Metals subjected to Rontgen Radiation. 719" 



of themselves during the three hours or so of the experiment. 

 Consequently the fatigue must be due to a modification in 

 these films by the Rontgen rays. We do know that the contact 

 potential of the metal changes during exposure to ultra-violet 

 light and, presumably also, to Rontgen rays, and this change 

 of potential is best explained as a modification of an electrified 

 double-layer which has formed on the surface ; but we have 

 no evidence that the rays increase the density and absorbing- 

 power of condensed gas-films. The fact that freshly polished 

 plates increased in radiating power for an hour or so, points 

 even more strongly to the above conclusion. The effect of 

 polishing is undoubtedly to remove, at least partially, such 

 double-layers and gas-films. During the first part of the 

 experiment the films are forming and the radiation increases. 

 The formation of an electrified double-layer may easily have 

 such an effect, but it is extremely difficult to see how the 

 absorptive power of a gas can diminish while it itself is 

 growing denser. After the maximum value is reached and 

 the radiation begins to decrease, we have the same conditions 

 discussed above. 



As these experiments are the first attempt to show the 

 fatigue of metals due to Rontgen rays, they can be compared 

 only to the similar action of ultra-violet light. Of the inves- 

 tigators of the latter effect, Lenard ascribes it to the formation 

 of electrified double-layers, and Buisson to an absorption of 

 the rays by occluded gas. Hallwachs, who finds these insuf- 

 ficient to account for all the phenomena, assigns the dominant 

 action to an abnormal absorptive power of ozone existing as 

 a thin film close to the metallic surface. He claims that even 

 so minute a quantity as 1/130,000 of one per cent, of ozone 

 in the air would fully account for the normal fatigue. 



In a general way, my results agree with these views. And 

 in particular I have observed at times an increased sensibility 

 to the radiation corresponding to what Hallwachs found for 

 certain freshly prepared plates previously kept in closed 

 vessels for a considerable time. It is rather surprising there 

 should be such an agreement. The ultra-violet radiation 

 consists entirely of easily absorbed rays, while the secondary 

 radiation excited by Rontgen rays contains not only cathode 

 rays but also a proportion of penetrating rays. The presence 

 of these latter tends to complicate the results, as they would 

 not be absorbed easily by surface-films of gas. Since Sagnac * 

 found that the secondary radiation emitted by a light substance, 

 such as aluminium, contains a large proportion of penetrating- 

 rays,, we should expect its radiation to be the most unvarying 

 * Sagnac, Ann. cte Chim. et de Phys. xxii. p. 493 (1901). 



