( 1^0 ) 
to be carried over given Curve Lines, and the third 
defcribes the Locus required. 
Let the Right Lines CQ, SN,DN, revolve a- 
bout the Poles C, S, D, where that which revolves 
about D, ferves to guide the Motion of the other 
two ; its Interfe&ion with C Q_ moving over the 
Curve G Q, while its Interfe&ion with S N moves 
over the Curve F N. Suppofe that the Right Line B b 
touches the Curve G in CL, and that the Right 
Line A a touches the Curve F N in N. In order 
to draw a Tangent to the Locus of P ; join D C, 
DS and C S, and conftitute the Angle D Q.R, 
equal to C Q_B, fo that Q_R lie the contrary way 
from Q^D that Q^B lies from Q_C, and let QJR 
meet D C in R. Conftitute alfo the Angle D N T, 
equal to S N A with the like precaution, and let 
N T meet D S in T. Join R T, and produce it till 
it meet C S in H ; then join P H, and make the 
Angle C P L equal to S P H, fo that P L and P H, 
may lie contrary ways from C P and S P; and P L 
ftxall be a Tangent at P, to the Locus described by 
P, the Iuterfedion of C Qjtnd S N. 
I have 
