H7 



Magnetic Balance. A simple instrument for experiments on 

 magnets. [16, 19.] 



Magnetic Battery. A combination of bar or horse-shoe magnets 

 with the like poles adjacent, so as to act together with great 

 power. [16, 26.] 



Magnetic Compass. See Compass. [5, 13, 15, 16, 20, 24, 25, 27.] 



Magnetic Compensator. A contrivance connected with a ship's 

 compass for compensating or neutralising the effect of the 

 iron of the ship upon the needle. [15, 16, 28.] 



Magnetic Needle. A light bar of steel magnetised, and sus- 

 pended at its centre on a sharp pointed pivot or by a 

 delicate fibre so that it may take up freely the direction of 

 the magnetic meridian. It constitutes the essential part of 

 the magnetic compass. [13, 15, 16, 17, 21, 24, 27.] 



Magnetic Standard (Duddell's Magnetic Standard). An instru- 

 ment consisting essentially of a pair of fixed coils, through 

 which an electric current is passed ; and a pair of moving 

 coils, which can be rotated in the magnetic field produced 

 by the fixed coils, thus producing an induced electric current. 

 Its principal purpose is the calibration of ballistic galvano- 

 meters under conditions identical with those under which 

 they will be used. [4.] 



Magnetic Standard iHibbert's). 



Magnetic Telegraph. A telegraph acting by means of a magnet. 



Magneto-Electric Machine. A form of dynamo electric machine 

 in which the magnetic field is maintained by permanent steel 

 magnets. [17.] 



Magnetograph. An instrument for registering, by photography 

 or otherwise, records of the states and variations of any 

 terrestrial magnetic elements. [4, 6, 15, 17, 21] 



Magnetometer. An instrument for the measurement of magnetic 

 declination and of the horizontal component of the earth's 

 magnetic force. It consists essentially of a magnetic needle 

 or bar, suspended so as to swing freely in a horizontal 

 plane. According to the suspension the magnetometer may 

 be Unifitar or Bifilar, and according to the observations 

 required may be Vibration or Deflecting. [4, 13, 15, 17.] 



Magnetometer. A voltaic series of two or more large plates 

 which produce a great quantity of electricity of low 

 intensity, adapted to the exhibition of electromagnetic 

 phenomena. [13, 17.] 



Magnifier, Aplanatic. A magnifying lens corrected for spherical 

 aberration. [1, 2, 3, 9, 10, 15, 17, 20, 21, 22, 25, 26, 27.] 



Magnifier, Binocular. A combination of two magnifying glasses 

 for stereoscopic observation of small solid objects. [2, 3, 

 10, 13, 15, 20, 26, 27.] 



Magnifier, Chart. A hand magnifying lens for reading the 

 soundings and other marks on a chart. [2, 13, 15, 16, 20, 

 21, 27, 28.] 



