Prof. A. W. Bickerton on Cosmic Evolution. 221 



The kinematic condition of the impact would exactly pro- 

 duce such a system. It is now known to be a rough double 

 spiral of stars, with sprays and streams of stars and two caps of 

 nebulae. It is not difficult to picture the kinematic conditions 

 necessary to form such a rough ring, or double spiral of stars 

 with polar caps of nebulous matter. 



Let us assume a complete whirling coalescence of two cosmic 

 systems in which the part coming into collision is considerable. 

 This heated part is in the centre of the system. Here all the 

 material is volatilized, and the pressure produced can find no 

 relief save axially; hence the system is, as it were, a short 

 cannon open at each end, and the discharged gas spreads 

 itself over the poles of the system. 



This discharge, that is commenced by pressure, is finished 

 by molecular escape. Globular nebulas form in this gaseous 

 matter by the attraction produced by wandering bodies 

 plunging into the gas. The globular nebulas so produced 

 attract one another and become double nebulae; they are then 

 wrought into spindles, spirals, dumbbells, or rings by the 

 kinematic peculiarities of the varying depths of impact. 



It is significant that temporary stars, planetary nebula?, and 

 all the bodies likely to be produced by the impact of stars are 

 in the milky way; and all the forms of nebulae deduced as 

 resulting from the impact of nebulae are where we should 

 expect them to be, namely, at the poles of the milky way. 



If this generalization represents the mode of nature's action, 

 then there is a possibility that the entire cosmos is immortal, 

 and the present order but a phase of an eternal rhythm. 



The sequence of these agencies is as follows? — 



(1) Diffusion of heat by radiation. 



(2) This radiation, falling on the dust of space, heats it. 



(3) The heat of this cosmic dust is taken away by slowly 



moving light molecules having their velocity 

 increased. 



(4) Free molecules are also sent out of systems by partial 



impacts, by selective molecular escape, and other 

 agencies. 



(5) Free molecules will remain longest in the position of 



maximum potential where their motion is least, and 

 will consequently tend to aggregate in the empty 

 parts of space. 



(6) By the interaction of three bodies the velocity 



acquired by one sometimes takes it out of the cosmic 

 system. 



