32 Mr. J. N. Lockyer. Comparison of the Spectra of [Dec. 19, 



intermediate cool carbon stage is therefore not likely to be entirely 

 absent. 



The absence of the hot carbon fluting at 564 from the spectra of 

 nebulas may possibly be due to two causes. It is much fainter than 

 either 517 or 468-474, and may have escaped notice on that account ; 

 or, as in the nebula in Andromeda, it may be masked in the same way 

 as in comets. 



It is suggested that the ordinary nebulae are not hot enough to give 

 tbe line or fluting at 568, but it appears when the swarms become 

 more condensed, that is, in bright-line stars. The absence of 568 is 

 therefore probably due to the low temperature of nebulae. 



II. Comparison of Comets and Aurora. 



If we exclude the exceptional cases of Comet Wells and the Great 

 Comet of 1882, the number of lines and flutings recorded in comets 

 is small, and therefore only the most general list of auroral lines 

 must be taken for comparison. It would be unfair, for example, to 

 take the long list of lines given by Gyllenskiold. The lines stated 

 are taken from the table which I gave in a note in January, 

 1888,* which has since been slightly rearranged before taking the 

 means. 



1 Comets. 



Aurorae. 



Probable origins. 



\ of probable 

 origins. 





411 



H 



4101 



[426] 



426 



? 



? 



431 



431 



CH 



431 





435 



H 



434 



468—474 



474—478 



C (bot) 



468—474 



483 



482 



C (cool) 



483 



486 



486 



H 



486 



500 



500 



Mg 



5006 



517 



517 



C (hot) 



517 



519 



519 



C (cool) 



519 



521 



522 



Mg 



521 





531 



? 







535 



Tl 



535 





539 



Mn 



540 



546 



545 



Pb 



546 



558 



558 



Mn 



558 



561 





C (cool) 



561 



564 





C (hot) 



564 



568 





Pb, Na 



568 





606 



? 





[615] 



620 



Fe 



615 





630 



? 





• *. ? Roy. Soc. Proc.,' vol. 43, p. 321. 



