COSMIC PHILOSOPHY 



and that larger gyration which, in the case of 

 the earth, causes the precession of the equi- 

 noxes. 



" These rhythms, already more or less com- 

 pound, are compounded with each other. Such 

 an instance as the secular acceleration and re- 

 tardation of the moon, consequent on the vary- 

 ing eccentricity of the earth's orbit, is one of 

 the simplest. Another, having more important 

 consequences, results from the changing direc- 

 tion of the axes of rotation in planets whose 

 orbits are decidedly eccentric. Every planet, 

 during a certain long period, presents more of 

 its northern than of its southern hemisphere to 

 the sun at the time of its nearest approach to 

 him ; and then again, during a like period, pre- 

 sents more of its southern hemisphere than of 

 its northern — a recurring coincidence which, 

 though causing in some planets no sensible al- 

 terations of climate, involves in the case of the 

 earth an epoch of 21,000 years, during which 

 each hemisphere goes through a cycle of tem- 

 perate seasons, and seasons that are extreme in 

 their heat and cold. Nor is this all. There is 

 even a variation of this variation. For the 

 summers and winters of the whole earth be- 

 come more or less strongly contrasted, as the 

 eccentricity of its orbit increases and decreases. 

 Hence during increase of the eccentricity, the 

 epochs of moderately contrasted seasons and 

 172 



