an instrument used by surveyors for taking angles.

It consists of a brass index and circle, all of a piece. The index is commonly about 14 inches long, and an inch and a half broad; the diameter of the circle is about seven inches. On this circle is made a chart, whose meridian line answers to the middle of the breadth of the index, and is divided into 360 degrees. There is a brass ring foldered on the circumference of the circle, on which screws another ring, with a flat glass in it, so as to form a kind of box for the needle, suspended on the pivot in the centre of the circle. Circumflex circle. There are also two sights to screw on, and slide up and down the index; as also a spindle and socket screwed on the back side of the circle for putting the head of the staff in.

How to observe the Quantity of an Angle by the Circumferentor. Let it be required to find the quantity of the angle EKG; first place your instrument at K, with the flower-de-luce of the chart towards you; then direct your sights to E, and observe what degrees are cut by the fourth end of the needle, which let be 296; then, turning the instrument about, direct your sights to G, noting then also what degrees are cut by the fourth end of the needle, which suppose 247. This done, always subtract the lesser from the greater, as in this example, 247 from 296, the remainder is 49 degrees, which is the true quantity of the angle EKG.