Page:Incandescent electric lighting- A practical description of the Edison system.djvu/27

 greatest possible number of these lines in a given time.

And here it becomes necessary to lay aside the permanent horseshoe-magnet, which has served us so well up to this point in our explanation, and substitute in its place the practical electro-magnet.

If we retain the shape of the horseshoe (see fig. 6), and make our magnet of soft iron—instead of steel, the material of which the permanent horseshoe-magnets are made—we shall have a device which will need something to charge it with magnetism whenever it is brought into use; this something is the electric current^ and we supply it to the magnet by winding one or more coils of insulated wire about the legs of the magnet near their ends.

It is necessary that there should be a slight trace of magnetism in these electromagnets, in order that the electric current may have something to act upon to assist it in creating the necessary magnetic condition in the generator; this want is