The wiring is at the under side of the base and is shown in Fig. 6. The current enters binding-post A, and passes around coil and magnet No. 1 by entering at B and leaving at C; from thence to D, entering the armature spring at E, when the small spring has drawn the knocker-bar over to the left. The current passes along the armature and out at F; then along to binding-post G, and so on around through battery K and push-button L, thus completing the circuit. Directly that this is done the magnet draws the spring end of the armature away from contact-point D and up against contact-point J, so that the circuit is broken through coil No. 1 and is sent through coil No. 2. This immediately magnetizes core No. 2 and draws the armature down to it, breaking its contact with J and re-establishing it with D. The rapid alternate making and breaking of the circuit, and the rapid and strong motion of the armature in its seesaw action, causes the knocker to rap the bells soundly each time it travels from right to left and back again. Two bells of similar size, or two drums or wooden boxes, may be employed for this double striker, and the more current that is run through the coils the more power and a corresponding increase of noise. An Electric Horn One of the most useful pieces of apparatus where a loud noise is required (such as in a motor-boat or an automobile) is the electric horn. It is a rearranged principle of the telephone, for instead of sound entering or striking against the membrane or tympanum to be transmitted elsewhere, the disturbance takes place within the horn and the sound is emitted. Everybody has been close to a telephone when others have been using it, and has heard noises, rasping sounds, and even the voice of the speaker at the other end of the line. If a cornet were played at the other end of the line it could be distinctly heard through the receiver by many persons in the room, since its vibrations are loud enough to set up a forcible succession of sound-waves. The same principle operates in the electric horn, but instead of being agitated at a long distance it is done within the enclosure, and a very much louder vibration is consequently produced. It is quite as easy to make an electric horn as to construct a bell, but care must be exercised to have the parts fit accurately and the wiring properly done. If the drawings are studied and the description closely followed, there is no reason why a horn cannot be made that will demand any one’s attention from some distance away. The complete horn is shown in the illustration Fig. 7, and as it is made of wood it is easily attached with screws to a boat or a motor-car.