62 



Battery, Electric. A group of electrical elements (e.g. L yden 

 jars or chemical cells) arranged in series or in parallel, so as 

 to yield an electric current. [17, 26.] 



Battery, Gravity. A battery in which the different liquids range 

 themselves at different heights by virtue of their different' 

 specific gravities. 



Battery Hydrometer. See Hydrometer. [5, 6, 13, 15, 17, 21.] 



Beale Neutral Tint Reflector. See Reflector. [2, 3, 1 7, 20, 22, 26.] 



Beale's Deviascope. See Deviascope. [J5.] 



Beam Compass. An instrument consisting of a wooden or brass 

 beam having sliding sockets carrying steel or pencil points. 

 Used for describing large circles the radii of which are 

 beyond the extent of the common compasses, and also for 

 transferring lengths to be measured. [2, 5, 6, 13, 15, 16, 17, 

 19, 20. 21, 24, 25, 26, 27.] 



Beam Compass. A simple form of triangular compasses for 

 copying large plans. [2, 13, 15, 17, 20, 21, 26, 27.] 



Beam Compass, La Trobe. A light form of beam compass, con- 

 sisting of two runners attached by a flexible strap which, if 

 compressed slightly, instantly releases them. [13, 21.] 



Beam Compass, Roller. A beam compass with roller adjustment. 

 [2, 6, 13, 16, 20, 21, 24, 26, 27.] 



Beck-Thorp Pocket Diffraction Spectroscope. See Spectroscope. 



Begnin Slide-Rule. See Slide-Rule. [15.] 



Bell's Naval Station Keeper. See Naval Station Keeper. [13, 15, 

 17, 20.] 



Bench, Lens-Testing. An apparatus for measuring the aberra- 

 tions of lenses. [2, 3, 10, 17, 21, 26, 27.] 



Bench, Optical. An apparatus for making optical experiments 

 and tests. [2, 3, 4, 10, 17, 19, 21, 26, 27.] 



Bench, Photometric. A bench which carries the apparatus for 

 measuring the intensity of a source of light by comparison 

 with a standard. [3, 10, 27.] 



Benson's Comb Nephoscope. See Nephoscope, Benson's Comb. 

 115, 17.] 



Besidometer. An instrument which indicates the proper distance 

 of spectacles between the hinges ; that is, the breadth of the 

 forehead. 



Bevel Protractor. A form of flat bevelled protractor for setting 

 off angles. [5, 6, 15, 16, 17, 20, 21, 24, 25, 27.] 



Bifilar Micrometer. See Micrometer. [2, 3, 11, 17, 20, '22, 25, 26. 



Bilge-Water Gauge. A gauge for showing the depth of bilge- 

 water in the hold of a ship. [13, 15.] 



Bi-Meter CO Recorder. See CO Recorder. [4.] 



Binnacle. The case box or stand by which the compass on 

 board ship is protected. [13, 15, 16, 17, 28.] 



Binocular. An instrument (e.g., Microscope, Telescope or 

 Magnifier) having two tubes, each furnished with lenses, for 

 the use of both eyes at once. The term is also used as a 



