The Collaborative International Dictionary
Circumferentor \Cir*cum`fer*en"tor\, n. [See Circumfer.]
A surveying instrument, for taking horizontal angles and bearings; a surveyor's compass. It consists of a compass whose needle plays over a circle graduated to 360[deg], and of a horizontal brass bar at the ends of which are standards with narrow slits for sighting, supported on a tripod by a ball and socket joint.
A graduated wheel for measuring tires; a tire circle.
Wiktionary
n. (context surveying English) An instrument used to measure horizontal angles, consisting of a brass circle and an index, all of one piece.
Wikipedia
A circumferentor, or surveyor's compass, is an instrument used in surveying to measure horizontal angles. It was superseded by the theodolite in the early 19th century.
A circumferentor consists of a circular brass box containing a magnetic needle, which moves freely over a brass circle, or compass divided into 360 degrees. The needle is protected by a glass covering. A pair of sights is located on the North-South axis of the compass. Circumferentors were typically mounted on tripods and rotated on ball-and-socket joints.
Circumferentors were made throughout Europe, including in England, France, Italy, and Holland. By the early 19th century, Europeans preferred theodolites to circumferentors. However, the circumferentor remained in common use in mines and in wooded or uncleared areas, such as in America.
Usage examples of "circumferentor".
His father died when Jeremiah was twenty-two, a fairly miserable stretch beginning for him then, tho' he never drank enough to interfere with field-work, something he needed as much as ready access to Ale, still young enough to arise little inconvenienced after a night's strenuous drinking, having led till now the merry Life of a Journeyman Surveyor, errant all through the North country, one Great Land-Holding to another, three-legged Staff cock'd over his shoulder, Circumferentor slung in a Pitman's bag along with dry Stockings and a small wheaten Loaf, spare Needles and Pins, Plummets, Pencils, scrap-paper, and jeweler's Putty for the Compass, tho' Spaces not yet enclos'd would ever make him uneasy, not a promising mental condition for an outdoor job, oblig'd to cross the Fell now and again, a dangerous and frightening place, not only murderers abroad, but Spirits as well, and Spirits not necessarily in human form, no, the worst being, almost in human form, but not quite.
McClean takes over the eighteen-inch Hadley's, and Dixon repeats his Sights with the Circumferentor, obtaining at last an ungainly Oblique Triangle, from which they calculate Susquehanna to be about seven-eighths of a mile across.
Yet by now they can also both see the Western Mountains, ascending from the Horizon like a very close, hitherto unsuspected, second Moon, the Circumferentor daily tracking the slow rise in vertical angle to the tops of these other-worldly Peaks.