A Forecast of the End 123 



birth and death of worlds. There is still a good deal of 

 divergence in the different systems of classification (as 

 in zoology), but the main line of evolution is clear. 

 From white stars at the highest temperature we descend 

 slowly to blood-red stars with choking fires. The 

 intermediate stages are difficult to deal with, as they 

 may be either rising or falling. But there are 

 unmistakable classes of dark red stars, in which the 

 broad dark absorbent lines of the spectrum show the 

 deepening of the cooler vaporous envelope round the 

 star. Red variable stars seem to carry the story a step 

 further. Apart from cases of variable stars in which a 

 star probably passes periodically through a swarm of 

 meteors, there seem to be others in which the molten 

 mass is making its last struggle with the dark envelope 

 that is closing on it, and bursting out occasionally with 

 fiery energy. Beyond this are the almost dark, and then 

 entirely dark, companions of some of the stars. It is 

 not difficult to follow the evolution. As the energy of 

 the central mass decreases, the cooler vapour forms a 

 deeper layer round it until at last the whole sinks to a 

 mass of dull red-hot metal and gas. The vapours grow 

 colder, and run to liquid. Colder still, the formation of 

 solid matter sets in, and there will be the long struggle 

 of the first formation of crust. In the end the com- 

 paratively exhausted sun can resist no further, and the 

 band of rock encircles it, only to be burst by great 

 volcanic rushes through its crevices. 



That this is the future evolution of our sun is taught 

 us beyond question by the whole contents of astronomy 

 and the early chapters of geology, to say nothing of 

 physical principles. Slowly, in some future age, as 

 humanity builds its glittering towers in the happier 

 cities to come, the life-giving energy of the sun will fail. 

 By what mechanical devices the failure of light and 



