. Maximum output with some simple thoughts...
Magnets and Currents
In the twelfth century, there was introduced into Europe from China a simple instrument which changed journeying on the sea from uncertain wandering to a definite, safe voyage. This instrument was the compass, and because of the property of the compass needle (a magnet) to point unerringly north and south, sailors were able to determine directions on the sea and to steer for the desired point.
Since an electric current is practically equivalent to a magnet, it becomes necessary to know the most important facts relative to magnets, facts simple in themselves but of far-reaching value and consequences in electricity. Without a knowledge of the magnetic characteristics of currents, the construction of the motor would have been impossible, and trolley cars, electric fans, motor boats, and other equally well-known electrical contrivances would be unknown.
FIG. - The compass.