622 BIRKK1.ANM). I UK NORWEGIAN Al'RORA POLARIS EXPEDITION, 1 QO2 -1903. 



The commencement of the sectional line, where by far the most of the rays cross each other, would 

 then from the centre of the terrella he seen with lengths of 192 and 185' respectively. These angles 

 must however he calculated along the magnetic equator of the terrella. 



If it he further remembered that all three sectional lines referred to, by stronger and stronger 

 magnetisation of the terrella, draw back somewhat, being pushed outwards almost parallelly with a quite 

 slight reduction in length, it will be evident that with so intense a magnetisation as to correspond with the 

 conditions on earth, the second sectional line would begin and be most strongly developed at a length 

 but a few degrees less than .180 reckoned on the magnetic equator. 



Returning now to the earth, supposed to be travelling in the ring of radiant matter round the sun 



At the equinoxes we shall see the places where the corpuscle rays are intersecting each other in 

 the "second line of precipitation" in a line with the ring of radiant matter in the sun's magnetic equator, 

 which ring must be assumed to continue also beyond the earth's orbit. 



In this manner we shall be able to see through the radiant matter into a considerably thicker stra- 

 tum opposite the sun, as shown diagramatically in fig. 225, and more light will be diffused, by reason of 

 which Gegenschein may be imagined to be caused. 



121. We now pass on to mention how the spectral analysis investigations which have been made 

 of these phenomena look in view of the theory advanced here. 



The spectrum of the zodiacal light has been observed for man} 1 years, but owing to its faintness 

 the observations are very difficult to make. Among the first observers were LIAIS('), YOGICL(-), PIA//I- 

 SMYTH l :l l, and WRIGHT | '). LIAIS at times suspected dark lines, but could not be certain of their exist- 

 ence. WRIOIIT detected the presence of the atmospheric band at }. 5780. Other observers had thought 

 the bright aurora line at /. 4571 a part of the zodiacal light spectrum, but the work of the last three of 

 the above-mentioned observers seems quite conclusively to show that this belongs to the aurora alone, 

 although it ma} 7 at times appear superimposed upon the spectrum of the zodiacal light. This fre- 

 quently occurs if the aurorse are at all common at the place of observation. HAI.L( : '), observatory in 

 Jamaica, found the spectrum continuous even when using a slit sufficiently narrow to show absorption 

 lines in the spectrum of daylight. In other respects, all observers agree in finding the spectrum conti- 

 nuous with an intensity curve quite similar to that of daylight. 



The fact that the intensity curve of this spectrum closely resembles that of the sun, and the exis- 

 tence of from 15 to 20 per cent of polari/ed light, as shown by the careful observations of WRIGHT!'), 

 are in accordance with the meteoric theory ("). The above-mentioned observations were all visual. 



The first successful attempt to photograph the spectrum of the zodiacal light is described by PATH, 

 Lick Observatory Bulletin No. 165, from which the above-cited resume is taken. The results are 

 summed up as follows. 



"Upon developing the plate a spectrum was obtained which resembles the solar spectrum exactly, in 

 so far as can be judged from so small an object. 



"Two absorption-lines could be seen with certainty. A comparison of the plate with one of the sky 

 spectrum taken with the same slit-width showed these lines to be C and the blend of // and A of the 

 solar spectrum. 



I 1 ) Comptes Rcmlus 74, 262, 1872. 



l-l Astl'nn. Nach. 79, 327, 1872. 



I 3 ) Mont. Not. 32, 277, 1872. 



( J i Amor. Journ. of Sci. Srr. 3 8. 39, 187). 



I "'! Observatory 13, 77, 1890; Mon. YWatlirr Kcv. 34, 126, 1906. 



i r 'i Amcr. Jonrn. of Sci., Scr. 3, 7, 451, 187;. 



('I O. SEAKI.E, Mem. Amcr. Acnd. 11, 135, 1888. 



SKK'.ICFK, Munch. Bcr., 31, 265, 1901. 



(iEF.i.MUYiiK.N, Bulletin Astron., 19, .) )6, 1902. 



