74 THE OCEAN. [Book HI. 



CHAPTER VI. 



THAT THE MOON's OEBITAL MOTION IS CAUSED BY 

 THE EAETh's KOTATION, AND ITS APPARENT LAG- 

 GING MOTION BY ASTRAL GRAVITATION. 



We have already observed that the idea of any 

 body having an innate tendency to move uniformly 

 forwards in a straight line is mere assumption. No 

 such innate tendency can, in the present state of know- 

 ledge, be demonstrated to exist in any known pheno- 

 mena. And we have shown that if any body really 

 has a tendency to move uniformly in a straight line, it 

 certainly is not in consequence of an innate property 

 of vis-inertise, because we have shown that its innate 

 property of vis-inertise constantly tends to bring it to 

 a state of rest : and therefore, if this tendency to move 

 uniformly in a straight line exist, it must be in con- 

 sequence of some force acting continuously with suffi- 

 cient power to overcome the vis-inertise of the body 

 set in motion. 



The cause of the moon's motion is a question 

 which has not hitherto been solved ; and we have 

 shown that the idea of the moon or any of the planets 

 having a tendency to continue to move uniformly 

 for wards in a straight line in consequence of an innate 



