146 



Mr. J. N. Lockyer. 



[Nov. 17, 



sorbing layers, wliile the other series will represent the phenomenon 

 of increasing temperature. 



What considerations are likely to help us in such an inquiry as 

 this ? The atmosphere of a star built up by meteorites should 

 resemble in its constitution the totality of the chemical constitution 

 of meteorites, and therefore it might be inferred that the spectro- 

 scopic phenomena presented by such an atmosphere would not be 

 widely different from the spectroscopic phenomena presented by the 

 vapours of many meteorites volatilised together. 



To investigate this question I have obtained composite photo- 

 graphs of the spectra of several meteorites, with a solar spectrum for 

 purposes of comparison. I find that, while, on the one hand, the 

 composite photograph giving us the spectrum of the meteorites 

 greatly resembles that of the sun, as it should do, there are some 

 variations which suggest the line of separation to which I have 

 before alluded. From Dr. Huggins's magnificent photographs of the 

 stars we have learned that, as I had predicted years before the 

 photographs were taken, the thickness of H and K varies very 

 greatly in different stellar spectra. In those stars, presumably the 

 hottest ones, in which we get the series of hydrogen lines almost 

 alone as great absorbers, K is almost absent ; it finally comes in, 

 however, and after a certain stage has been reached it is the most 

 important line in the spectrum. But there are stars in which the 

 lines h and Gr of hydrogen are not very much more developed than 

 they are in the case of our own sun, in which K is much thinner than 

 in the solar spectrum ; and associated with this condition of K there 

 is the absorption of a hydrogen line more refrangible than K at wave- 

 length 3800, which is not represented in the solar spectrum with 

 anything like the intensity. The question arises, therefore, whether 

 the enormous thickening of K observed in the sun and some other 

 stars may not be limited to those stars which, like our sun, are 

 reducing their temperature ; for we certainly are justified in assum- 

 ing that the temperature of the sun now is not so high as it was in an 

 earlier stage of the development of the system. Such a difference as 

 that, if it is subsequently established, can only come from the atmo- 

 sphere, as an effect of cooling, becoming richer in those substances 

 the lines of which get broader as the star cools down. We can easily 

 imagine that during the process of cooling the relative quantities of 

 the vapours should not always remain constant, although it is im- 

 possible in the present state of our knowledge to give any particular 

 reason why such and such vapours should disappear from the 

 spectrum in consequence of chemical combinations, while others 

 should develop apparently in consequence of their retirement. 



