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.