THE COMPLEXITY OF NATURE. 125 



But, as observation shows, the contrary has taken place, 

 since, besides its movements of diurnal rotation and annual 

 revolution, the earth has its mobile axis, which is indepen- 

 dently inclined and displaced. Thus, the material molecules 

 of the planetary surface are not all at an equal distance 

 from the centre; and, consequently, the earth is not a 

 perfect sphere. It is, as D'Alembert has demonstrated, 

 the bulging, equatorial portion which experiences, owing 

 to the solar attraction, a retrograde movement, carrying 

 onward the rest of the globe in a general march, called the 

 precession of the equinoxes. 



But this general movement, as we have seen, is, in itself, 

 simply the mean of a series of oscillations, which D'Alem- 

 bert has also connected with gravitation. He has shown 

 that the nutation of the earth's axis results from the moon's 

 attraction on the bulging portion of our globe. Finally, it 

 has been mathematically demonstrated that the said bulging 

 portion of the earth produces, under the continuous action 

 of the sun, the precession of the equinoxes ; just as this 

 portion determines, by its continuous action, the nutation 

 of the lunar axis. As in this universal ponderation all the 

 wheelwork of the world catches (tons les rouages du monde 

 s* engrenenf), and the planets, such as Mars and Venus, must 

 also have their share in the action, however weak it may 

 be, we have contrived to render an exact account of the 

 slow changes of the obliquity of the Ecliptic. 



Let us resume. Movement and matter, all is ponderated. 



Inasmuch as matter is unequally distributed around the 



