470 Transactions. —Miscellaneous. 



stable, the velocity not overcoming the attraction. In a small 

 graze the body ^Yill expand indefinitely in consequence of its 

 small attractive power, and every particle will have so high a 

 velocity that it will, in general, become an independent wan- 

 derer in space. 



18. Space will consequently be dusty with free molecules. 



19. The mass of gas will obviously expand temporarily 

 into a hollow shell of gas. Herschel tells us this is the con- 

 dition of planetary nebulse. 



20. A partial impact of stars will consequently generally 

 produce in less than an hour an intensely heated body that 

 will expand enormously without much diminution of heat. It 

 will consequently become very bright indeed. It will then 

 continue to expand until it becomes a planetary nebula. 

 Then it will disappear by dissipating completely into space. 



21. The molecules on the far side of the sphere will be 

 retreating from us ; those on the near side advancing towards 

 us. The spectrum of such a body will consequently be crossed 

 by broad bright bands, each with a maximum in the centre, 

 and gra.dually dying imperceptibly away. If this body has 

 any motion in the line of sight, as it probably will have when 

 the two colliding stars are unequal, the line of maximum 

 intensity, although in the centre of the band, will be displaced 

 from its true position. 



22. Immediately after the impact the temperatures of 

 different kinds of molecules will be very different from each 

 other. "Were the colliding spheres of oxygen they would be 

 sixteen times as hot as if they were similar spheres of hydro- 

 gen. The temperature at impact will be proportionate to the 

 atomic weight. 



23. In a niixed sphere these inequalities of temperature 

 would quickly equalise themselves. Then when the tempera- 

 ture was uniform the hydrogen would be moving four times 

 as fast as the oxygen. The velocities vfould vary inversely 

 as the square root of the atomic weights. 



24. This difference of velocity will tend to sort the molecules 

 into layers like a lily-bulb, the hydrogen on the outside fol- 

 lowed by lithium, &c., in the order of their atomic weights. If 

 there are elements lighter than hydrogen, as spectroscopic 

 observations of the corona suggest, these will, of course, pre- 

 cede hydrogen. In my lectures and papers on this subject I 

 have called this action " selective escape." 



25. Space will be thickly spread with free molecules of the 

 lightest elements. This fact is important as one of the in- 

 teresting agencies that prevent the theory of dissipation of 

 energy being of cosmic application. 



26. A telescopic view of a new planetary nebula produced 

 by a partial impact, if looked at through a prism, should give 



