1888.] 



of the various Species of Heavenly Bodies. 



11 



an atmosphere like that of the sun seemed to supply the explanation 

 of the phenomena. 



Acting on this view in 1878,* I attempted to catch these chromo- 

 spheric lines in a Lyrae, abandoning the use of a cylindrical lens in 

 front of the slit with this object in view. 



Further, it was quite clear that if such gigantic supraphotospheric 

 atmospheres existed, their bright lines might much modify their real 

 absorption spectra ; even " worlds without hydrogen " might be thus 

 explained without supposing a lusus naturce, and so I explained 

 them. 



That this view is untenable, as I now believe, and that it is unneces- 

 sary, will, I think, be seen from what follows. A long series of newly 

 described phenomena, which are absolutely incomprehensible while it 

 is applied to them, find, I think, a simple and sufficient explanation. 

 I must hold that the view is untenable, because how a body constituted 

 in any way like the sun could change its magnitude from the thirteenth 

 to the sixth every year or so, or change its hydrogen lines from bright 

 to dark once a week, passes comprehension ; and the more closely a 

 "star " resembles the sun the less likely are such changes to happen. 

 Even the minor evolutionary changes are inexplicable on this hypo- 

 thesis, chiefly because in a completely condensed mass the temperature 

 must be very high and constant, while I have shown that the spectro- 

 scopic phenomena are those of a specially low temperature ; and I 

 may now add that many of the objects are extremely variable in the 

 quantity and quality of the light they emit. 



Another cause of the appearance of the hydrogen lines has been 

 suggested by Mr. Johnstone Stoney (' Roy. Soc. Proc.,' vol. 17, p. 54). 

 He considers it due to the clashing together of the atmospheres of two 



* " . . . The sun which we see, the sun which sends us the majority of the light 

 we receive, is but a small kernel in a gigantic nut, so that the diameter of the real 

 sun may be, say, 2,000,000 miles. Suppose then that some stars haye very large 

 coronal atmospheres ; if the area of the coronal atmosphere is small compared with 

 the area of the section of the true disk of the sun, of course we shall get an ordinary 

 spectrum of the star; that is to say, we shall get the indications of absorption 

 which make us class the stars apart ; we shall get a continuous spectrum barred by 

 dark lines. But suppose that the area of the coronal atmosphere is something very 

 considerable indeed, let us assume that it has an area, say fifty times greater than 

 the section of the kernel of the star itself ; now, although each unit of surface of 

 that coronal atmosphere may be much less luminous than an equal unit of surface 

 of the true star at the centre, yet, if the area be very large, the spectroscopic writing 

 of that large area will become visible side by side with the dark lines due to the 

 brilliant region in the centre where we can study absorption ; other lines (bright 

 ones) proceeding from the exterior portion of that star will be visible in the 

 spectrum of the apparent point we call a star. Now it is difficult to say whether 

 such a body as that is a star or a nebula. We may look upon it as a nebula in a 

 certain stage of condensation ; we may look upon it as a star at a certain stage of 

 growth."—' Koy. Soc. Proc.,' vol. 27, 1876, p. 50. 



