1893.] Bands in the present Spectrum of Nova Aurigce. 33 



brighter which form the termination of the group towards the blue ; 

 a line nearly as bright about the middle of the group ; and a third 

 prominent line at the end of the group towards the red. 



We have little doubt, though we hesitate to state it positively, that 

 the space between the two brightest lines, that on the blue side of 

 the bright line in the middle of the group, and the spaces on the blue 

 sides of some others of the lines, were darker than the faint luminous 

 background, in which case we should have to do possibly with lines 

 of absorption of the same substances shifted towards the blue. A 

 few only of the finer bright lines which were occasionally glimpsed 

 between the more brilliant lines have been put into the diagram. 



The pair of bright lines at the termination of the group towards 

 the blue makes this the brighter end of the group, which does not, 

 however, as a whole possess any of the usual features of a fluting. 



On February 10, the micrometer webs were placed so as just to 

 include the bright lines of the group, but not the faint background 

 which at the clearest moments could be traced for some distance, 

 especially at the blue end of the group. The instrument remained 

 untouched, and the position given in the diagram is that found from 

 the places of the micrometer webs upon the solar spectrum, on Row- 

 land's scale, as observed on the following morning. 



On the 26th measures of this group were made relatively to the 

 position of the principal line in the nebula of Orion ; these gave also 

 almost exactly the same position in the spectrum for the group, but, 

 as we have already stated, all these measures are unfortunately 

 liable to a small error from the possible flexure, at that time, of a 

 part of the instrument. 



The mean of Mr. Campbell's measures at the Lick Observatory, 

 during the period of our observations, from February 10 to Feb- 

 ruary 27, gives X 5006 for the middle of the band. He remarks : 

 "In any discussion of these observations it is necessary to take into 

 account the difficulty of accurately locating the centre of a line so 

 broad and diffuse as this one is."* 



In another place Mr. Campbell says : " The line is at least 8 tenth- 

 metres broad and the edges very diffuse."! 



These observations would be brought into accordance with our own, 

 so far as relates to the length and the position of the band, if we sup- 

 pose Mr. Campbell to have observed only the more refrangible and 

 much brighter half of the whole group. J 



* ' Astronomy and Astro-Physics,' May, 1893, pp. 418, 419. 



f Publ. Ast. Soc. Pacific,' vol. 4, p. 246. 



% Professor Campbell also says : " On August 30 the line was suspected to be 

 double, and the grating measures of that night refer to a point midway between the 

 two condensations. On September 7 the measures refer to a point of maximum 

 brightness slightly less refrangible than the centre of the line." ' Astronomy and 

 Astro-Physics,' Oct., 1892, p. 718. 



VOL. L1V. D 



