94 



Puller's Calculating Slide-Scale. See Slide-Rule. [2, 13, 15, 20. 



21, 24, 25, 26, 27.] 



Galactometer. An instrument for ascertaining the quality of 

 milk by its specific gravity ; a lactometer (q.v.). [5, 13.] 



Galact's Densimeter. A galactometer (q.v.). 



Galilean Binocular. See Binocular. [15.] 



Galilean Telescope. See Telescope. 



Gallows Square. A drawing or setting out square for ship 

 architecture. [15, 21.] 



Galton's Whistle. An acoustical instrument for testing the 

 limits of human audibility. It consists of a fine bore brass 

 tube with adjustable screw piston, and air bellows. 



Galvanic Battery. A number of connected galvanic cells. (See 

 Battery.) 



Galvanometer. An instrument for measuring electric currents, 

 usually by the deflection of a magnetic needle in the magnetic 

 field created by an electric current, or by the deflection of 

 a moving coil, carrying the current, in the field of a fixed 

 magnet. There are thus two main types, the moving magnet 

 and the moving coil galvanometer. [4, 10, 13, 19, 16.] 



Galvanometer, Astatic. A moving magnet galvanometer in 

 which the sensibility is increased by employing an astatic 

 needle, i.e., a combination of two magnetised needles with 

 their poles turned opposite ways. [4, 16, 19.] 



Galvanometer, Ballistic. A moving magnet galvanometer in 

 which the needle and its attachments have a large moment 

 of inertia. Used to measure the total quantity of electricity 

 that passes in currents of short duration. [4, 16, 19.] 



Galvanometer, Broca. A moving magnet galvanometer in which 

 the magnet system consists of two steel wires placed vertic- 

 ally and each so magnetised that its two ends are of like 

 polarity, with a consequent pole in the middle. [4, 19] 



Galvanometer, D'Arsonval. A moving coil galvanometer. The 

 magnetic field is produced by a number of horse-shoe 

 magnets laid one above the other, their feet being so shaped 

 as to leave a vertical cylindrical hollow. 



Galvanometer, Differential. A galvanometer with two equal 

 coils nearly coinciding with one another, each connected to 

 its own pair of binding screws. Used to measure the 

 difference of two currents. 



Galvanometer, Double Coil. An astatic galvanometer invented 

 by Lord Kelvin. [4, 16.] 



Galvanometer, Einthoven String. A very sensitive moving coil 

 galvanometer in which the coil is reduced to a single very 

 fine fibre or " string " passing between the poles of a 

 powerful electromagnet. [4.] 



Galvanometer Lamp and Scale. The lamp and scale used with 

 the mirror or other galvanometer (q.v.) in which the 



