1896.] 



on Electric Shadows and Luminescence. 



201 



beautiful " inductoscript " photographs. Upon the screen I throw a 

 few samples, including a print of one of the jubilee coins (Fig. 4). 

 These curious photographs are pro- 

 duced simply by the chemical ac- 

 tion of the electric discharges 

 which stream off from all the pro- 

 jecting portions, and so roughly 

 reproduce an image of the coin. 

 Since Roentgen's discovery many 

 persons have announced their sup- 

 posed discovery of the production 

 of electric shadow-pictures without 

 the aid of a Crookes tube. What 

 they have really observed is, how- 

 ever, totally different. They have 

 not been producing X-rays at all, 

 but have merely rediscovered these Fig. 4. 



inductoscript shadows. 



Between the researches of Crookes, however, and those of 

 Roentgen there came in a very remarkable body of researches in 

 Germany. I have but to name Goldstein,* Puluj, f Hertz, J 



* Goldstein, in his researches on the Keflection of Electric (i.e. Kathode) 

 Eays in ' Wiedemann's Annalen,' xv. 246, 1882, came very near to the discovery 

 of the Roentgen rays. After pointing out that Hittorf had held the opinion 

 that the kathode rays end at the place where they strike upon a solid wall, and 

 that they are unable to proceed in any direction at all from thence, Goldstein 

 directs attention to the circumstance that fluorescent patches are sometimes seen 

 at the end of crooked tubes, where they could not have been caused by the 

 direct impact of kathode discharges. He discusses the question whether this 

 is due to reflection or to a deflection caused by the spot where impact first took 

 place having become electrified negatively, and therefore acting as a secondary 

 kathode. The latter hypothesis is rendered untenable by his observation that 

 if the spot of first impact is made an anode the effect still occurs. He then 

 shows that the phenomena are inconsistent with a specular reflection, but are 

 explained by supposing that there is a diffuse reflection. He then sums up as 

 follows : — " A bundle of katliode rays does not end, at least under those circum- 

 stances under which it excites phosphorescence, at the place where it strikes 

 upon a solid wall, but from the place of impact on the wall there proceed electric 

 rays in every direction in the gaseous space. These rays may be considered as 

 reflected. Any solid wall of any property whatever may serve as a reflecting 

 surface. It is immaterial whether or not it is capable of phosphorescence, or 

 whether it consists of an insulator or of a conductor. The reflection is diffuse, no 

 matter whether the surface is dull or most highly polished. An anode reflects 

 the kathode rays sensibly as well as a neutral conductor or an insulator. The 

 reflected rays have, like the direct kathode rays, the property to excite phos- 

 phorescence at their ends. They are subject to deflection, and their ends are 

 deviated in the same sense as the ends of kathode rays, which would extend 

 from the reflecting surface toward the place hit by the reflected rays." 



t Puluj, " Radiant Electrode Matter and the so-called Fourth State." Pub- 

 lished in vol. i. of ' Physical Memoirs,' by the Physical Society of London, 1889. 

 These are translated from papers published in 1883 in the Memoirs of the Imperial 

 Academy of Sciences of Vienna. 



X H. Hertz. Researches on the Glow-Discharge, Wied. Ann. six. 782, 1883. 

 Hertz regards the kathode rays as a property of tlie ether, not as consisting ol 



