84 ELEMENTS OF LABORATORY WORK 



57. Deflection of a Freely Suspended Magnet by a Sub- 

 stance forming part of an Electric Circuit, When a lightly 

 suspended magnet is brought near to a conducting body which 

 is in connection with the copper and zinc of a cell, or which in 

 any way forms part of an electric circuit, stress between them 

 may be observed. The magnet always tends to take up the 

 same position, for if displaced from this position it returns 

 after some oscillation. 



The magnet tends to place itself at right angles to that 

 axis of the conductor which lies between the points of connec- 

 tion with the rest of the system. The relative distances from 

 those points, or the plane in which the magnet is held, does 

 not alter this tendency ; but on increasing the distance from 

 the conductor itself the stress rapidly decreases. 



It is convenient to take a wire as the connecting con- 

 ductor. The magnet will always tend to set itself at right 

 angles to the wire. Since the stress between the wire and 

 the magnet is the same in all positions, provided the vertical 

 distance from the conductor be unaltered, the ends of the 

 magnet are reversed when it is moved half-way round the 

 wire, i.e. from above to below the wire, or from one side to 

 the other. 



If, then, the wire is turned upon itself, so as to form a loop, 

 the stress is intensified ; and still more so if the wire is 

 wound into a coil containing many loops. A magnet suspended 

 at the centre of a coil will indicate by its movement when the 

 coil forms part of an electric circuit. Such an arrangement is 

 seen in a galvanometer. 



All magnets, when freely suspended, are always so turned 

 that their position with regard to the earth is the same. 

 There is a distinct stress between them and the earth. Con- 

 sequently, the displacement produced on a magnet by a con- 

 ductor in a circuit must depend on the relative magnitude of 

 the two stresses ; and consequently, the magnet will sometimes 

 only tend to set itself at right angles to the coil. 



From this fact we learn also that the position of the con* 

 ductor or coil in a galvanometer must not itself be at right 

 angles to the position which a magnet assumes on account of 



