Graphometer
Encyclopedia
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
instrument used for angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
measurements. It consists of a semicircular limb divided into 180 degrees and sometimes subdivided into minutes. The limb is subtended by the diameter with two sight
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
s at its ends. In the middle of the diameter a "box and needle" (a compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
) is fixed. On the same middle the alidade with two other sights is fitted. The device is mounted on a staff via a ball and socket joint. In effect the device is a half-circumferentor
Circumferentor
A circumferentor, or surveyor's compass, is an instrument used in surveying to measure horizontal angles, now superseded by the theodolite. See also alidade....
. For convenience, sometimes another half-circle from 180 to 360 degrees may be graduated
Graduation (instrument)
-Linear graduation:Linear graduation of a scale occurs on a straight instrument. The graduation can identify linear measures, such as inches or millimetres on a rule. They can also be non-linear such as logarithmic or other transcendental scales....
in another line on the limb.
The form was introduced in Philippe Danfrie
Philippe Danfrie
Philippe Danfrie the elder , was a designer and maker of mathematical instruments in metal and paper, as well as a type-cutter, engraver, minter of coins and medals, publisher and author. Much is known about Danfrie's life and activities...
's, Déclaration de l’usage du graphomètre (Paris, 1597) and the term "graphometer" was popular with French geodesists. The preferable English-language terms were semicircle or semicircumferentors. Some 19th-century graphometers had telescopic
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
rather than open sights.
Usage
Plummet
Plummet is a American trance duo from Orlando, Florida. The act consists of producer/remixer Eric B. Muniz and female vocalist Cheramy Burgess....
at point C of the instrument. Align the diameter with leg KE of the angle using the sights at the ends of the diameter. Align the alidade with the leg KG using another pair of sights, and read the angle off the limb as marked by the alidade. Further uses of the graphometer are the same as those of the circumferentor.