PHYSICAL EVOLUTION 7 



detect any common centre of gravity which holds 

 them in control. The stars have not yet attained 

 the regularity of movement that gravitation must 

 bring about in a very ancient system ; and this idea 

 of the comparative youth of the Universe is 

 strengthened when we remember that large numbers 

 of the primitive meteorites are still wandering in 

 space uncondensed into stars. If it be true that the 

 sun is one of the oldest stars in the Universe ; and if, 

 as geologists think, the earth is not more than a 

 hundred millions of years old, then it may very well 

 be that the creation of the cosmic dust out of which 

 the stellar universe has been formed, took place less 

 than two hundred millions of years ago. But, 

 although it may be possible to place a limit to the age 

 of the Universe, we can fix no time for its duration. 

 It is impossible to form an estimate of the hundreds 

 of millions of years that will pass before the end 

 approaches. Still, a time must come when all 

 energy will be equilibrated ; and when, possibly, the 

 visible Universe may resolve itself into invisible, 

 motionless ether. 



Evolution of the Solar System. In the Solar 

 System we can study the development of a meteoritic 

 swarm in greater detail. Here we find the whole 

 of the meteorites did not collect into a single mass, 

 but that several planets, as well as the sun, were 

 formed simultaneously. It has been shewn by 

 Professor G. H. Darwin that the effect of many 

 collisions among a swarm of meteorites would be to 

 gradually eliminate orbits of great eccentricity, until 

 in time a regular system would be developed, when 



