97 



Gauge, Draught. For measurement of pressure slightly above or 

 below that of the atmosphere, as chimney draughts, etc. 

 Usually consists of a U-tube containing water, mercury or 

 other liquid, provided with a suitable scale. [15.] 



Gauge, Dry. A gas -pressure gauge which contains no liquid. 



Gauge, Edney's Air-Pressure. A self-recording air or draught 

 gauge. 



Gauge, Footner's Railway. A gauge used by railway engineers 

 foi indicating the banking of the outer rail on a curve. [15, 

 21, 27.] 



Gauge, Gas. For testing the pressure in gas supply pipes. [4, 

 5, 6, 13, 17, 21, 26.] 



Gauge, Hole. A taper tool or instrument with graduated scale 

 for determining the size of holes. See also Petrnl-.Ta.nk 

 Gauge, Pit-Water Gauge, Steam-Gauge. 



Gauge, Hydraulic. For high pressure such as those produced by 

 hydraulic pumps. [5, 17. ] 



Gauge, Vacuum. An instrument for indicating the difference 

 between the external atmospheric pressure and the pressure 

 inside a partially exhausted vessel. May be constructed on 

 the Bourdon principle (see above) or may depend on the use 

 of aneroid boxes, diaphragms, etc. [-5, 13, 15, 16, 17, 21, 28.} 



Gauge-Glass Protectors. An attachment for the prevention of 

 injury to the attendant in case of breakage of the gauge- 

 glass. [15.] 



Gay-Lussac Alcoholometer. See Alcoholometer. 



Gay-Lussac Barometer. See Barometer. 



Gay-Lussac Densimeter. See Densimeter. 



Geissler's Tube. A glass tube provided with platinum electrodes 

 and containing some gas under very low tension, which 

 becomes luminous when an electric discharge is passed 

 through it. [26.] 



Geocyclic Machine. A machine for demonstrating the simple 

 processes by which day and night, and the seasons, are 

 produced. 



Geodescope. A combined celestial and terrestrial globe. 



Geometric Pen. An instrument for drawing geometric curves, 

 in which the movements of a pen or pencil, attached to a 

 revolving arm of adjustable length, may be indefinitely 

 varied by changing the toothed wheels which give motion 

 to the arm. [13, 17, 21, 25, 26.] 



Geometric Square. A portable instrument in the form of a 

 square frame for ascertaining distances and heights by 

 measuring angles. [13, 21.] 



George's Artificial Horizon. See Artificial Horizon. [6, 13, 15, 

 17, 21, 24, 27.] 



Geoscope. See Orrery. 



Geothermometer. An instrument for measuring the temperature 

 of the earth at different depths, as in mines and wells. [21.] 



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