96 The Realm of Nature CHAP. 



continuing to contract and to spin more rapidly threw off 

 another ring which gave rise to Uranus, and so on with the 

 other planets, which themselves by a similar process threw 

 off rings to persist like those of Saturn or to condense into 

 satellites. The ring thrown off after the formation of 

 Jupiter, instead of condensing into one planet, consolidated, 

 perhaps on account of perturbation by its great neighbour, 

 into separate bodies the asteroids. The residue of the 

 original nebula remained as the great globe of the Sun. 



144. Meteoritic Hypothesis. Recently Norman Lock- 

 yer has pieced together the facts discovered by modern astron- 

 omers, and he believes them to countenance the theory that 

 originally all space was filled with matter in its simplest 

 or primary form, that this matter commenced to aggregate 

 under the influence of gravity and chemical affinity, produc- 

 ing a fine moving dust of the elements and latterly of their 

 compounds. This dust further condensed and gave rise to 

 meteorites in great moving swarms separated by tracts of 

 empty space. As the meteoritic swarms shrank by gravity, 

 collisions between the individual meteorites became more 

 frequent, and some of their energy of motion was changed 

 to heat which partly vaporised them, giving rise to the bodies 

 we recognise as nebulas or as variable stars. These swarms 

 of moving meteorites present many of the properties of a 

 gas on a very large scale, and the motion and equilibrium 

 of a meteoritic nebula would be very similar to those of a 

 gaseous one. Meteoritic material is supposed to pass from 

 the nebular state into that of separate and much denser 

 suns surrounded by families of planets somewhat in the 

 manner Laplace suggested. Lockyer differs from Laplace 

 in making gravitation and molecular attraction the primary 

 cause rather than heat, and so including in the theory the 

 heating up as well as the cooling down of the Universe. 



BOOKS OF REFERENCE 



J. Stuart, A Chapter of Science, S.P.C.K. (A thoroughly 

 scientific and attractively simple explanation of the movements of 

 th'e solar system. ) 



