156 FROM NEBULA TO NEBULA 



4. Why the earth's axis remains fixed. 



5. The fundamental significance of Kepler's laws. 

 (>. The logical basis for the "conservation of mo- 

 ment of momentum." 



7. The secret of centrifugal motion, and why it 

 so exactly counterbalances the centripetal. 



S. Dispenses' witli projectile planetary motions, 

 so that we are relieved from discovering their origin. 



!). It renders purely academic the question of the 

 existence of a resisting medium. 



10. It explains why the planets and their satel- 

 lites revolve and rotate in the same direction. 



11. It gives a sound reason why the planets re- 

 volve in approximately circular orbits, and why they 

 naturally gravitate toward a common plane. 



12.. Why Phonos' period of revolution is not log- 

 ically dependent on Mars' period of rotation. 



SUB PRINCIPLE II. Heavenly bodies attract each 

 other, not by their centers of figure but by their 

 centers of nia>ss (that is, of gravity}. 



This principle when combined with sub principle' I 

 explains 



1. Tides by depression. 



The axial rotation of the earth and of Mars. 



3. The staring attitude of Mercury, the moon, 

 etc., with reference to their respective primaries. 



4. The psendo rotation of the sun and of the major 

 planets. 



5. The sun's and Jupiter's equatorial acceleration. 



6. The moon's libratiou. 



7 Why "Tidal Evolution" is impossible. 



8. Why the earth's day has not been lengthened 

 by "tidal retardation." 



