To return upon a Tract you have just before mov’d on.
For
Example
, if you have mov’d from the lower end of the
Room
, to the upper end, and have a mind to return upon the same
Tract
, as the
Tract
mark’d A, you must remove, and place the
Line
or
Tract
, on which you would return, on one side or the other, as you shall find most convenient, as is mark’d by the Letter B, and which in effect is the same with the foregoing; which two
Tracts
must be join’d together by a pointed
Line
mark’d C, which only serves to conduct the Sight from one
Line
to the other.
The same thing must be observ’d in moving several times round on the same Circle, as upon the Circle mark’d D; about which may be describ’d as many Circles as shall be necessary. As for Example, the Circles E and F, which must be supposed to be on the same Circle with the Circle D.