904 On the Statistical Theory of Radiation. 



property of the air from waterfalls." Later on, we were not 

 able to reproduce this unexpected reappearance of new carriers 

 ((/. Aselmann, Ann. d.Phys. vol. xix. 1906), and this is quite 

 in agreement with Mr. Lonsdale's statement, that something 

 not yet known seems necessary to produce this result. 



I may perhaps also mention here one of our more recent 

 results bearing- on the subject (P. Lenard and C. Ramsauer, 

 Heidelberg Acad, of Sciences, 1910 ; also mentioned by 

 C. Ramsauer at the Rad. Congress at Brussels), namely, that 

 the smallest traces of water vapour, and perhaps also other 

 vapours, are of great influence on the size of the carriers 

 (ions) in gases — even at atmospheric pressure, — the carriers 

 becoming very large when traces of such vapours are present. 

 We have found this with carriers produced by ultra-violet 

 light. The usual drying of the air by phosphoric acid is not 

 >iitficient to reduce the carriers to their smallest size; they 

 became much smaller, if previous cooling to —70° C. was 

 employed to purify the air. It may therefore be expected, 

 that the large carriers from mercury-falls contain also many 

 molecules of the liquid (mercury). 



Physical Laboratory of the Yoiirs vei T sincerely, 



I'niversitv, Heidelberg, P. LENARD. 



Sept. 26, 1910. 



OIL On the Statistical Theory of Radiation. 

 To the Editors of the Philosophical Magazine. 



^ McGill University, Montreal, 



GENTLEMEN,— Sept> 6? ly]() 



IX the Philosophical Magazine for August (p. 350) 

 Sir J. Larmor gives reasons for supposing that my 

 conclusion, that his modification of Planck's theory of 

 natural radiation does not evade the main difficulty that an 

 atomic constitution of radiation must be implied, need not 

 follow. 



Sir J. Larmor states that on his theory k need not be 

 equal to the gas constant for one molecule but is indeterminate. 

 To make this clear it ought to be shown that the calculations 

 of k given by Boltzmann, Planck, and others can be modified 

 so as to leave k indeterminate. This I think has not yet 

 been done, and until it has been done the conclusion that k 

 must have a definite value cannot be regarded as disposed of. 

 The only reason why Planck w r as obliged to introduce the 

 idea of finite elements of energy was that he found the only 

 possible value of k to be that of the gas constant for one 

 molecule. Yours very truly, 



Harold A. Wilson. 



