16 EVOLUTION 



enough, not merely to liquefy, but to scatter the material 

 of the colliders in incandescent gas over billions of miles 

 of space. Few stars travel at less than 20 miles a 

 second, and the conversion of this motion in the case 

 of such enormous masses into heat would be quite 

 enough. Most astronomers, however, do not think 

 collisions probable. They believe that the dead (or 

 faint) star ran into a dense and gigantic swarm of 

 meteorites, or even into a dark nebula ; or some internal 

 convulsion may have torn it open and scattered its 

 white-hot entrails over space. 



At all events, here was the birth of a nebula, and our 

 nebula and all those we see may have arisen in any one 

 of these ways. There is, in fact, no " beginning " to the 

 story of astronomical evolution. Some have said that, 

 as all the energy we know tends to be converted into 

 heat, there will come a time when all motion of 

 masses will cease, and so there must have been a time 

 when it began. But this assumes a knowledge on our 

 part of the cosmic machinery which we certainly do not 

 possess. Not until we have a fair command of the 

 ultimate sources of energy those strain-centres in ether 

 which finally make up the universe can we say whether 

 or no the heat is capable of being reconverted into energy 

 of movement. Astronomy points to no beginning or end, 

 and it is idle to speculate on a point that is wholly outside 

 the range of the scientist. Nebulae condense into solar 

 systems; dead stars return to nebular life. Mr. Gore 

 calculates that on the average probably two such 

 resurrections could be observed every year. 



For our purpose we start with the cloud of diffused 

 matter that once spread out far beyond the limits of our 

 solar system, and has slowly condensed into the spheres 

 that compose that system. We may take it to have 

 been initially a gas (like the new nebula in Perseus), and 



