216 Prof. A. W. Bickevton on Cosmic Evolution. 



that the point for which w 2 4-t< 2 = may be at the apex of the 

 wave, and not outside the fluid, as it will generally be. 

 This condition is found to lead to 



c s/gfi cos 2my + 2yh-c? = 0, . . . (10) 



which can be satisfied, since c i >gh. With this we have of 

 course to combine 



y= h +%< ("» 



and the relation between the parameters is found to be very 

 approximately 



,'=¥> (12) 



5h 



giving -£- for the elevation in the highest wave. These values, 



however, hardly lie within the limits of this paper, since in 

 this extreme case/'ic will have the value '46 at the crest of 

 the wave. 



XVII. Cosmic Evolution. By Prof. A. W. Bickerton *. 



IN this paper the term galactic system will mean not only 

 the milky way, but also the caps of nebulse at its poles. 

 The term milky way will be used to imply the galaxy itself. 

 The term cosmic system will be applied to aggregations of 

 dimensions comparable to the Magellanic clouds and to our 

 own galactic system. (In my earlier papers these masses 

 were called universes ; but Lord Kelvin and Lord Rayleigh 

 independently pointed out that this name might mislead, I 

 have consequently substituted cosmic systems.) The term 

 cosmic system of the first order applies to aggregations 

 without definite structure, in which no general collision has 

 occurred. In systems of the second order, a single general 

 collision has taken place, and the symmetry is perfect. All 

 other cosmic systems are of the third order. In these more 

 than one general collision has occurred, and there is too much 

 symmetry to be of the first order, and too little symmetry to 

 be of the second. The visible universe (the galactic system 

 of which our solar system is a part) is consequently a system 

 of the third order. 



The group of recently-discovered monatomic elements that 

 have no combining power, namely, helium, neon, argon, cry pton, 

 and xenon, I call cosmic pioneers. They are practically 

 * Communicated by Prof. A. W, Riicker, Sec.R.S. 



