THE LESSON or EVOLUTION 13 



cosmic dust is supposed to have aggregated into 

 meteorites, whose irregular movements were, in certain 

 places, reduced to order ; and so arose a number of 

 meteoritic streams, or swarms, moving through space. 

 Still under the force of gravitation, each of these 

 swarms got more and more dense, until, at last, 

 collisions took place between the meteorites ; light 

 and heat were given out, and the swarrn became a 

 nebula. The heat produced by the collisions would, 

 at first, be slight, but would gradually increase, until 

 the whole of the solid material was resolved into 

 vapour, and a star was formed. Concentration, how- 

 ever, would still go on, and the temperature of the 

 star would rise, until, in time, the loss by radiation 

 more than counterbalanced the gain by concentration, 

 when the star would begin to cool. At last light 

 would no longer be given off, and the star would end 

 by becoming a cold dark body moving in space. Of 

 course, some stars would attain a higher maximum 

 temperature than others ; and either a single or a 

 double star might be the result of the condensation ; 

 but all would follow a somewhat similar development. 

 Now, as a matter of fact, the spectroscope shows us 

 that stars in all these stages actually exist at the 

 present day in the heavens. In some the temperature 

 is increasing, in others it is decreasing ; and, although 

 small stars must run through their development 

 quicker than large ones, this is quite insufficient to 

 account for all the present differences. From which 

 it follows that some of the stars are much older than 

 others. The sun was amongst the earliest of formed 

 stars. When it was born, the sky must have presented 

 an almost uniform blackness. There was no Milky- 



