CHAPTER XX. 



THE MOVEMENTS OF THE EARTH. 



It has been shown in the preceding pages that the 

 waters of the earth are in a state of constant circulation ; 

 that the atmosphere is never in repose; that the soHd 

 materials of the earth's crust are slowly but incessantly- 

 changing their position ; and that the matter of the organic 

 world is subject, in a yet more marked degree, to cychcal 

 changes. Absolute repose is, indeed, a state utterly 

 unknown upon the earth's surface. Nor is the globe itself 

 exempt from movements which are of a still grander kind. 

 The huge ball which was described in the last chapter is 

 constantly in motion. Part of this motion is a move- 

 ment of rotation, whereby the earth is perpetually spinning 

 round like a top ; and part is a movement of revolution, 

 whereby it progresses through space, and is carried round 

 the sun. 



If the earth were fixed in space, without either of these 

 motions, it is plain that the half which happened to be 

 turned towards the sun would enjoy uninterrupted sunshine, 

 while the opposite half would be plunged in permanent 

 shadow; in other words, perpetual day would reign in 

 one half, and perpetual night in the other half The 



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