PROBA BLE ORIGIN OF NEB UI . K. 3 1 5 



which is to endure for millions of years, and to form 

 the centre of a planetary system like our own, that fche 

 masses coming into collision should be converted into 

 an incandescent nebulous mass. But the greater the 

 amount of motion left unconverted into heat, the less 

 is the chance of this condition being attained. A 

 concussion which would leave the greater part of the 

 motion of translation untransformed, would be likely 

 as a general rule to produce merely a temporary star, 

 which would blaze forth for a few years, or a few 

 hundred years, or perhaps a few thousand years and 

 then die out. In fact we have had several good 

 examples of such since the time of Hipparchus. Now, 

 although it may be true that, according to the law of 

 chances, collisions producing temporary stars must be 

 far more numerous than those resulting in the forma- 

 tion of permanent stars, nevertheless the number of 

 those temporary stars observable in the heavens may 

 be perfectly insignificant in comparison with the num- 

 ber of permanent stars. Suppose there were as many 

 as one hundred temporary stars formed for one 

 permanent, and that on an average each should continue 

 visible for 1000 years, there would not at the present 

 moment be over half-a-dozen of such stars visible in 

 the heavens. 



4th. " Such collisions as the theory assumes are 

 wholly hypothetical ; it is extremely improbable that 

 two cosmical bodies should move in the same straight 

 line ; and of two moving in different lines, it is impro- 

 bable that either should impinge against the other." 

 I reply, if there are stellar masses moving in all 

 directions, collisions are unavoidable. It is true they 

 will be of rare occurrence ; but it is well that it is so ; 

 for if they had been frequent the universe would be in 

 a blaze, and its store of energy soon converted into 

 heat. 



