Production of Electrical Phenomena by Rontgen Rays. 231 



further away from the gauze, the deflexion increases in ab- 

 solute value if it is positive, and diminishes to zero, or is 

 reversed, if it is negative. 



The direct cause of this is a phenomenon brought out from 

 my earliest researches on the electrical phenomena of radia- 

 tions: namely, that a discharged body becomes positively 

 charged when it is struck by radiations *. 



The above phenomenon is expressed by a law which I have 

 established by many experiments, and which can be thus 

 enunciated : the positive charge of the body on which the 

 radiations fall ceases to increase when the electrical density has 

 attained a certain value, which is constant for a given substance. 



It follows from this law, that the positive deflexion produced 

 by the radiations becomes smaller if the conductor in con- 

 nexion with the earth is brought gradually nearer the body 

 on which the radiations fall, the capacity of which is thereby 

 increased. Hence to show the positive charge produced by 

 radiations, the body on which they fall should not be too near 

 the uninsulated conductor. In the opposite case, which is 

 that of photo-electric couples, the formation of this final 

 positive charge has almost no influence on the deflexions 

 obtained. 



3. In order to examine whether the X-rays disperse the 

 charge of a body electrified negatively, and charge positively an 

 uncharged body, I worked with methods similar to those now 

 described : — 



(1) I charged a conductor in any given way, and then 

 examined whether its potential, as shown by a quadrant- 

 electrometer in connexion with it, underwent a more rapid 

 diminution than that arising from the usual dispersion of the 

 electric charge when the X-rays fall on it ; or 



(2) I caused the X-rays to fall on a photo-electric couple and 

 observed whether they produced a deflexion in the electro- 

 meter communicating with the disk, the gauze being put to 

 earth ; lastly, 



(3) I tried whether those rays falling on an uncharged body 

 produce a positive charge. 



In combining the most convenient experimental arrange- 

 ments, it was necessary to do so in such a manner that there 

 could be no possibility of any kind of electrical action being 

 produced directly on the electrometer, or on bodies in con- 

 nexion with it, by the apparatus generating the X-rays. 



I therefore arranged the Crookes' tubes, together with the 

 coil, the contact-breaker, &c, inside a large metal box in con- 



* Ibid, page 387 ; Nuovo Cimento, vol, xxv. p. 128 (1889). 



