530 POPULAR LECTURES AND ;l/)J)KESSES. 



implied in Kepler's laws of the motions of the 

 Planets and of the Moon were frequent subjects of 

 discussion at its regular meetings and at perhaps 

 even more important non-official conferences among 

 its fellows. 



In 1684 the Senior Secretary of the Royal 

 Society, Dr. Halley, went to Cambridge to consult 

 Mr. Newton on the subject of the production of 

 the elliptic motion of the Planets by a central 

 force, 1 and on the loth of December of that year 

 he announced to the Royal Society that he " had 

 seen Mr. Newton's book, De Motu Corporum? 

 Some time later, Halley was requested to " remind 

 Mr. Newton of his promise to enter an account of 

 his discoveries in the register of the Society," with 

 the result that the great work Philosophic 

 Naturalis Principia MatJiematica was dedicated 

 to the Royal Society, was actually presented in 

 manuscript, and was communicated at an ordinary 

 meeting of the Society on the 28th of April, 1686, 

 by Dr. Vincent. In acknowledgment, it was 

 ordered " that a letter of thanks be written to Mr. 



1 Whewell's History of the Inductive Sciences, vol. 2, p. 77. 



