24 EVOLUTION 



should find that sixty million years would be con- 

 sumed in this portion of evolutionary history. The 

 true period must be much greater, and it does not 

 seem unreasonable to suppose that 500 to 1,000 

 million years may have elapsed since the birth of the 

 moon." 



The point is of little importance, though it has a 

 fascination for many people, and we will pass on to the 

 second subject that it is proper to touch upon before we 

 take up again the chief thread of our story. We have 

 seen, in outline, the birth of our solar system from a 

 nebula. To what extent may we apply that scheme to 

 the other suns of our stellar universe ? 



That the " stars " are " suns" now needs no emphasis. 

 The same elements, in greater or less number, in one or 

 other form, enter into their composition. Some are 

 smaller, some thousands of times larger (or its equiva- 

 lent in brilliancy) than our sun. More than a hundred 

 million of them make up the system to which our sun 

 belongs. Those we can examine are travelling at an 

 average rate of 21 miles a second ; a few of them at 100, 

 150, and even 250 miles a second. Few of them ap- 

 proach within 100 billion miles of us. The greater 

 number are more than 1,000 billion miles away, and 

 elude the wonderful measuring devices of the astronomer. 

 Millions lie so far away that, though they are doubtless 

 comparable to ours in size and brilliancy (150 times as 

 brilliant as the lime in the limelight, and many of them 

 much more intense), they take seven or eight hours to 

 register a faint point of light on the most sensitive 

 photographic plate in the larger telescopes. Hour after 

 hour their waves of light are falling on the plate at the 

 rate of 700 billion per second, yet they take so long to 

 impress a tiny dot on a plate that would register a land- 

 scape in a fiftieth of a second. 



