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.
From white-wood, half an inch thick, cut two blocks three inches and a quarter square. In one of them (the rear one) bore a hole at the centre, of such size that a piece of three-eighth-inch gas-pipe can be screwed into it. In the other one make a hole two inches in diameter, so that the cover of a small tin can will fit into it. Outside this hole, and on one side of the block, cut the wood away and down for one-eighth of an inch, forming a rabbet, as shown at A in [Fig. 7]. This will be the back of the front block.
