THE ORIGIN OF THE EARTH 419 



own evolution is concerned. Now computations show that at the 

 stage -which marked the birth of Neptune, according to this hypoth- 

 esis, the moment of momentum of the nebula must have been 

 more than 200 times as great as the present moment of momentum 

 of the solar system; that at the stage of Jupiter's formation, the 

 moment of momentum must have been 140 times too great; that 

 at the Earth stage, it must have been 1,800 times too great; and 

 so on. Here is not only an enormous discrepancy, but one that 

 varies greatly and irregularly from stage to stage. 



8. If the masses of the planets are compared with the moments 

 of momenta they carried off from the parent nebula, strange 

 discrepancies are disclosed. The matter in the ring supposed to 

 have formed Jupiter and his moons had a mass less than one- 

 thousandth of that of the nebula at the time of its separation; 

 but Jupiter and his moons now have about 95 per cent of the total 

 moment of momentum which the nebula then had. The Laplacian 

 hypothesis thus calls on us to believe that an equatorial ring having 

 a mass less than a thousandth of the mass of the parent body, car- 

 ried off in its separation 95 per cent of the total moment of momen- 

 tum. The supposed separation of other rings involves similar 

 incredible ratios. 



9. Under the Laplacian hypothesis, the satellites should all 

 revolve about their planets in the direction in which the planets 

 rotate on their axes; but the recently discovered ninth satellite 

 of Saturn revolves m the opposite direction. 



10. Though our knowledge of nebulae has been extended 

 greatly in recent years, nebulae with such rings as the Lapla- 

 cian theory postulates have not been found. The larger number 

 of those at first supposed to support the theory have been found 

 by improved methods of research to be spiral nebulas or anoma- 

 lous forms. 



II. The Meteoritic Hypotheses 



It was long ago noted that shooting stars entered the upper 

 atmosphere nightly in great numbers, and that occasionally frag- 

 ments of stony and metallic matter fall from the heavens. Out of 

 this grew the notion that the earth may have been built up in this 

 way, save that the process was more rapid in the early ages of the 



