with the Brush Discharge, 53 



be immediately discharged, and therefore when they subse- 

 quently impinged upon the plate no effect would be produced. 

 This was found not lo be the case, as is shown by PI. I. (fig. 3), 

 which was produced by employing a piece of tin for the 

 reflecting surface instead of glass. 



That the metal plate did receive the impact of electrified 

 particles was shown by the fact that sparks could be drawn 

 from it from time to time. 



In view of the statement of Tesla, that the efficiency of 

 the metals as regards their reflecting powers for #-rays 

 follows their order in the voltaic series, an attempt was made 

 to test if any variation of reflecting power could be detected 

 in the present case. For this purpose the metal reflecting- 

 plate was varied, but the experimental results show that no 

 conclusions can be drawn indicating any connexion between 

 the reflecting-power and position in the electrochemical series. 

 In fact the reflexion seems to depend upon the brightness of 

 the surface, and therefore agrees exactly with the reflexion 

 of light. 



7. Penetrative Effects produced by the Brush-Discharge. 



The remarkable results obtained by Hontgen and others 

 induced an attempt to imitate the effects by the brush-discharge. 

 For this purpose a sensitive plate was wrapped in brown 

 paper (two folds), and on the paper were placed sundry small 

 articles, such as coins, keys, &c, and the whole exposed to the 

 brush-discharge. The experiment was made in a darkened 

 room, and the point placed at about 5 to 6 centims. above the 

 coins, the plate lying on the table. An exposure of 30 minutes 

 was given, and on developing the plate the outline of the 

 articles was distinctly shown. This experiment was repeated 

 with brushes of different polarity and source {i. e. coil and 

 machine), and in every case the same results were obtained. 

 Probably the cause of this action is that the substances 

 become charged and act inductively upon the silver salt in the 

 sensitive film, causing a partial decomposition or production 

 of a " latent image/' which decomposition is carried still 

 further in the process of development of the plate. The next 

 step was to see if the outline of the bones could be produced 

 without the flesh. Numerous experiments were made, but 

 although in all cases the outline of the hand could be repro- 

 duced in no case did the bony skeleton show itself. 



None of these effects could be obtained when a piece of 

 vulcanized fibre was included in the wrapping. This substance 

 has been shown by Giffard and others to be impervious to 

 #-rays, and, of course, it is equally impervious to light. 



