180 ROYAL SOCIETY OF CANADA 



Ava*; removed. With the galvanometer which we used, a light of one 

 •candle power at a distance of one metre was found to give a defection of 

 thirty scale divisions. The deflections were so consistent that the cell 

 would have made a very fair photometer. The battery used was a single 

 ■cell of a silver chloride testing batter}', and the variations of resistance 

 were observed by the bridge method using the slide box and wire 

 megohm. 



The same selenium cell was exposed at a distance of three inches 

 from the tube to the most powerful X-radiation which we could ])roduce, 

 but no elfect whatever could be observed. The sensitiveness to light was 

 tested both before and after exposure several times, but no change could 

 be detected. It may be necessary to remark that the selenium was pro- 

 tected from the light and from the electric discharge by a double thickness 

 of one-mil aluminum foil, which though absolutely opaque to light, did 

 not cast a perceptible shadow on the fluoroscope when tested by the X^^ 

 rays. The screen of foil was connected to earth and to one pole of the 

 galvanometei'. It is necessary to emphasise these precautions as it 

 appears that other observei's have obtained positive results by neglecting 

 them. The galvanometer which we used was adjusted to give a deflection 

 of 1 scale divi-sion for 1 volt through 50,000 megohms. It had a resis- 

 tance of 110,000 ohms, and a period of 15 seconds. 



E/eetrostatir effects of the X Rays. — Within a short time of the 

 publication of Rimtgen's discovery, it was shown by J. J. Thomson 

 that the X-rays possessed the same ])roperties as the kathode rays of 

 Lenard. of discharging an electroscope, however, carefully insulated. He 

 expressed this result b,y saying that any substance through which the X- 

 rays passed, was rendered for the time a partial conductor. The beha- 

 viour of paraffin wax in particular was given as an instance of this effect. 

 The time of discharge of an electroscope or of a small condenser has 

 been suggested as a means of measuring the intensity of the X-radiation 

 at various distances and under A'arious conditions. Some very surpris- 

 ingly exact proofs of the law of the inverse square were obtained in this 

 manner by some French physicists. 



It appeared from some of oui- photogra])hs, that the X-rays were not 

 dirt'u.sed from the platinum plate according to the same law as obtains in 

 the case of the difl'use reflection of ordinary light. We endeavoured to 

 use the discharge method for measuring the intensity of the rays dittused 

 in <liflerent directions. We found, however, that it was not possible to 

 operate the tube at a perfectly constant intensity, and the rate of dis- 

 charge itself did not appear to be alwaj'S uniform even if there were no 

 apparent chtinge in the tube. It thei-efore occurred to us to tr}^ whether 

 with a very sensitive galvanometer the leakage current itself might not 

 be directly observed. For this purpose we constructed small condensers 

 of very thin aluminium foil and paraffined paper. The foil was so thin 



