402 HISTORY OF PHYSICAL ASTRONOMY. 



went before." This was written, however, under the influence of some 

 degree of mistake ; and in a subsequent letter, Newton says, " Now I 

 understand he was in some respects misrepresented to me, I wish I 

 had spared the postscript to my last," in which is the passage just 

 quoted. We see, by the melting away of rival claims, the undivided 

 honor which belongs to Newton, as the real discoverer of the proposi- 

 tion now under notice. We may add, that in the sequel of the third 

 Section of the Principia, he has traced its consequences, and solved 

 various problems flowing from it with his usual fertility and beauty of 

 mathematical resource ; and has there shown the necessary connection 

 of Kepler's third law with his first and second. 



3. Moon's Gravity to the Earth. — Though others had considered 

 cosmical forces as governed by the general laws of motion, it does not 

 appear that they had identified such forces with the force of terrestrial 

 gravity. This step in Newton's discoveries has generally been the 

 most spoken of by superficial thinkers ; and a false kind of interest 

 has been attached to it, from the story of its being suggested by the 

 fall of an apple. The popular mind is caught by the character of an 

 eventful narrative which the anecdote gives to this occurrence ; and 

 by the antithesis which makes a profound theory appear the result of 

 a trivial accident. How inappropriate is such a view of the matter 

 we shall soon see. The narrative of the progress of Newton's thoughts, 

 is given by Pemberton (who had it from Newton himself) in his pre- 

 face to his View of Newton's Philoso})hy, and by Voltaire, who hai it 

 from Mrs. Conduit, Newton's niece. 5 " The first thoughts," we are 

 told, " which gave rise to his Principia, he had when he retired from 

 Cambridge, in 1666, on account of the plague (he was then twenty- 

 four years of age). As he sat alone in a garden, he fell into a specu- 

 lation on the power of gravity ; that as this power is not found sensi- 

 bly diminished at the remotest distance from the centre of the earth 

 to which we can rise, neither at the tops of the loftiest buildings, nor 

 even on the summits of the highest mountains, it appeared to him 

 reasonable to conclude that this power must extend much further than 

 was usually thought : Why not as high as the moon ? said he to him- 

 self; and if so, her motion must be influenced by it; perhaps she is 

 retained in her orbit thereby." 



The thought of cosmical gravitation was thus distinctly brought 

 into being ; and Newton's superiority here was, that he conceived the 



6 EUmens de Phil, de Newton, 3me partie, chap. iii. 



