73 



Communicator, Electrical. An electrical type of communicator. 



Communicator, Mechanical. A mechanical type of commu- 

 nicator. 



Commutator. An instrument which periodically interrupts an 

 electric current. Also a key enabling the direction of an 

 electric current in a circuit to be readily reversed. [16, 19.] 



Comparator. An instrument for accurately measuring lengths 

 or checking scales by comparison with a standard scale. 

 [3, 4, 21.1 



Comparator, Co-ordinate. An apparatus for the analysis of 

 physiological and other records, by measurements made 

 with a micrometer microscope. Particularly suitable for 

 measuring photographic records on either plates or paper. [4.] 



Compass. An instrument for indicating directions upon the 

 earth's surface by means of a magnetic bar or needle turning 

 freely upon a pivot, and pointing in a northerly and 

 southerly direction. The needle may move over a fixed 

 dial or have the dial attached to, and moving with, it. 

 [2, 5, 6, 9, 13, 15, 16, 17, 18, 20, 21, 24, 25, 27, 28.] 



Compass, Aviation. A form of compass designed for use on 

 aeroplanes. [9, 13, 15, 16, 17, 20, 21, 27.] 



Compass, Azimuth. A compass with a card divided into degrees 

 and having vertical sights. [13, 15, 16, 17, 20, 21, 25, 27, 

 28.] 



Compass, Burnet Bearing Clamping. A liquid azimuth compass, 

 for use in boats and small yachts, having a device for 

 clamping the card the moment the bearing is observed. 

 [15, 28.] 



Compass, Charm. A small, magnetic compass, mounted in 

 various designs, in gold or silver, for attachment to the 

 watch chain. [2, 3, 5, 9, 13, 15, 16, 17, 20, 21, 27.] 



Compass, Creagh-Osborne. A liquid compass designed for 

 military, naval and aeronautical uses. [13, 15, 16, 20, 26, 

 27.] 



Compass, Jumper Stay. A compass suspended from the jumper 

 stay of a ship, with an arrangement for locking the card 

 and then lowering it to the deck. The compass being sus- 

 pended at a height above the vessel's deck, is not affected 

 by the magnetism of the ship. [13, 28] 



Compass, Kelvin. A short needle, light card form of compass. 



Compass, Lifeboat Pattern. A boat compass for use on life- 

 boats, usually to B.O.T. specification. [13, 15, 16, 28.] 



Compass, Liquid. A compass having the card floating in liquid 

 so as to damp the oscillations. [13, 15, 16, 28.] 



Compass, Marching. A pocket magnetic compass having a 

 movable indicator which can be set to the angle between 

 the North and South magnetic meridian and the marching 

 direction. [2, 5, 6, 10, 13, 15, 16, 17, 20, 21, 24, 25, 26, 27.] 



Compass, Overhead Pattern. A ship's compass arranged for 

 observation from below the card. [13, 15, 16, 28.] 



