1888.] of the various Species of Heavenly Bodies. 



31 



while we know that in Comet Wells most of the luminosity at a certain 

 stage of the comet's history was produced by sodium. It is therefore 

 extremely probable that the view above put forward must be taken as an 

 explanation of the absence of D when not seen, rather than an abnor- 

 mal chemical constitution of the meteorites — that is to say, one in 

 which sodium is absent. This may even explain the fact that up to 

 the present time the D line of sodium has not been recorded in the 

 spectrum of any nebula. 



[Note. — In the lecture the author here referred to the spectrum of 

 o Ceti, as photographed by Professor Pickering for the Henry Draper 

 Memorial, the slide having been kindly placed at his disposal by the 

 Council of the Hoy al Astronomical Society. All the bright hydrogen 

 lines in the violet and ultra-violet are shown in the photograph, with 

 the exception of the one which is nearly coincident with H. The 

 apparent absence of this line is in all probability due to the masking 

 effect of the absorption line of calcium. In this case, then, it appears 

 that the calcium vapour was outside the hot hydrogen, and this there- 

 fore was being given off by the meteorites at the time. — April 18.] 



Detailed Discussions of the Spectra of some Bright-line Stars. 



These things then being premised, I now submit some maps to the 

 Society illustrating this part of the inquiry, although it will be some 

 time before my investigations on the bright-line stars are finished. 

 These maps will indicate the way in which the problem is being- 

 attacked, and the results already obtained. To help us in the work 

 we have first of all those lines of substances known to exist in 

 meteorites which are visible at the lowest temperatures which v:e can 

 command in the laboratory. We have also the results of the carbon 

 work to which reference was made in the previous paper ; and then 

 we have the lines which have been seen, although their wave-lengths 

 have in no case been absolutely determined in consequence of the 

 extreme difficulty of the observation, both in stars and in comets, 

 which I hold to be almost identical in structure. 



In the case of each star the lines which have been recorded in its 

 spectrum are plotted in the way indicated in the maps. The general 

 result is that when we take into account the low temperature radia- 

 tion, which we learn from the laboratory work, not only can we 

 account for the existence of the lines which have been observed, but 

 apparent absorptions in most cases are shown to be coincident witli 

 the part of the spectrum in front of a bright fluting. 



A continuation of this line of thought shows us also that, when in 

 these stars the spectrum is seen far into the blue, the luminosity 

 really proceeds first from the carbon fluting, and in the hotter stars, 

 from the hydrocarbon one, which is still more refrangible, in addition. 

 In the stars which have been examined so far, the dark parts of the 



