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Compasses, Triangular. Drawing compasses or dividers with 

 three legs, enabling three known positions to be accurately 

 and quickly marked off. [2, 5, 13, 15, 16, 17, 20, 21, 24, 

 26, 27, 28.] 



Compasses, Vertical Drawing. [15, 21.] 



Compensating Eyepiece. See Eyepiece. [1, 2, 3, 20, 22, 26.] 



Compensator. A piece of soft iron or magnet to neutralise the 

 effect of the iron of a ship upon the compass needle. [15, 

 16, 28.] 



Compression Extensometer. See Extensometer. [4.] 



Compressor. A microscope fitting for holding live objects with 

 a gentle pressure. [2, 3, 20, 26.] 



Compound Pendulum. See Pendulum. 



Computer. A transparent sheet ruled with squares for com- 

 puting areas on plans drawn to scale. [13, 15, 21, 24, 27.] 



Computing Scale. A rule with sliding index frame for com- 

 puting areas on maps. [15, 21, 24, 25, 27.] 



Concave Lens. See Lens. [1, 2, 3, 8, 9, 10, 11, 13, 15, 17, 20, 26.] 



Concave Mirror. See Mirror. [1, 2, 3, 8, 10, 11, 13. 15, 17, 20, 26.] 



Concave Plane. A compass plane for smoothing curved surfaces. 



Concentric Eyepiece. See Eyepiece. [2. 3, 10, 22, 27.] 



Conchometer. An instrument for measuring biological shells, 

 and the angle of their spire. 



Condenser. (i) An optical system of lenses for converging light 

 to a point. (2) Two electrical conductors, usually of thin 

 plates or sheets of metal, with a larger plate of non-con- 

 ducting material between them, e.g., a. Leyden jar. [1, 2, 

 3, 8, 9, 10, 11, 14, 17, 20, 22, 26.] 



Condenser, Abbe. A non-achromatic and non-aplanatic system 

 of lenses used to concentrate a wide-angled cone of light 

 upon an object viewed by the miscroscope. [2, 3, 9, 17, 



20, 22, 26.] 



Condenser, Achromatic. A system of lenses corrected for 

 chromatic aberration used for illuminating, with a wide 

 angle, transparent objects when viewed with the micro- 

 scope. [2, 3, 11, 20, 22, 26.] 



Condenser, Apochromatic. An optical condenser in which the 

 lenses are corrected for the secondary spectrum. [2, 3, 20, 

 22, 26.] 



Condenser, Bull's Eye. A convex lens used for converging or 

 rendering parallel a beam of light. [2, 3, 8, 9, 10, 17, 20, 



21, 22, 26.] 



Condenser, Cardioid. A dark ground illumination employing 

 cardioid reflectors. [2, 22, 26] 



Condenser, Paraboloid. A reflecting glass paraboloid for micro- 

 scopic dark ground illumination in the observation of living 

 bacteria. [2, 3, 20, 22.] 



Condenser Thermometer. See Thermometer. [5, 6, 13, 15, 17, 

 20, 21.] 



