A Forecast of the End 121 



On the other hand, any speculative student who does 

 not care to sacrifice altogether these harrowing possibili- 

 ties may be assured that we really have no guarantee of 

 the stability of our system for a single year. All the 

 stars are moving rapidly, but they seem generally to 

 move in considerate orbits and keep their distances from 

 each other. The nearest to us is twenty-five billion 

 miles away. Now that we know of the existence of dark 

 stars, no one can say how much nearer we are to one of 

 these. Most probably the dark stars are regulated in 

 their paths by gravitation, like the visible ones, but the 

 paths of the stars are still very obscure, and we saw that 

 some astronomers believe in collisions, or close and 

 mischievous approaches. In fine, there are the dark 

 nebulae and heavy swarms of meteorites which very 

 many astronomers regard as the causes of the conflagra- 

 tions that are witnessed occasionally in the heavens. 

 No astronomer could give us any security whatever that 

 we may not at any time plunge into one of these, as our 

 sun bears us through space at a speed of twelve miles 

 per second. Those who revel in lurid possibilities may 

 dwell on this. For most of us it is enough that our 

 solar system has escaped such contingencies for some 

 hundreds of millions of years, and may be trusted to do 

 so for the few million years that still lie before 

 humanity. 



I will not linger over the further possibilities that have 

 been suggested by ingenious writers. Geologists have 

 pointed out that the sea and rain are wearing away the 

 land, and conjured up visions of a time when the ocean 

 may once again flow over the entire earth. No doubt 

 that would be the natural line of development in an 

 indefinite time, but it happens that the power of man to 

 protect his land is equally developing. 



Physicists point out that the gases of our atmosphere 



