1887.] 



Researches on the Spectra of Meteorites. 



145 



which, in each case the temperature is increasing, while on the other 

 arm of the curve we have that other condition in which we get first 

 vaporous combination, and then ultimately the formation of a crust 

 due to the gradual cooling of the mass. At the top of such a curve 

 we shall of course have that condition in which the highest tempera- 

 ture must be assumed to exist. In a letter to M. Dumas in the year 

 1872, I suggested that possibly the simplification of the spectrum of 

 a star might be associated with the highest temperature of the vapour, 

 and that idea seems to have been accepted by other observers since 

 that time. We shall have then stars of the first class at the top of 

 the temperature curve. On the one arm of the curve representing 

 increasing temperature we shall have at various heights those aggre- 

 gations which give us indications of a gradually increasing tempera- 

 ture brought about by collisions, beginning with meteorites as widely 

 separated as they can be to keep up any luminosity at all, and finally 

 vaporous condensations due to gravity. 



On the arm of the curve descending from stars of the first class to 

 dark bodies like, say, the companion to Sirius, we must place those 

 bodies where absorption of compound molecules is indicated. This 

 we find in stars of Class III6 of Vogel. But here a very interesting 

 question arises. Between stars of the first class and that of we 

 are bound to insert stars of Class II, already located naturally on the 

 ascending arm. * 



The Case of equal Temperatures on either Side of the Curve. 



Speaking roughly, it may be said that the construction of such a 

 curve as this suggests that similar or nearly similar temperatures 

 will be found on either side. This in the main, of course, is true ; 

 but it must be pointed out that, on the rising curve, the temperature 

 will be that, as a rule, of individual meteorites and the vapours given 

 out by them, while on the descending arm it will be the temperature 

 of the consolidated mass, whether vaporous or becoming solid. But 

 it is obvious that if we take two points near the top of the curve we 

 shall have very nearly the same temperature of the atmosphere, by 

 which I mean the temperature of the layers in either case which are 

 most effective in producing the phenomena of absorption. To take a 

 concrete case, stars of the second class are obviously, by the consent 

 of all, of a lower temperature than stars of the first class : on which 

 side, therefore, of the curve must they be placed ? Or, to take a 

 more concrete case still, our sun is a star of the second class : on 

 which arm of the curve must we place the sun ? Here we find our- 

 selves in a position of some difficulty, but it would appear that future 

 work may enable us really to divide stars of the second class into two 

 series, and if we can do so there is very little doubt that one series 

 will represent the phenomenon of decreasing temperature of the ab- 



