MAN FROM THE FARTHEST PAST 
spectrum appearances which we have named. But now, 
from the rarity of a red star newly born, it grows old and 
ends as a red star, indeed, but with a density approach- 
ing or even exceeding that of the solid metals such as iron. 
Finally failing altogether to supply glowing heat, the star 
becomes dark, as indeed many great celestial bodies are 
known to be. These reveal their presence not by their 
light but by their gravitation or by cutting off the light of 
companion stars. 
Such, it appears, is the evolution of a galaxy and a star. 
A solar system presents another operation. Among the 
multitudes of stars, all of which are in rapid motion in 
various directions, there will be some pairs, in the course of 
billions or trillions of years, which will approach so closely 
together as nearly to collide. Though not actually pre- 
senting the tremendous catastrophe of collision, which 
between two bodies so enormous would indeed be beyond 
description, a pair of stars passing near each other would 
raise such great mutual tides that their material would not 
merely swell out like our ocean tides, but for a time would 
actually flow away in ropelike streams into space by 
reason of the adventure. Such material, after the passage 
of the disturbing star, would collect into planets; and such, 
we may imagine, is the origin of our solar system. 
We are to suppose, then, that our earth was formed by 
the gathering together of matter which had been caused to 
flow out from the sun by reason of the close approach, ages 
ago, of some other star. As the stars often exceed twenty- 
five miles a second in their mutual approach or recession, 
and as we have noted that the nearest star, Alpha Cen- 
tauri, is only some 25,000,000,000,000 miles away, it is 
conceivable that the near catastrophe which gave birth to 
our earth might have happened no more than 1,000,000,- 
000,000 seconds, or 30,000 years ago. But as our radium 
clock has told us that the earth’s crust is fully a billion 
years old, we must conclude that it was not the nearest of 
the stars but some unknown one, now very distant, which 
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