84 



NATURE 



{Nov. 24, 1887 



a Orionis. 



Vogel. — Biobachtungen zu Boihkamp, Heft. i. p. 20. 



R Geminorum. 



Vogel. — Astronomische Nachrichten, No. 2000. 



Meteorite G16w. 



Work at Kensington. 



Schjellerup 152. 



Vogel. — Publicationen des Astrophysikalischen Observa- 

 toriums zu Potsdam, vol. iv. No. 14, p. 30. 



On the Absorption Phenomena of Stars with Bright Lines. 



In addition to the map showing the bright lines visible in those 

 stars the spectra of which contain them, I have prepared 

 another map showing the absorptions which also occur. The 

 two maps present a remarkable agreement — that is to say, there 

 is the same progression in the absorption phenomena as there is 

 in the bright-line phenomena. In those stars in which bright 

 lines are seen without the lines of hydrogen (in which stars the 

 meteorite swarm is probably at a slightly higher temperature 



than that observed in the nebula when only the line at 500 is 

 visible) we have no marked absorption-lines, but rather bands. 

 When the hydrogen lines are added, as in 7Cassiopeise, then we 

 get the absorption of sodium and b of magnesium, as we should 

 expect. The individual meteorites therefore are much cooler in 

 these stars than in the Novas, seeing that the absorption is so 

 little developed. Speaking generally, therefore, we may say 

 that there are two causes of minimum absorption phenomena in 

 stars. In the first place, as in the bright-line stars, only little 

 vapour surrounds each meteorite, and that vapour consists of 

 the substances visible at the lowest temperature ; while, on the 

 other hand, in stars like Sirius, in consequence of the absolute 

 state of vapour, we only get practically the absorption of hydro- 

 gen, or at all events the absorption of hydrogen in great excess, 

 due, I have very little doubt, in part, to the fact that most other 

 substances have been dissociated by the intense heat resulting 

 from the condensation of the meteorites. 



Notes on the Provisional Temperature Curve. 



In order to bring the various results referred to in this 

 communication in a definite form before my own mind, I have 

 prepared a diagram which I have called a temperature curve, so 



CLASS \CL oL LYRAEl 

 PREDOMINANT H ABSORPTION. J 



CLASS \\a 



HIGH TEMPERATURE 

 ME.TE0R1TIC UNE ABSORPTION 



CLASS 1(1^. 



BRIGHT C&, I 



Mn&Zn FLUTING I 



AESORPTION.'' 



CLASS \c 

 y cA5siopEi;t 



aiTTlE ABSORPTION 

 BRIGHT H. 



CLASS 112 



i 



BRIGHT LINES 

 NEBULA. ) 



STARS with! 



BRIGHT LINESIWITHOUT • 



H. ;. 



NEBUL/t. ' ■■■■-■ 



CLASS \\a. 



?) CLASS 111^ 



CARBON ABSORPT[ON 



Provisional Temperature Curve. 



that on one side of it we may consider those stages in the 

 various heavenly bodies in 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 temperature 

 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 aggregations which give us indica- 

 tions of a gradually increasing temperature 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 indi- 

 cated. This we find in stars of Class III.^ of Vogel. But 



here a very interesting question arises. Between stars of the first 

 class and that of lll.b we are bound to insert stars of Class II., 

 already located naturally on the ascending arm. 



The Case of Equal Temperatures 07t 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 tempera- 

 tures 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 mo^t 

 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 



