32 FROM NEBULA TO NEBULA 



the moon itself does not obey the same law? Why does 

 it not? Is the test one of distance? or is it one of size? 

 If it is either of one or of the other, where is the line 

 of demarcation where body becomes planet or planet 

 body? 



Again, suppose instead of the moonlet we take a 

 hollow glass jrlobe filled with part sand and water, and 

 conceive it to be first thoroughly shaken each time, and 

 then successively held at the same heights previously 

 mentioned. Will or will not the sand settle to the bot- 

 tom of the vessel, that, is, toward the earth? Of course 

 it will so settle. 



Now, science says that the moon, and in fact all 

 the great heavenly bodies are, or were originally, in a 

 molten condition. Granting the fact, the moon's sub- 

 stance was therefore once in a fit state to permit the 

 precipitation of its heavier substances to the bottom, 

 (that is to say, the under half of the planet, not the 

 underneath surface) to wit, toward the earth-side, 

 where of course they must have remained when the body 

 cooled and hardened. 



Here, then, is the governing principle of axial rota- 

 tions : HEAVENLY BODIES ATTRACT EACH OTHER BY THEIR 



CENTERS OF GRAVITY, AND NOT BY THEIR CENTERS OF FORM. 



Planetary rotations may be divided into three 

 classes: (1) True or Tidal, (2) Negative, and (3) 

 Pseudo. 



The first class includes the earth, Mars, and prob- 

 ably Venus, of our system, and will be found explained 

 in a later chapter. 



The Negatives are Mercury, the moon, and all the 

 satellites generally. Their peculiarity consists in 

 always turning but one side toward their respective 

 primaries, for the matter of fact reason that they 



