233 



Sir J. J. Thomson on the 



in the paper mentioned above, and are plotted in the diagram. 

 It will be seen that the ratio changes very rapidly with the 

 atomic weight when it is small, but it gradually becomes 





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constant for atoms of high atomic weight. The relative dis- 

 tribution of the secondary radiation round an atom thus 

 gradually becomes constant as its atomic weight increases, 

 and this we have seen is most likely to be the case if the 

 atom is spherical or approximately spherical in shape. 

 Cambridge, April 23, 1910. 



XVII. On the Theory of Radiation. By Sir J. J. Thomson, 

 M.A., F.R.S., Cavendish Professor of Experimental Physics, 

 Cambridge *. 



IN the Philosophical Magazine for August 1907, I discussed 

 a theory of radiation from hot bodies which regarded the 

 radiation as arising from the impact of negatively charged 

 corpuscles with the molecules of the body; the impact starting 

 * Communicated by the Author. 



