2 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



stretched near one end of a magnet, as shown in Fig. I , the wire 

 is pushed sidewise as indicated in the figure. When an electric 



battery 



Fig. 2. 



current flows through an insulated wire which is wound around 

 an iron rod, as shown in Fig. 2, the iron rod is magnetized, as 

 indicated by the letters JVS. These effects constitute particular 



cases of what may be called in 

 N general the magnetic effect of the 

 electric current.* The magnetic 

 effect of the electric current, which 

 is shown in its simplest aspect in 

 Fig. i, is exemplified in a common 

 form of ammeter, the working parts 



of which are shown in Figs. 30 and 3^. A horse-shoe magnet 

 of steel is provided with soft iron pole-pieces NN and SS, be- 

 tween which a soft iron cylinder C is rigidly supported by being 

 bolted to the brass strip A. In the spaces between the pole- 

 pieces and the cylinder C move the sides or limbs of a small 

 coil of wire which is delicately supported upon a pivot and which 

 carries a pointer which plays over a divided scale. Current is 

 led into this movable coil through the hair-spring at one end and 

 through a very flexible conductor at the other end, and the side 

 force which is exerted upon the limbs of the coil by the magnet 



* Another aspect of the magnetic effect of the electric current, namely, the pro- 

 duction of current in a wire when the wire is in motion near a magnet, is discussed in 

 Art. 63. 



