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A pair of propellers on concentric shafts, turning in opposite directions.

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An imaginary sphere of infinite radius concentric with the earth, on which all celestial bodies except the earth are imagined to be projected


A transmission cable consisting of two concentric conductors insulated from each other


Having the same center.


Paper ruled with lines to aid in the plotting of coordinates. In its most common form, it has two sets of parallel lines, usually at right angles to each other, when it is also called CROSS- SECTION PAPER. A type ruled with two sets of mutually-perpendicular, parallel lines spaced according to the logarithms of consec- utive numbers is called logarithmic coordinate papa or semilogarithmic coordinate paper as both or only one set of lines is spaced logarithmically. A type ruled with concentric circles and radial lines from the common center is called polar coordinate paper. Also called GRAPH PAPER.


Circles concentric to the center of a formation of ships, designated by their radii in thousands of yards.


A modification of the Lambert conformal projection for use in polar regions, one of the standard parallels being at latitude 89°59'58' and the other at latitude 71° or 74°, and the parallels being expanded slightly to form complete concentric circles. Also called NEY’S MAP PROJECTION.


A device used in conjunction with a plotting sheet having equally spaced concentric circles (range circles) drawn about two or more stations of a radio determination system being operated in the ranging mode.


One of a set of equally spaced concentric rings, centered on own ship’s position, providing a visual presentation of range on a radar display.


  1. A curved surface all points of which are equidistant from a fixed point within, called the center. The celestial sphere is an imaginary sphere of infinite radius concentric with the earth, on which all celestial bodies except the earth are imagined to be projected. The celestial sphere as it appears to an observer at the equator, where celestial bodies appear to rise vertically above the horizon, is called a right sphere; at the pole, where bodies appear to move parallel to the horizon, it is called a parallel sphere; between the equator and pole, where bodies appear to rise obliquely to the horizon, it is called an oblique sphere. Half a sphere is called a HEMISPHERE. 2. A body or the space bounded by a spherical surface. For most practical problems of navigation, the earth is considered a sphere, called the terrestrial sphere.


A device for separating components of a liquid solution, consisting of a series of perforated concentric rings in a cylindrical drum that rotates at 2000 5000 revolutions per minute around a cylindrical shaft; liquids enter and leave through the shaft; they flow radially and concurrently in the rotating drum.

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