434 Note on the Spectrum of Nova Aurigce. [Feb. 11, 



In addition to the lines recorded in the table, the photographs of 

 the spectrum of the Nova showed several lines more refrangible than 

 K. These have not yet been reduced, but they probably include 

 some of the ultra-violet hydrogen lines. 



All the lines in the spectrum of the Nova are broad, although in a 

 photograph of the spectrum of Arcturus, taken with the same instru- 

 mental conditions, the lines are perfectly sharp. It is important 

 to note that the broadening of the lines is not accompanied by any 

 falling off of intensity at the edges, as in the case of the hydrogen 

 lines in such a star as Sirius. With the method employed in taking 

 the photographs, long exposures are liable to result in a thickening 

 of all the lines, on account of atmospheric tremors. The lines would 

 also be thick if the Nova be hazy, as observed at Greenwich. In the 

 photographs, however, all the lines are not equally thick. 



If the lines are similarly broadened when a slit spectroscope is 

 employed, the effect must be due to internal agitations; for if different 

 regions of the Nova are moving with varying velocity, or with the 

 same velocity in different directions, a normally fine line might be 

 widened, as observed in the photographs. 



The hydrogen lines and the K line of calcium are very bright, and, 

 as pointed out in the note above, they are accompanied by dark lines 

 on their more refrangible sides. This was previously noticed in the 

 photographs taken on February 3, but as the dark lines were not very 

 conspicuous, they were not referred to until further confirmation 

 had been obtained. 



It appears from a note in the * Standard ' newspaper, February 10, 

 that dark lines have also been observed on the more refrangible 

 sides of the bright hydrogen lines in the photographs taken at 

 Harvard College Observatory. 



A somewhat similar phenomenon has already been recorded by 

 Professor Pickering, in the case of ft Lyra3, and this has been con- 

 firmed by a series of photographs taken at Kensington. In this 

 case, the bright lines are alternately more and less refrangible than 

 the dark ones, with a period probably corresponding to the known 

 period of variation in the light of the star. The maximum relative 

 velocity indicated is stated by Professor Pickering as approximately 

 300 English miles per second. 



In the case of Nova Aurigas, the dark lines in all four photographs 

 taken at Kensington are more refrangible than the bright ones, so 

 that as yet there is no evidence of revolution. The relative velocity 

 indicated by the displacement of the dark lines with respect to the 

 bright ones appears to be over, rather than under, 500 miles per 

 second. The reduction is not yet complete. 



Should the photographs which may be obtained in the future con- 

 tinue to show the dark lines d : splaced to the more refrangible side of 



