[ 34 ° ] 
Received May 13, 1773. 
XXXVI. Properties of the Conic Sc Si ions ; 
deduced by a compendious Method. Being 
a Work of the late William Jones, FJq\ 
F. R. S. which he formerly communicated 
to Mr . John Robertfon, Libr. R. S. 
who now addrejfes it to the Revere?id Nevil 
Mafkdyne, F. R. S. AJlroimner Royal. 
S I R, 
Rend June 24, 
1 773 * 
O U well know that the curves 
formed by the fedtions of a cone, 
and therefore called Conic Sections, have, from 
the earlieft ages of geometry, engaged the attention 
of mathematicians, on account of their extenfive uti- 
lity in the folution of many problems, which were 
incapable of being conftrudted by any pcffible com- 
bination of right lines and circles, the magnitudes 
ufed in plane geometry. The properties of thefe 
curves are become far more interefting within the 
two laft centuries, fince they have been found to be 
fimMar to thofe which are deferibed by the motions 
of the cosleftial bodies in the Solar fyftem. 
Two 
