1892.] on the New Star in Auriga. 621 



refrangible end, the positions of which M. Deslandres informs me 

 fall into Balmer's formula for the hydrogen series.* 



The resemblance of the spectrum of the Nova to that of the 

 erupted solar surface is further shown in a remarkable feature of 

 great significance in the character of the hydrogen lines both bright 

 and dark. On February 2nd we noticed that the F line was not of 

 uniform brightness throughout its breadth. We soon came to the con- 

 clusion that it was divided, not quite symmetrically, by a very narrow 

 dark line. The more refrangible component was brighter, and 

 rather broader than the other. Later on in February, 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 component on the blue side no longer maintained its superiority.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 v^as occasionally divided into three bright 

 lines by the incoming of two very narrow dark lines. 



Similar alterations, giving a more or less apparent multiple 

 character 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 spectrum of the star. I may mention those taken at Potsdam, 

 Stony hurst, and the Lick Observatory. These changes were specially 

 watched and measured by M. Belopolsky at Pulkova. 



Prof. Pickering informs me that on a photograph taken at Cam- 

 bridge, U.S., on February 27th, H, K, and a are triple, and that Miss 

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

 sometimes triple, by the appearance of fine bright threads super- 

 posed upon the dark bands." 



Now, when on the sun's surface, or in the laboratory, portions of 

 the same gas at different temperatures come in before each other, the 

 cooler gas may cause a narrow absorption line to form upon a broader 

 bright line, and thus impart to it the appearance of a double line; 

 or in the case of hotter gas, a narrow bright line upon a dark line. 

 Prof. Liveing and your distinguished Professor of Chemistry, Prof. 

 Dewar — whose researches with the electric arc-crucible have made 

 them specially familiar with the ever-changing guises and disguises 

 of this protean phenomenon of reversal — have recorded cases not only 

 of double reversals, giving apparent . triplicity to single bands, but 

 also of threefold reversals. The phenomenon of the unsymmetrical 

 division of the bright and dark lines which was occasionally seen in 

 the Nova frequently presents itself in the laboratory from the unequal 

 expansion on the two sides of the line on which the reversed line 

 falls ; and at the solar surface from the relative motions in the line 

 of sight of the hotter and cooler portions of the gas taking part in 

 the phenomenon. Unless we accept this obvious interpretation of 

 the apparent multiple character of the stellar lines, we should have 



* M. Deslandres has detected siDce two more lines, thus adding five new 

 lines to the hydrogen series. 



