GRAVITATION VERSUS INERTIA 23 



But how do we know that this movement is gravi- 

 tational? 1 



Obviously the first answer to this is, that the bur- 

 den is on the other side to prove that it is not of th'at 

 character. Newton proved what gravitation can do- 

 that it is a force, that it acts uniformly according to 

 a settled law and in the absence of proof of some other 

 adequate agency we are bound to assume that which is 

 already established. The second answer is, that falling 

 bodies lower their center of gravity in the direction of 

 fall. If it be true that the sun is falling by gravity, 

 so must the earth be; and on turning to it, behold, its 

 continents nre preponderatingly settled toward the 

 north and its waters relegated to the south, showing 

 that the earth has a bottom and that that bottom hangs 

 downward toward the north star. The only other planet 

 that is enough like the earth to serve as a criterion of 

 the same fact is Mars, and see, he too shows by his 

 permanent northern snow-cap (the southern disappears 

 every season) that his heavier or land end lies in that 

 direction. Third. The axes of the earth and Mars lie 

 almost if not quite parallel, indicating as by a com- 

 pass the direction of the gravitational pull. Fourth. 

 Perhaps, however, the most telling proof of all, since 

 it is apparently so isolated, is that of the acceleration 

 of the moon's mean motion, to which reference has 

 already been made. Of this Dr. Young says : 2 



1 Modern science assumes this motion, also, to be projectile. Is 

 it not wonderfully illuminating- to learn that although a bullet can 

 be shot in only one direction at a time, a planet can be projected in at 

 least two ways, and probably in as many more as the exigencies of 

 science may require? Newton postulated that the moon was projected 

 tangentially along the plane of her orbit, which he assumed to Tbe fixed 

 In space; but here we have another projection that he knew not of, 

 at nearly a rig-ht ang-le to the first! It speaks marvels for the elas- 

 ticity of his demonstration that he could omit a factor like this new 

 motion, and yet come out right in his result! Or is it that the faith 

 of modern science so far surpasses that of the prophets and martyrs 

 of old? Or have planets perhaps astral bodies and bifurcated tra- 

 jectories? 



2 General Astronomy, Page 301. 



