1892.] 



On Nova Auriga?. 



491 



ruarv, we were sure that small alterations were taking place in this 

 line, and that the component on the blue side no longer maintained 

 its superiority. We suspected, indeed, at times that the line was 

 triple, and towards the end of February and in the beginning of 

 March we had no longer any doubt that it was occasionally divided 

 into three bright lines by the incoming of two very narrow dark lines. 



Similar alterations, giving a more or less apparent multiple char- 

 acter to the lines, are to be seen not only in the bright lines, but also 

 in those of absorption in contemporary photographs taken of the spec- 

 trum of the star. I may mention those taken at Potsdam, Stony- 

 hurst, and the Lick Observatory. They were specially watched and 

 measured by M. Belopolsky at Pulkova. 



Professor Pickering informs me that on a photograph taken at 

 Cambridge, U.S., on February 27, H, K, and « are triple, and that 

 Miss Maury recorded, "the dark hydrogen lines rendered double, and 

 sometimes triple, by the appearance of fine bright threads superposed 

 upon the dark bands." 



To explain these appearances on the assumption that each com- 

 ponent of the bright and dark lines is produced by the emission or 

 absorption of hydrogen moving with a different velocity would 

 require a complex system of six bodies all moving differently. 



A much more reasonable explanation presents itself in the phe- 

 nomena of reversal, which are very common on the erupted solar sur- 

 face and in the laboratory.* 



Professor Liveing informs me that he and Professor Dewar, in their 

 researches with the arc-crucible, met with cases in which, through the 

 unequal expansion of the bright line on the two sides, the narrow re- 

 versed dark line did not fall upon the middle of the broader bright 

 line, but divided it unsymmetrically. This effect was notably shown 

 in photographs which they took of the spectrum of zinc. Unsym- 

 metrical division of the lines by reversal would also come in, if the 

 cooler and hotter portions of the gas were possessed of relative 

 motion in the line of sight. 



* [M. Deslandres permits me to quote the results of his recent observations on 

 this point : — " Lorsque Ton dirige sur la fente d'un spectroscope de grande disper- 

 sion 1' image d'une facule du soleil on a invariablement avec les raies H et X du 

 calcium un renversement triple. Meme lorsque les facules sont larges et intenses, 

 on obtient encore le renversement triple avec des raies brillantes centrales, plus 

 faibles il est vrai, si Ton envoie dans le spectroscope la lumiere de tous les points 

 du soleil, comme c'est le cas pour les etoiles ; par exemple en dirige ant le collima- 

 teur vers le soleil sans l'intermediaire d'aucun objectif, ou encore en le dirigeant 

 vers un point quelconque du ciel. Si les facules sont au centre la raie centrale est 

 a sa place normale, si elles sont a Test ou a l'ouest la raie centrale est deplacee 

 legerement (2 kil. au plus) mais deplacee surement. Au point de vue pratique 

 cette proprigte fournit un moyen de reconnaitre l'etat general de la surface solaire 

 lorsque le soleil est cache par les nuages." — June 20.] 



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