( 1 6 Z ) 
cording to any Power of the Diflance, then the Den- 
fity of the Medium in any place, is reciprocally 
proportional to the Tangent of the Curve at that 
place, bounded at one Extremity by the Point of 
Contact, and, at the other, by its Interfe&ion with 
a Perpendicular raifed at the Center of the Forces to 
the Ray drawn from that Center to the Point of 
Conrad. Let A L be the Curve defcribed by a 
Force directed to the Point S ; let L T touch the 
Curve at L, andraife S T per- 
pendicular to S L, meeting L T 
in T, and the Denfity in L 
lhall be univerfely as L T, if 
the Refiftance be fuppofed to 
obferve the compound Pro- 
portion of the Denfity, and of 
the Square of the Velocity. 
Befides what I have obfcrved here, I propofe to 
iliuftrate and improve feveral other Parts of the 
Treatife concerning the Defcription of Curve Lines 
in this Supplement. 
That Treatife requires thefe Additions and Illuftra- 
tions the more, that tho* the whole almoft was new, 
it was publifhed in a hurry, when I was very young, 
before I had time to confider fufficiently which were 
the beft ways of demonftrating the Theorems, or re- 
folding the Problems, for which this Supplement I 
hope, will make fome Apology. 
N. B. The following Taper , dated at Nancy, 
Novem. 27, ijizfis that which the Author 
mentions in his Letter . 
SECTIO 
