48 Mr. J. N. Lockyer. On the Classification [Apr. 12, 



These differences may at first sight be taken as indicating a higher 

 temperatnre in the first of these stars than in either of the others, bnt 

 further investigation seems to indicate this is not the case. The con- 

 tinuous spectrum from the meteorites is very faint in each case, and 

 on it is superposed bright carbon, that in the blue showing itself as a 

 separate bright band, 468. The curve rises in each star at 564 carbon, 

 and is high in the position 517. 



It will be seen from the light curves that the rise at 564 is less in 

 1st Cygnus than in either of the other stars, and the end of the 

 fluting 558, due to the manganese, becomes visible as a line in this 

 star, while in 2nd and 3rd Cygnus the carbon at 564 with this fluting 

 produces such a brightening of the spectrum that the manganese 

 cannot be seen as a bright line. In 2nd Cygnus the 564 carbon 

 is nearly equal in brightness to the 558 manganese flutiDg, and these 

 produce together such an intensely bright patch between those wave- 

 lengths that we get apparent dark spaces on each side of it. The 

 540 line of manganese has a considerable difficulty in showing itself 

 on the bright spectrum due to meteorites and carbon combined, 

 whereas in 1st Cygnus where the radiation of carbon is weaker the 

 line is very bright. The invisibility of 507 and 527 in the spectra of 

 2nd and 3rd Cygnus stars is therefore due probably to the extra 

 brightness of the fluting spectrum due to carbon, rather than to the 

 lower temperature of these stars. The greater number of lines in 

 1st Cygnus indicates therefore a lower temperature than in the other 

 stars, and this conclusion is borne out by the appearance of the 636 

 line in 2nd and 3rd Cygnus, and its absence from 1st Cygnus. 



The conclusion which has been arrived at after a careful considera- 

 tion of these stars is that 1st Cygnus is the coolest, 2nd Cygnus ranks 

 next above in temperature, and 3rd Cygnus is the hottest of the three. 



With regard to the line in 2nd and 3rd Cygnus at 636 there is an 

 element of doubt as to the true position. Vogel does not give the 

 wave-length in his list of lines, neither does he show it in his sketch 

 of the spectrum, but he* indicates its position on the light curve, and 

 from this a curve had to be drawn and the wave-length ascertained as 

 nearly as possible. Yogel suggests the line may be the hydrogen C 

 line, but this seems very improbable, since F is absent, and although 

 F is frequently recorded in bright-line stars without C, in no case is 

 C given without F. It may be the C line is seen clearly because 

 there is no continuous spectrum near it, while F is not visible on 

 account of the bright spectrum around it. 



The above stars are not the only ones with bright lines in the 

 constellation Cygnus. 



A recent communication by Professor Pickering gives the following* 

 additional information : — * 



* * Nature,' September 9, 1886. 



