CIRCUMFERENTOR

, a particular instrument used by surveyors for taking angles. It consists of a brass circle and index all of a piece; the diameter of the circle is commonly about 7 inches; the index about 14 inches long, and an inch and a half broad. On the circle is a card or compass, divided into 360 degrees; the meridian line of which answers to the middle of the breadth of the index. On the limb or circumference of the circle is soldered a brass ring; which, with another fitted with a glass, forms a kind of box for the needle, which is suspended on a pivot in the centre of the circle. There are also two sights to serew on, and slide up and down the index, as also a spangle and socket screwed on the under side of the circle, to receive the head of the three-legged staff.

To take, or observe the Quantity of an Angle by the Circumferentor. The angle proposed being EKG; place the instrument at K, with the flower-de-luce of the card towards you; then direct the sights to E, and observe what degrees are cut by the south end of the needle, which let be 295; then, turning the instrument about on its stand, direct the sights to G, noting again what degrees are cut by the south end of the needle, which suppose are 213. This done, subtract the less number from the greater, viz, 213 from 295, and the remainder, or 82 degrees, is the quantity of the angle EKG sought.