Fig. 225.
Fig. 224 shows, by diagram, a coil H, suspended so that it can move easily, its ends being joined to a current reverser, and this, in turn, to a dry cell D C. A magnet, H M, will attract the core of H when no current passes. When the current is allowed to pass first in one direction and then in the opposite direction, by using the reverser, the core of H will jump back and forth from one pole of H M to the other. There are many ways by which motion can be produced by the current, but to have it practical, the motion must be a rotary one. (See "Study," Chapter XXVI., for numerous experiments.)
Fig. 226.
161. The Electric Motor is a machine for transforming electric energy into mechanical power. The construction of motors is very similar to that of dynamos. They have field-magnets, armature coils, commutator, etc.; in fact, the armature of an ordinary direct current dynamo will revolve if a current be passed through it, entering by one brush and leaving by the other. There are many little differences of construction, for mechanical and electrical reasons, but we may say that the general construction of dynamos and motors is the same.
Fig. 225 shows a coil of wire, the ends of which are connected to copper and zinc plates. These plates are floated in dilute sulphuric acid, and form a simple cell which sends a current through the wire, as shown by the arrows.
Fig. 227.