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XXVI. A new Form of Magnetic Torsion-balance and Magna* 

 tometer. By Frederick John Smith*. 



IX the torsion-balance, such as used by Coulomb to measure 

 magnetic forces, t^vo poles of the suspended magnet are 

 acted on? The end the author has had in view is so to place 

 one pole of the suspended magnet thatit shall not be acted on 

 by horizontal pull. A magnet of rectangular shape, X B S, 



Tig. 1. 



= N 



fig. 1, having a brass counter- 

 weight A B. is suspended by the 

 filaments C D so that the south 

 pole is in the axis of rotation of 

 the whole mass: thus the magnet 

 may be regarded as having only 

 one pole that can be acted on by 

 horizontal force. In addition to , — 

 this, a little mirror is so placed A 

 on an axis, M, and attached to 

 S by a short lever P, that the 

 ratio of the deflection of X to the 

 rise of the whole mass is at once 

 shown on the scale, E, by the 

 usual reflecting method. In the 

 magnetometer for determining 

 the pole-strength of magnets the 

 same kind of rectangular magnet is used, attached to a single 

 horizontal wire, A B, fig. 2 ; the magnet is furnished with a 

 mirror-scale and lamp. 



Fig. 2. 



y 



Is P S, rectangular magnet ; S, mirror ; R, scale and lamp. 

 The instrument is used thus: — The weight at Q and the mag- 

 net X' S / being removed, the magnet X P S is set in a hori- 

 zontal position by means of the torsion-wire ; then a known 

 weight, Q, is placed at M, M P = P X, and the deflection on 

 the scale is recorded ; then the weight is removed, and the 

 * Communicated bv the Author. 

 Q2 



