< 12 j 4 ) 
On the under fide of tlnis Rular ( the fide from the 
Eye in the Scheme ~) let there be pinn’cf or glevvcd a little 
piece of Wood ( In the form of a Quadrant, the part 
which is feeti being marked kl~) whole edge ( or limb ) 
l{ /, is an arch of a Circle of Center ( i, ) and Radius i h 
( the fame with the little Wheel. ) The defign of- this 
piece of Wood is, that in the feveral Politions of the 
Rular E F, the circular Limb k l always touching and 
Hiding by the edge of the Rular A B, the Center of the 
■Wheel may be always in a line ( * » ) parallel to the 
Rular A B. 
In the Rular CD make M B = il or i k r and at M 
fallen a little Pin, and another to the Rular EF near the 
Wheel, a9 at p • To thele two Pins let be faftned the two 
ends of a String M R, fo that its whole length ( from 
Pin to Pin ) 4- p i, be equal to the intended Axis of the 
Curve T W; 
The Inftrument being thus prepar’d, let a ftrong Rular 
SO, be faftned ( or held fall ) upon the Paper or Plain 
that the Curve is to be drawn upon. Lay the Rular E F 
from M towards A, and parallel to A.B, fo that the String 
lye all ftraight along the edge of the Rular E F from M top, 
the point Sk. of the Quadrantal piece of Wood reding up- 
on the edge of the Rular A B» Then with a final 1 Pin at 
M keeping the String- dole to the edge of the Rular E F, 
and with your other hand upon the end E, keeping the 
Wheel tight to the Paper or Plain, move the Pin, String 
and Rular E F from M towards O, the Rular C D Aiding 
along by the faftned Rular S O in a right .line, the 
Wheel g h will by its motion defcribe the dcfired Curve 
1 TV. ‘ " 
