Circumferentor

Circumferentor
Drawing of a circumferentor from the Cyclopaedia
Circumferentor with gunter's chain at Campus Martius Museum in Marietta, Ohio

A circumferentor, or surveyor's compass, is an instrument used in surveying to measure horizontal angles, now superseded by the theodolite. See also alidade.

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 a ball-and-socket joint for easy rotation.

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.

Contents

Usage

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°. Finally, subtract the lesser number, 182, from the greater, 296°; the remainder, 114°, is the number of degrees in the angle EKG.

If the remainder is more than 180 degrees, it must be subtracted from 360 degrees.

Surveying a region

To take the plot of a field, forest, park, etc, with a circumferentor, consider region ABCDEFGHK in Figure 2, an area to be surveyed.

  1. Placing the instrument at A, the fleur-de-lis towards you, direct the sights to B; where suppose the south end of the needle cuts 191°; and the ditch, wall, or hedge, measuring with a Gunter's chain, contains 10 chains, 75 links.
  2. Placing the instrument at B, direct the sights as before to C; the south end of the needle, e.g. will cut 279°; and the line BC contains 6 chains and 83 links.

Then move the instrument to C; turn the sights to measure D, and measure CD as before. In the same manner, proceed to D, E, F, G, H, and lastly to K; still noting the degrees of every bearing, or angle, and the distances of every side. This will result in a table of the following form:

Station Degrees Min. Chains Link
A 191 00 10 75
B 297 00 6 83
C 216 30 7 82
etc.

From this table, the field is to be plotted, or protracted.


Surveyor's double prism

Double prism as used in surveying.

A double prism is a device to measure right angles, consisting of two five sided prisms stacked on top of each other and a plumb-bob. it is used to stake out right angles, for example on a construction site.

See also

References


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Look at other dictionaries:

  • Circumferentor — Cir*cum fer*en tor, n. [See {Circumfer}.] [1913 Webster] 1. 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… …   The Collaborative International Dictionary of English

  • Circumferentor — Circumferentor, was Astrolabium; Circumferenz, der Kreisumfang …   Herders Conversations-Lexikon

  • circumferentor — /seuhr kum feuh ren teuhr/, n. Survey. an alidade equipped with a compass and two diametrically opposed vertical arms with slits for sighting through. [1600 10; < L circumferent(ia) CIRCUMFERENCE + OR2] * * * …   Universalium

  • circumferentor — noun An instrument used to measure horizontal angles, consisting of a brass circle and an index, all of one piece …   Wiktionary

  • circumferentor — cir·cum·fer·en·tor …   English syllables

  • circumferentor —   n. surveyor s angle measuring compass instrument …   Dictionary of difficult words

  • circumferentor — sə(r)ˈkəm(p)fəˌrentə(r) noun ( s) Etymology: Latin circumferentia circumference + English or 1. : a surveyor s compass with diametral projecting arms each carrying a vertical slit sight …   Useful english dictionary

  • Planchette — Plan chette , n. [F. See {Planchet}.] 1. A circumferentor. See {Circumferentor}. [1913 Webster] 2. A small tablet of wood supported on casters and having a pencil attached. The characters produced by the pencil on paper, while the hand rests on… …   The Collaborative International Dictionary of English

  • Graphometer — or semicircle is a surveying instrument used for angle measurements. It consists of a semicircular divided into 180 degrees and sometimes subdivided into minutes. The limb is subtended by the diameter with two sights at its ends. In the middle of …   Wikipedia

  • Azimuth compass — Compass Com pass (k[u^]m pas), n. [F. compas, fr. LL. compassus circle, prop., a stepping together; com + passus pace, step. See {Pace}, {Pass}.] 1. A passing round; circuit; circuitous course. [1913 Webster] They fetched a compass of seven day s …   The Collaborative International Dictionary of English

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