A Circumferentor, Or Surveyor's Compass, Is an Instrument Used in Surveying to Measure Horizontal Angles, Now Superseded by the Theodolite
1.) CIRCUMFERENTOR Description: A circumferentor, or surveyor's compass, is an instrument used in surveying to measure horizontal angles, now superseded by the theodolite. It consists of a brass circle and an index, all of one piece. On the circle is a card, or compass, divided into 360 degrees; the meridian line of which is in the middle of the breadth of the index. On the circumference of the circle is a brass ring, which, with another ring fitted with glass, make a kind of box for the needle, which is suspended on a rivet in the center of the circle. On each extreme of the index is a sight. The whole apparatus is mounted on a staff, with aball-and-socket joint for easy rotation. Brief History: Circumferentors were made throughout Europe, including England, France, Italy, and Holland. By the early 19th century, Europeans preferred theodolites to circumferentors. However, in America, and other wooded or uncleared areas, the circumferentor was still in common use. Usage/ Operations: Figure 1: Angle EKG Figure 2: Region ABCDEFGHK -Measuring angles To measure an angle with a circumferentor, such as angle EKG (Figure 1), place the instrument at K, with the fleur-de-lis in the card towards you. Then direct the sights, until through them you see E; and note the degree pointed at by the south end of the needle, such as 296°. Then, turn the instrument around, with the fleur-de-lis still towards you, and direct the sights to G; note the degree at which the south end of the needle point, such as 182°.
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