210 Mr. G. A. iSchott on the Explanation of 



11. Results. — The results of this investigation may be 

 summarized as follows :— 



1. The 'photo-electric discharge from metals is a phenomenon 

 which, like radio-activity, is completely independent of tempe- 

 rature. The escaping electrons are therefore not the free 

 electrons of the metal, but are rather electrons which become 

 detached from the atom because of the coincidence of their 

 own natural periods with the periods of the impressed sether- 

 vvaves. 



2. The positive potentials acquired by different metals under 

 the influence of idtra-violet light are wholly independent of 

 temperature, and hence temperature changes produce no change 

 in the velocity of the electron within the atom, a result which is 

 in accord with the known thermal properties of monatomic 

 gases. 



3. The order in which metals in a vacuum exhibit photo- 

 electric sensitiveness bears no relation 'whatever to the Volta 

 contact series. The relation between this series and the order 

 in which the metals exhibit photo-electric sensitiveness in air 

 is probably due to the masking of the true photo-electric 

 effect by the effect of the double-layer formed between the 

 oxygen and the metal. 



4. The order in which the metals arrange themselves with 

 respect to the positive potentials assumed in a vacuum under the 

 injiue7ice of ultra-violet light bears no relation to the Volta 

 contact series. 



5. Clean unpolished metals exhibit in a vacuum, under the 

 influence of a given source, perfectly definite and constant 

 discharge rates. If fatigue effects occur at all, the recovery 

 from them is complete in the course of a few minutes. 



University of Chicago, 

 Nov. 29th, 1906. 



XIII. Note on the Explanation of the Radioactivity of Radium. 

 ■ By Gr. A. Schott, B.A., B.Sc, University College of Wales, 

 Aberystwyth *. 



"E may conveniently divide theories of radioactivity 

 into two classes : (1) theories which assume the 

 positive charge of the atom to be at rest, while the negative 

 charges are also at rest (theories of Lord Kelvin), or are 

 in motion (theories of Nagaoka and of J. J. Thomson);. 

 (2) theories which assume both positive and negative charges 

 to be in motion with large velocities. Theories of the first 

 class ascribe the energy of a and /3 particles to potential 

 energy stored in the atom, at any rate for the greater part ; 



* Communicated by the Author. 



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