1892.] 



On Nova Aurigce. 



487 



the spectrum of terrestrial hydrogen, C was narrower than F, which 

 again was less broad than H y near G. 



The remarkable phenomenon presented itself that all the bright 

 hydrogen, lines and some other of the bright lines were doubled by 

 a dark line of absorption of the same gas on the blue side. The 

 shift of the dark hydrogen lines towards the blue showed a velocity 

 of approach of this cooler gas somewhat greater than the recession 

 of the gas emitting the bright lines. Our estimates of the relative 

 velocity would place it at about 550 miles a second, which is in good 

 accordance with the result obtained by Professor Vogel from the 

 measurement of his photographs. 



So far as our instruments enabled us to determine the point under 

 the unfavourable condition of the rapidly waning light of the star, 

 no great change in the relative motion of the gases producing the 

 bright and dark lines took place from February 2 to about March 7, 

 when the star's light became too faint for such observations — a 

 result which we believe to be in accordance with successive photo- 

 graphs taken at Potsdam, Cambridge (U.S.), Stony hurst, and some 

 other observatories. 



Comparison with Sodium. — A bright line, which on one occasion we 

 glimpsed as double, appeared about the position of D. 



Direct comparisons with a sodium flame, while leaving no doubt 

 that the line was due to this substance, showed that it was shifted, 

 similarly to the bright hydrogen lines, towards the red. Perhaps we 

 should state that at the time we had the impression that this line 

 was not shifted to so large an amount relatively to sodium as was the 

 F line relatively to hydrogen. As the comparison was more difficult 

 at this part of the spectrum, and one prism only was used, we do not 

 attach importance to this observation. 



Comparisons with Nitrogen and Lead. — There can be little doubt 

 that one of the four brilliant lines in the green is the same line 

 which appeared in the Nova of 1876, and was at that time suspected 

 to be the chief nebular line. Very great pains were taken to ascer- 

 tain its exact position and character. 



For this purpose, on February 2, and again on February 3, direct 

 comparisons were made with the more powerful spectroscope of the 

 star's line with the brightest double line of the nitrogen spectrum, 

 and also with a line of lead, to which line the near relative posi- 

 tion of the nebular line is accurately known. Comparisons on 

 both nights, and with both lines, showed that the star line was 

 certainly less refrangible than the chief nebular line, and by a much 

 larger amount than the shift of F relatively to hydrogen. A similar 

 conclusion has been arrived at by Professor Young, Professor Yogel, 

 Dr. Campbell at the Lick Observatory, Father Sidgreaves, Dr. Becker, 

 and M. Belopolsky at Pulkova. The position of the line in the star 



