﻿234 Mr. L. Vegard on the Properties oj 



that the line 5570 was due to fluorescent or phosphorescent 

 light. Later on, A. Schuster * called attention to the fact 

 that this auroral line very nearly coincides with one of the 

 krypton lines (\= 55704) . According to Kayser, however, 

 this coincidence does not prove identity of the two lines ; 

 for the auroral spectrum does not give the other krypton 

 lines with the intensity to be expected from the ordinary 

 krypton spectra. 



The difficulty in interpreting the auroral spectrum indicates 

 that the spectrum depends essentially on the peculiar way in 

 which it is produced. 



According to the view put forward in this paper, the light 

 is produced by an electric radiation of the a-ray type pene- 

 trating down the upper strata of the atmosphere. At present 

 we do not know very much with regard to the nature of the 

 light produced in this way. 



The spontaneous luminosity given out from RaBr 2 has 

 been examined by Sir William and Lady Huggins j-. They 

 found the part of the spectrum examined to be essentially 

 similar to the negative band spectrum of nitrogen, and besides 

 they found a band (about \ = 5165) the origin of which they 

 were unable to explain. From the fatigue effect produced 

 by hydrogen they concluded that the /3-rays did not greatly 

 contribute to the luminosity, which they supposed to be 

 given out from the region inside the solid substance. 



B. Walter J was the first to show that light was also given 

 out from the air surrounding the radioactive substance. He 

 experimented on polonium and found a spectrum similar to 

 that of radium bromide : but in the case of polonium it more 

 resembled the positive band spectrum of nitrogen. 



II. Pohl§, F. Himstedt and G. Meyer ||, showed that, also 

 in the case of radium bromide, the surrounding air gave out 

 a faint luminosity which could be detected photographically. 

 R. Pohl states that luminosity in the air can be observed 

 several centimetres from the substance. 



As polonium only gives out a-ray s and the very absorbable 

 S-rays which do not ionize, the luminosity given out from 

 the air several centimetres from the substance must be 

 produced by a-rays. 



When we are going to make comparison with the auroral 



* A. Schuster, ' Nature,' No. 58, p. 151 (1898). 



t Sir William and Lady Hugg-ins, Proc. liov. Soc. lxxii. pp. 198 and 

 409 (1903) ; lxxvi. p. 488 (1905). 



t B. Walter, Ann. d. Physik, xvii. p. 367 (1905); xx. p. 327 (1906). 



§ R. Pohl, Verh. d. D. Phys. Ges. vii. p. 458 (1900). 



|| F. Himstedt and G. Meyer. Ber. d. naturf. Ges. zu Freiburg in Br. 

 xvi. p. 13 (1905). 



