

1890.] Rayet's Bright-Line Stars in Cygnus. 35 



an absolute coincidence of the band in all three stars with the bine 

 band of a spirit-lamp flame.* 



As the presence or absence of carbon in these stars, as shown by 

 the coincidence or otherwise of the bine band with that of the hydro- 

 carbon flame, was of great importance to us in connexion with a 

 wider investigation on which we are at work, we thought it necessary, 

 after these recent statements as to the position of the band, to make 

 direct comparisons of the spectra of these stars with that of the hydro- 

 carbon flame under sufficiently large dispersion to enable us to deter- 

 mine whether Vogel's measures are substantially correct, or whether 

 they are so largely in error as the absolute coincidence of the band 

 with the blue band of a spirit-lamp flame in the case of all three 

 stars would show them to be. 



The obvious importance of making the observations with sufficient 

 dispersion is supported by Yogel's own experience. With the small 

 dispersion which he employed in his earlier observations in 1873, he 

 did not detect the large difference of position, about X 0040, of the 

 band in No. 4001, as compared with its position in the other two 

 stars. On this point Vogel says, in his memoir of 1883 : " Etwas 

 abweichend ist nur die Auffassung der Lage der breiten hellen Bande 

 im Blau, die bei den friiheren Messungen bei alien drei Sternen 

 ubereinstimmt. . . . Bei den verhaltnissmassig geringen optischen 

 Hiilfsmitteln, mit denen jene Messungen ausgefiihrt wurden, ist die 

 Uebereinstimmung aber eine ganz iiberraschende " (Zoc. cit., p. 21). 



We observed the spectra of the stars successively, first with a direct 

 vision prism of small dispersion, then with a spectroscope (A) con- 

 taining one prism of 60, and finally with a spectroscope (B) with 

 two compound prisms, equal to about four prisms of 60 ; with the 

 last-named instrument the comparisons with the hydrocarbon flame 

 were made. 



A rapid preliminary comparison in the spectroscope (B) of the 

 spectra of the three stars with the blue base of a Bunsen flame 



* Professor Lockyer, in a signed article in ' Nature ' (August 7, 1890, vol. 42,. 

 p. 344), writes ; 



" In the Bakerian Lecture for 1888 I gave a complete discussion of the spectra of 

 bright-lined stars, as far as the observations went, and the conclusion arrived at was 

 that they were nothing more than swarms of meteorites a little more condensed than 

 those which we know as nebulae. The main argument in favour of this conclusion 

 was the presence of the bright fluting of carbon which extends from 468 to 474. 

 This standing out bright beyond their short continuous spectrum gives rise to an 

 apparent absorption band in the blue. . . . Direct comparisons of the spectrum 

 of all the three stars in Cygnus with the flame of a spirit-lamp have been made by 

 Mr. Fowler, and these showed an absolute coincidence of the bright baud in the 

 stars with tbe blue band of carbon seen in the flame. It was found quite easy to 

 get the narrow spectrum of the star superposed upon the broader spectrum of the 

 flame so that both could be observed simultaneously." 



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