144 Mr Whiddington, Note on the Rontgen radiation 
relate RRS 
Note on the Rontgen radiation from cathode particles tra- — 
versing a gas. By R. Wurppineron, M.A., St John’s College. 
[Head 11 November 1912.] 
IT is now a commonplace that Rontgen rays are emitted from 
a target struck by cathode particles, and very many researches 
have been carried out with the object of determining how the 
nature of the target and the velocity of the incident particles 
determine the quantity and the quality of the emitted Rontgen 
rays. The experiments shortly to be described bring forward 
evidence to show that when very slow cathode particles traverse 
a gas at low pressure, Roéntgen rays are emitted all along their 
ath*. 
: The form of apparatus used is indicated in the figure. <A hot 
lime cathode L projects a fine beam of cathode particles down the 
axis of the evacuated glass tube 7, the anode being a spiral of 
aluminium wire A. An insulated aluminium plate P is enclosed 
in an earthed brass tube Z, provided with a small opening at W. 
This opening is closed by a thin blown-glass window, so thin as to 
show interference colours of a low order. P is connected to the 
leaf of a Wilson tilted electroscope. The arrangement of taps 
shown in the diagram enables connection between 7’ and # to be 
severed after a moderate vacuum has been produced so that a 
slightly higher vacuum may prevail in # than im 7. This is 
desirable since we wish to observe the potential to which P will 
rise, and it is necessary under such circumstances to eliminate any 
gas leak due to ionisation. 
In the earlier experiments it was found that when the 
cathode stream from JL was passing down the tube there was 
an enormously rapid deflection of the gold leaf in such a direc- 
tion as to show that the plate P was charging up positively. 
This effect was finally traced to defects in the window W, small 
cracks being present which apparently allowed a diversion of the 
main current into the brass cylinder, P functioning as a subsidiary 
anode and becoming positively charged. When the window, how- 
ever, was apparently perfect there was still an. effect in the same 
direction, the plate P charging up positively as before but at 
a very much diminished rate. A strong magnetic field applied 
across W had little or no effect upon the rate of charging of P. 
Moreover, when the narrow pencil of rays from LZ was curled up into 
a close spiral in front of the window, but not touching it, P charged 
* No rays can be detected unless the applied potential exceeds 90 volts. 
