There are various forms of the magneto-electric machines, as well as of commutators, but the foregoing shows the general principle of them all.
Fig. 4.
Dynamo-electric Machines.
It will now be necessary to explain the nature of a dynamo-electric machine, called, for shortness, a dynamo, and to show in what it differs from a magneto-electric machine.
I have explained how an electric current is produced by a wire passing in front of a magnet; now, this magnet may either be of the ordinary kind, or it may be what is termed an electro-magnet. Current will magnetise an iron or steel bar. One of the effects which electricity can be made to produce is the magnetising of steel bars to form the ordinary and well-known permanent magnets which are used in ships’ compasses, &c. To produce this effect, part of the wire in a circuit is made into a spiral as in [Fig. 5].
Fig. 5.