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A double-reflecting instrument for measuring angles, primarily altitudes of celestial bodies. As originally used, the term applied only to instruments having an arc of 60°, a sixth of a circle, from which the instrument derived its name. Such an instrument had a range of 120°. In modern practice the term applies to a similar instrument, regardless of its range, very few modern instruments being sextants in the original sense. Thus, an octant, having a range of 90°; a quintant, having a range of 144°; and a quadrant, having a range of 180°, may be called sextants. A marine sextant is designed primarily for marine navigation.

Related Terms

PLUNGER-TYPE INSTRUMENT

Moving-iron instrument in which the pointer is attached to a long and specially shaped piece of iron that is drawn into or moved out of a coil carrying the current to be measured.

PITOT TUBE

An instrument that measures the stagnation pressure of a flowing fluid, consisting of an open tube pointing into the fluid and connected to a pressure-indicating device. Also known as impact tube.

PIEZOMETER

1. An instrument for measuring fluid pressure, such as a gage attached to a pipe containing a gas or liquid. 2. An instrument for measuring the compressibility of materials, such as a vessel that determines the change in volume of a substance in response to hydrostatic pressure.

PHOTOCLINOMETER

A directional surveying light is directed through the material, and the instrument which records photographically the amount of light transmitted is measured with waves from the discharge.

PHONOGRAPH

[ENG ACOUS] An instrument for recording or reproducing acoustical signals, such as voice or music, by transmission of vibrations from or to a stylus that is in contact with a groove in a rotating disk.

PENETROMETER

1. An instrument that measures the penetrating power of a beam of xrays or other penetrating radiation. 2. An instrument used to determine the consistency of a material by measurement of the depth to which a standard needle penetrates into it under standard conditions.

PENDULUM LEVEL

A leveling instrument in which the line of sight is automatically kept horizontal by a built-in pendulum device (such as a horizontal arm and a plumb line at right angles to the arm).

PEDOMETER

1. An instrument for measuring and weighing a newborn child. 2. An instrument that registers the number of footsteps and distance covered in walking.

PANTOMETER

An instrument that measures all the angles necessary for determining distances and elevations.

PACHYMETER

An instrument used to measure the thickness of a material, for example, a sheet of paper.

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