[ 230 ] 



XXVIII. On the Production of Electrical Phenomena by the 

 Rontgen Rays. By Aug. Righi*. 



1. XT is known that the most important properties of the 

 -H- X-rays, that is to say the power of exciting fluor- 

 escence and of acting on photographic preparations (which 

 Rontgen thinks is a secondary effect of the former), belong 

 more especially to the more refrangible of the ordinary rays. 

 Since these, in like manner, are eminently suited to produce 

 photo- electrical properties, I was desirous of examining 

 whether phenomena of this kind would also be produced by 

 the X-rays. 



As my investigation, though only recently begun, has 

 already given results, I will communicate them to the 

 Academy. For the sake of clearness it is necessary to give 

 a brief account of photo-electric phenomena. 



2. A body negatively electrified rapidly loses its charge if 

 exposed to radiations. The rapidity with which the charge 

 is dispersed is greater or less according to the nature of the 

 body and the wave-length of the radiations used. So that, 

 while for most bodies the phenomenon is produced only by 

 the rays of smallest wave-length emitted by the voltaic arc 

 (and especially by that produced between carbon and zinc or 

 aluminium), or by that of burning magnesium, for some 

 bodies, like amalgamated zinc, the sun's light is sufficient, 

 and for others, like the alkaline metals, the ordinary artificial 

 lights. 



I ought more especially to mention here an experimental 

 arrangement, that of the photo-electric couple f. The active 

 radiations fall on a metal disk after passing through wire 

 gauze parallel and close to it, and in connexion with the 

 earth. The radiations dispersing the negative charge which, 

 owing to the difference of potential by contact, the gauze or 

 the disk possesses (they having been placed in contact just 

 before the experiment) produce a deflexion, positive or 

 negative according to circumstances, in an electrometer in 

 connexion with the disk : this deflexion measures sensibly 

 the difference of potential in question J. 



If, in repeating the experiment, the disk is put further and 



* Rendiconti delV Accademia di Bologna, February 9, 1896. From a 

 separate copy communicated by the Author. 



t Mem. della R. Ace. di Bologna, series 4, vol. xiv. p. 369 ; Nuovo 

 Cimento, 1889, vol. xxv. p. 20. 



% Ibid, page 351. 



