The first part of the toy to construct is
The Electro-magnet. The difference between an electro-magnet and the toy variety of horse-shoe magnet with which every boy is familiar, is that the electro-magnet retains its magnetism only so long as an electric current is passing around it, while the steel magnet retains its influence permanently, after being magnetized, unless it happens to be demagnetized by subjection to heat, or in some other way.
Fig. 176.—An Electro-magnet Derrick.
[Figures 177] to [179] show the details for making a simple home-made electro-magnet.
An electro-magnet consists of a center core of soft iron, wrapped with a coil of insulated wire. When an electric current passes over a wire, a magnetic field is formed around the wire; and when several turns of insulated wire are wrapped about a soft iron core, the magnetic fields of all the turns of the coil, or helix, combine, forming a very strong magnetic field which strongly magnetizes the iron core. As I have said before, this magnet loses its magnetic influence the instant the current ceases to pass through the surrounding coil of wire.