C 75 1 
“ Which is, T^hat the hod\\ in fiich a cafe^ will 
defcribe^ by lines drawn from the two Jixed points, 
“ equal folids in equal times, about the line joining the 
“ faid fixed points. 
And (after obferving that Sir Ifaac Newton has 
proved, that Kepler’s law of bodies defcribing equal 
areas in equal times about the centers of their revo- 
lution, cannot hold, whenever the body has a gravity 
or force to any other than one and the fame point) 
further fays, “ there feems to be wanting fome fuch 
“ law as I have here laid down, that may ferve to 
“ explain the motions of the Moon and Satellites, 
“ which have a gravity towards two different centers.” 
About the year 1742, difcourfing with that emi- 
nent mathematician, the late William Jones, Efq; 
F. R. S- on the above-mentioned law, he fliewed me 
itsdemonflration, and permitted me to take a copy 
thereof; and as I conceive it to be highly worth pre- 
ferving, I now offer it to your confideration, about 
giving it a place in the Philofophical Tranfadlions. 
1 am, 
S I R, 
Your mod humble fervant. 
February 27, 
1769. 
J. Robertfon. 
