236 THE BORDERLAND OF SCIENCE. 



must have cooled more rapidly than the earth; and 

 the time must at length have arrived when the moon 

 had become an opaque orb, while the earth on which 

 we live was still a sun. Even at this early stage of 

 our existence the moon must have so rotated as to 

 turn the same face towards the earth's then glowing 

 orb. 



But now a circumstance has to be considered which, 

 startling though it may seem at first, is yet consistent 

 with what has been ascertained respecting the sun and 

 other bodies. There is a great mass of evidence tending 

 to show that our sun expels matter from his interior 

 with a velocity sufficient to carry such matter entirely 

 away from him. This has been shown by the micro- 

 scopic and chemical structure of meteorites, by their 

 paths and rates of motion, and by many circumstances 

 which will be found detailed at length in the article 

 called ' Meteors, seed-bearing and otherwise,' in the 

 present volume. It is also very strikingly supported 

 by the behaviour of the so-called eruption-prominences 

 of the sun. Passing from the sun to the major planets 

 which even now seem to have some of the qualities 

 of subordinate or secondary suns, and must certainly 

 have been such long after the earth and her fellow 

 minor planets had cooled down into the condition 

 of habitable worlds we find very striking evidence 

 to show that these minor suns or major planets 

 erupted from their interior the material of meteor 

 systems and of those comets of small period which 

 have been called the comet-families of the major 



