1923. No. lO. DISTRIBUTION OF MATTER IN THE ATMOSPHERE. I5 



From the point of view here taken with regard to the constitution of 

 the upper strata of the atmosphere, we might expect that the clusters would 

 accumulate near the plane of the magnetic equator, where this dust atmosphere 

 would reach a maximum height, and thus there might be formed a kind 

 of dust ring round the earth as indicated in Fig. 5. — This dust will scatter 

 the sun light and such a disc of small particles is just wanted to explain 

 the zodiacal light. — Long after sunset the sun will still illuminate this 

 dust ring and at places near the equator we see a cone of light rising up 

 from the horizon. If the disc reaches a height of the same order of 



Dust= Atmosphere 



Fi£ 



Sun 



magnitude as the diameter of the earth, we may see the luminosity on the 

 other side of the earth (opposite to the sun) in the form of what is called 

 "Gegenschein". (Fig. 6.1 



As this dust ring is composed of electrified particles in motion, it is 

 maintained through a continual process, and it is to be expected that the 

 dust ring may undergo certain variations, and the zodiacal light is not 

 always equally strong even at the same place and under the same light 

 conditions. It is even possible that fairly sudden changes may occur with 

 regard to the intensity and outlines of the zodiacal light. Indeed some 

 observers, e. g. von Humboldt and Rev. George Jones, state, that they 

 have noticed very marked changes in the intensity of the zodiacal lights. 



Although one of Birkeland's experiments is of interest as an analogy 

 to illustrate the wa}' in which matter is distributed in the upper strata of 

 the atmosphere, still the explanation here given for the zodiacal light is 

 essentially different from that of Birkeland. According to his view the 

 zodiacal light should be explained in a similar way as the northern 

 lights, viz. as a direct effect of radiation from the sun, only that the two 

 phenomena were produced by different groups of rays. 



The question now might naturaliy arise whether the ring of Saturn 

 might not be a system of electrical dust formed in a similar way as the 

 assumed dust ring round the earth? If so, it would follow that Saturn 



