288 DISCUSSIONS IN COSMOLOGY. 



The formation of a sun by collision is an event that 

 would not be likely to escape observation if it occurred 

 within the limits of visibility in space. But such an 

 event must be of very rare occurrence, or the number 

 of stars visible would be far greater than it is. The 

 number of stars registered down to the seventh magni- 

 tude, inclusive, is — according to Herschel — somewhere 

 between 12,000 and 15,000, and this is all that can 

 possibly be seen by the naked eye. Now, if we suppose 

 each of them to shine like our sun for (say) 100 million 

 years, then one formed in every 7000 or 8000 years 

 would maintain the present number undiminished. 

 But this is the number included in both hemispheres, 

 so that the occurrence of an event of such unparalleled 

 splendour and magnificence as the formation of a star 

 or rather nebula — for this would be the form first 

 assumed — is what can only be expected to be seen on 

 our Hemisphere once in about 15,000 years. 



The absence of any historical record of such an event 

 having ever occurred can therefore be no evidence 

 whatever against the theory. 



Age of the Sun in relation to Evolution. — One of 



In the latter case he considers a double star is formed. Mr. Stoney's 

 paper, though read in 1867, was not published till 1869. 



Mr. Herbert Spencer, in his " First Principles" (pp. 532 to 535), 

 has also directed attention to the fact that the stars distributed 

 through space must tend, under the influence of gravity, to concen- 

 trate and become locally aggregated. Separate aggregations will be 

 drawn towards one another, and ultimately coalesce. The result 

 will be that the heat evolved by such collisions taking place under 

 the enormous velocities acquired by gravity must have the effect of 

 dissipating the matter of which they are composed into the gaseous 

 state. 



Both Mr. Stoney and Mr. Spencer consider the motions of the 

 cosmic masses to be due wholly to gravity, but, as we have seen, 

 gravity alone cannot account for the enormous amount of energy 

 originally possessed by the sun. 



