Metals subjected to JRontgen Radiation. 709 



of a metallic surface and of the condition of adherent gaseous 

 layers, that it is natural to expect discrepancies where these 

 are controlling factors. 



As a summary of the work is given in Professor Thomson's 

 6 Conduction of Electricity through Gases,' page 289, it is 

 necessary only to supplement this by reference to what has 

 appeared since. Ramsay and Spencer * haye attempted to 

 prove that this fatigue is conditioned by the disintegration of 

 the metallic atoms. Allen f has solved one difficulty by 

 proving that fatigue occurs in a good vacuum, and has added 

 the new and important fact that the fatigue of zinc can be 

 expressed as a sum of two exponential terms. He also shows 

 that the longer waves possess the property of producing a 

 partial recovery in the activity, the exponential decay having 

 been obtainable only when they were absorbed. It is to be 

 hoped he will continue the work to include the details of 

 this important property. In addition to this new matter, 

 Hallwachs % has continued his researches and published 

 them in an elaborate and comprehensive paper. In the 

 first part he considers the various hypotheses in detail, 

 and apparently on good evidence rejects the conclusions of 

 Ladenburg § that the fatigue is caused by oxidation or 

 corrosion of the metal, and proves, contrary to Buisson || and 

 Kreusler %, that darkness does not prevent fatigue. In the 

 second part of the paper he investigates the cause of the 

 effect. Here he confirms the theories of Lenard** and 

 Buisson, that the fatigue is due in part to absorption of the 

 radiation from the metal by electrified double-layers and 

 films of gas on the surface, modified in some way by the 

 ultra-violet light. But he assigns the dominant influence to 

 the presence of ozone in these absorption-layers. However,. 

 it has yet to be proved that minute quantities of ozone possess 

 such an abnormally large absorptive power on the cathode 

 rays issuing from the metal. He also shows that the 

 activity may increase to a maximum value before fatigue 

 begins. 



As Rontgen rays excite a secondary radiation in metals 

 we may expect to find, in this case, effects of fatigue ; and 

 the experiments described in this paper prove that this typo 



* Ramsay and Spencer, Phil. Mair. xii. 1906, p. 397. 

 t H. S. Allen, Proc. Roy. Soc. A', lxxviii. 1907, p. 483. 

 X Hallwachs, Sitzunysber. der Ges. der Wissensch. zu Leipzig, lviii'. 

 190(5, p. 341. 



§ Ladenburg, Annal. der Phys. xii. 1903, p. 558. 

 || Buisson, Ann. de Chim. et de Phys. xxiv. 1901, p. 320. 

 If Kreusler, Annal der Phys. vi; 1901, p. 398. 

 ** Lenard, Annal. der Phys. viii. 1902, p. 196 ; xii. 1903, p. 490. 



