1868.] 



Constitution of the Sun and Stars. 



51 



87. On the other hand, Aldebaran is a good sample of a star which exerts 

 less attraction at his surface than the sun, but which in other respects 

 differs little from him. All the gases which cause solar lines can rise in 

 the atmosphere of Aldebaran to colder heights than they can on the sun, 

 and, as a consequence, they encroach more upon the violet end of his spec- 

 trum, and thus give to his light its rose-like tint. Another consequence is, 

 that substances present themselves in the star's outer atmosphere with 

 vapour-densities so high that the sun's superior attraction keeps them im- 

 prisoned within his photosphere. Mercury, mass of molecules 100; anti- 

 mony, 122©; tellurium, 129; bismuth*, 210(?). 



88. All the foregoing appearances present themselves in aOrionis, which 

 is therefore also a star on which the force of gravity is less than on the 

 sun. They are found in a Orionis with the addition of a spectrum of the 

 first order, one of whose bands has been observed to fluctuate in distinct- 

 ness. We have reason to suspect, therefore, that the changes of bright- 

 ness of this star, which is slightly variable, arise from some cause which 

 alters periodically the temperature of the upper layer of that gas in its at- 

 mosphere from which the spectrum of the first order comes. 



Section II. — Of Multiple Systems-\. 



89. Hitherto we have considered only the case of stars uninfluenced by 

 one another. If, however, two stars should be brought by their proper 

 motions very close, one of three things would happen. Either they 

 would pass quite clear of one another, in which case they would recede to 

 the same immensity of distance asunder from which they had come ; or 

 they would become so entangled with one another as to emerge from 

 the frightful conflagration which would ensue as one star ; or, thirdly, 

 they would brush against one another, but not to the extent of preventing 

 the stars from getting clear again. It is this last cause which we must now 

 closely examine. After the stars disengage themselves they will be found 

 moving in new orbits, which, if their motions before contact had been pa- 

 rabolic, will become elliptic. They will therefore return again and again, 

 and at each perihelion passage will become engaged. If we take into account 

 only the tangential resistance which the atmosphere of each presents to 

 the motion of the other, we shall find^ that the mean distance -of the 



* See Table I. p. 16. 



f The following attempt to trace double stars, the solar system, and the amazing store 

 of heat which we find in nature, to a proximate mechanical origin, is brought forward in 

 the hope that it will prove of service in guiding inquiry, and in other ways ; as an hypo- 

 thesis always should, if not abused, which strikingly accords with many of the pheno- 

 mena, and admits of being refuted or strengthened by future observations. I trust this 

 will be accepted as a sufficient apology for offering to the scientific public what is as yet, 

 of necessity, a speculation. 



+ These results appear from the following formulae of elliptic motion: — 



2 _? = t-C^l\ 

 6 r jA/3 2 J> 



E 2 



