimenters allowed the rays to strike the electrodes and the walls of the ionisation chambers; this gave rise to corpuscular radiation which was totally absorbed in ths gas, so that the ionisation observed was higher than the true value, and consequently the apparent relative ionisation was smaller than it should be for those gases in which the ionisation is greater than in air. Sir J. J. Thomson, McClung, and Crowther took precautions against this source of error, but in every case rays direct from a Röntgen bulb were used, and these rays were necessarily heterogeneous, and the heterogeneity was different in the various bulb. In experiments on the relative location in gases by Röntgen rays, not only rays of exactly the same hardness and the same intensitv should be used to ionise each gas, but in order to obtain quite definite results it is necessary to use rays of a distinct hardness. Barkla's discovery of homogeneous rays emitted by different metals when Röntgen rays fall upon them makes it possible to use rays of a definite hardness. Such homogeneous rays have been used by Barkla to investigate the amount of ionisation relative to air produced in different gases and vapours. The main object of the following research is to investigate more fully the various phenomena observed when homogeneous rays pass through gases composed of elements in the group in which no appreciable homogeneous radiation has been detected for rays of penetrating power within the range of that of those homogeneous beams emitted by metals of atomic weight from iron to silver. The gases used are air, carbon dioxide, and sulphur dioxide. The investigation may be divided into three parts— (1) The absorption of homogeneous rays.