Charged Surface Layers in Contact Potential Phenomena. 24 B 



was found that if cathode rays were allowed to strike a very- 

 thin metallic anticathode, the intensity of the Rontgei* 

 radiation in a direction near that of the cathode beam was- 

 much greater then in the opposite direction, the ratio in the 

 case of an aluminium anticathode being sometimes as great 

 as 3*2, indicating a mean velocity of the radiating electrons- 

 of nearly *5. As Mr. Kaye does not say what the velocity of 

 his rays was, a direct comparison with the calculated velocity 

 is impossible ; but indeed it would be a very poor check om 

 the accuracy of the assumptions, for the opposing influences 

 of the retardations and deflexions of the cathode particle, that 

 diminish the effect, and the increase of its velocity on close 

 approach to a positive electron (the only kind that can cause 

 appreciable radiation), may produce great changes in the 

 velocity of an electron before it radiates. But the order of 

 magnitude of the effect, as well as an observed difference in 

 hardness of the rays, to be accounted for by the well-known 

 Doppler effect, does much to confirm this hypothesis. 



From these results it appears that the secondary cathode 

 particles, while they must produce some radiation, possibly a 

 part of Barkla's homogeneous secondary radiation, cannot 

 produce any distributed like the secondary radiation on which 

 Mr. Crowther's experiments were performed. And since the 

 results of his experiments, as well as those of Mr. Kaye, are 

 well accounted for by the theory of Rontgen rays as electro- 

 magnetic pulses, and are necessary consequences of this 

 theory, they are also important confirmations of its funda- 

 mental assumptions. 



Jefferson Physical Laboratory, 

 H arvard University . 



Nov. 2, 1912. 



XXIX. On the Charged Surface Layers in Contact Potential 

 Phenomena beticeen Metals. By A. Norman Shaw, M.Sc, 

 1851 Exhibition Scholar of McGill University, Montreal";. 

 Research Student of Gonville and Caius College, Cambridge*. 



THE presence of charged surface layers has been assumed 

 by many investigators on contact electromotive forces, not 

 only by those supporting the " chemical theory" of its nature, 

 but also by some of those who believe that the phenomenon 

 is an intrinsic property of the metals. The following ex- 

 periments were performed with the idea of obtaining some 



* Communicated by Sir J. J. Thomson, O.M., F.R.S. 



