If both spools were wound in the same direction they would be in opposite directions when the U were straightened out, and would cause like poles at the same ends. These poles would neutralize one another, so that there would be no magnetic attraction.
This can be readily proved by joining together the two yoke ends and the two armature ends of the spool wires. Then pass the current through these two joined connections.
Fig. 16 Fig. 17 Fig. 18 Fig. 19
The Push Button.
Push buttons, or pushes, are made in a variety of forms, with metal, wood, hard rubber, or porcelain bases.
[Fig. 16] has a metal base, and is suitable for a front door.
[Fig. 17] is a wooden pear push, and is attached at the end of a cord which has the two conductors braided in it, each, however, having its own insulation.
[Fig. 18] is a plate push for an outside door.
[Fig. 19] is either of metal, wood, or porcelain, and is the shape most commonly used.