Fig. 41.
According to Mr. Jensen's system of electric bells, the bell may take any desired form, that of the ordinary church bell being preferred, and the electro-magnetic apparatus is placed entirely inside the bell itself. To attain this end the electro-magnetic apparatus must be compact in form. A single electro-magnet has pole pieces at each end opposite to which an armature is suspended from a pivot and balanced by the hammer of the bell. At the back of the armature there may be a make and break arrangement, whereby a continuous succession of strokes is effected, or this may be omitted,
in which case a single stroke is given when the contact with the battery is made, or both may be effected by separate wires, make contact with one wire, and a single stroke is struck; make it with the other and the current passes through the make and break and a succession of strokes is heard. When the contact-breaker is used, it is so arranged that a slight rub is caused at every stroke, so keeping the contact clean. The flexible break, with the ingenious wiping contact, is a great improvement over the ordinary screw, which often becomes disarranged.
The form of the magnet is such that a considerable
degree of magnetic force is caused by a comparatively small battery power. The electro-magnetic apparatus being within the bell the latter forms a very effective and handsome shield for the former. Not only can the bell shield the electro-magnet from wet but the whole of the conducting wires as well.
The bell may be screwed to a tube through which passes the conducting wire, which makes contact with an insulated metallic piece in the centre of the top of the bell. Both the wire and the contact piece are as completely shielded from the weather as if within the bell itself.
