50 



Mr. G. J. Stoney on the Physical 



[Recess, 



fate of hydrogen in a Orionis, ft Pegasi, and the other stars in which there 

 are no lines corresponding to the solar lines C and F. If, however, the 

 lines that are in this way withdrawn be as few as the lines of hydrogen, 

 their absence will not sensibly affect the colour of the star. And finally, 

 such conditions may prevail upon particular stars as will enable a spectrum 

 of the first order to present itself, — that kind of spectrum in which the 

 usual scattered lines of a spectrum of the second order are replaced by a 

 multitude of fine closely ruled lines arranged in groups of regularly shaded 

 bands, so as to give to the spectrum of the gas the appearance of a fluted 

 pillar. The bands in the spectra of a Ononis, /3 Pegasi, and some others 

 probably arise in this way, and perhaps from some compound of hydrogen*. 

 The lines constituting such bands will be affected by differences of the force 

 of gravity in the same way as other lines, and will therefore, if distributed 

 with tolerable impartiality over the spectrum, cooperate with them in produ- 

 cing that tendency towards a ruddy hue which belongs to stars that exercise 

 a feeble attraction at their surfaces. It may be noted that in none of the 

 figures which Mr. Huggins has given of the spectra of solitary stars with 

 shaded bands, do they seem crowded abnormally over the yellow, orange, 

 and red, but rather the reverse. 



86. We are now in a position to appreciate the significance of the pheno- 

 mena which the spectral examination of stars has brought to light. We can 

 easily see why in the class of bluish-white stars of which Sirius and a Lyras 

 are types, stars at whose surfaces the force of gravity is greater than on our 

 sun, " the dark lines they present in great number are all, with one excep- 

 tion, very thin and faint, and too feeble to modify the original whiteness of 

 the light," and why "the one exception consists of four very strong single 

 lines, one line corresponding to Fraunhofer's C, one to F, and another 

 near G"f . There can be little doubt that the multitude of faint lines will 

 prove to be due almost exclusively to iron aud the substances near it in 

 vapour-density, such as calcium, chromium, manganese, nickel, and cobalt, 

 with of course sodium and magnesium. These, with the exception of so- 

 dium and magnesium, can produce only lines which are faint through the 

 whole extent of the spectrum, since when attracted down with so much 

 force as they are by the stars they cannot exist beyond regions of elevated 

 temperature. And substances a little higher in vapour- density will be un- 

 able to endure even the chill of the photosphere, and therefore shrink 

 within it. The violet and indigo rays being in these stars not subdued by 

 lines in the same way as they are in the sun, gives to the whiteness of the 

 stars a somewhat coloured tinge in eyes, like ours, accustomed to adjudge 

 the sun's light to be white. 



* If this surmise is well founded, the compound must be sought among the compounds 

 of hydrogen of low vapour-density, such as marsh-gas (mass of molecules 8), ammonia 8-5, 

 water 9, defiant gas 14, methylamine 15-5, sulphuretted hydrogen 17, phosphuretted 

 hydrogen 17, hydrochloric acid 18-25,. &c. 



t Huggins's Lecture before the British Association at Nottingham, published by Ladd. 



