﻿216 Mr. L. Yegard on the Properties of 



the upper strata of the atmosphere. This interpretation is 

 also in agreement with the fact that the streamers show a 

 radiation point. We further notice that the straight-lined 

 structure continues till the luminosity suddenly stops, forming 

 a sharp edge of the drapery band. 



In order to explain these straight-lined streamers, we must 

 suppose that the solar radiation producing them shows a very 

 small scattering, and we at once recognize one of the pro- 

 perties of a- rays. On the other hand, if the draperies are 

 at all formed as the effect of radiation penetrating down the 

 atmosphere, it is impossible to explain their structure by 

 assuming a radiation of the /3-ray type. 



As shown by Crowther *, the /5-rays are scattered at a 

 rate which is enormously greater than the rate at which 

 they are absorbed. Thus the /3-radiation would be spread 

 out in all directions as soon as it entered into the atmosphere, 

 long before it was absorbed in any appreciable amount. 

 Consequently , the luminosity produced would broaden out 

 and become diffuse, and ice should get no definite straight- 

 lined streamers. 



The small scattering of the solar rays, and the impossibility 

 of explaining the draperies by /3-rays, is also evident from 

 the extremely small thickness of the drapery bands. Adam 

 Poulsen, observing at Godthaab, has examined the bands 

 from the bottom edge in the direction of the streamers, and 

 he states that they appeared as if they had only linear dimen- 

 sions and no observable thickness. 



The suddenness with which the luminosity stops at the 

 end of the streamers shows that the solar rays quite suddenly 

 lose their power of producing luminosity. In other words, 

 if we were to observe the solar rays by the luminosity pro- 

 duced, we should find that they possessed a well-defined range 

 which in a striking way corresponds to the range of the 

 a-particles as found from the ionization produced in a gas. 



From the study of the discharge in ra rifled gases, we know 

 that places showing great luminosity correspond to places 

 where a great ionization takes place. The assumption is 

 then a very legitimate one, that the luminosity produced by an 

 a-particle along its path follows the same law as the ionization. 

 If so, the maximum intensity of light at the edge of the band is 

 simply explained if we suppose the ionization per unit length of 

 path of the solar rays to follow a law essentially similar to that 

 of a -rays (see fig. 1). 



On examining and interpreting the structure of certain 

 auroral forms, we have been able to show that the solar rays 



* J. A. Crowther. Proc. Roy. Soc. A. lxxx. p. 186 (1908). 



