Chapter XV · THE MAGIC DRUM.

At the command of the magician, a drum, placed upon a slender tripod-stand, beats sundry marches with the skill and precision of a regimental drum-major; with this difference, however, that the magic drum sounds without the aid of drum-sticks, and without any visible controlling power.

This performance takes place in the first instance upon the stage, but in order to preclude all suspicion of an acoustical illusion, the performer afterwards hooks the drum on to a couple of cords hanging from the ceiling of the hall. The instrument, swinging backwards and forwards over the heads of the spectators, seems to acquire fresh vigour and spirit in the execution of its marches and roulades.

This marvellous performance, which might readily be made to pass for a spiritualistic manifestation, rests on an extremely simple principle. Within the drum is a vibrateur de la Rive, more commonly known as an “electric bell” movement. (The reader will find a full description of this kind of bell in any work on electro-dynamics, and particularly in the treatises of Count du Moncel.) The hammer of this movement is so arranged as to strike on the skin of the drum by way of “bell.”

It is well known that, as part of the mechanism of an electric bell, there is always, at a greater or less distance from the bell itself, a stud or “push,” which has only to be pressed in order to set the apparatus in motion. So long as the finger rests upon this stud, the metallic vibrations continue to be heard; only ceasing when the pressure is removed.

This stud is placed behind the scenes, ready to the hand of an assistant, who plays the part of the invisible medium. Artfully concealed wires and metallic connections communicate with the inside of the drum, whether placed on the tripod, or hanging by the cords.

With these appliances the execution of any military music is an extremely simple matter, since you have at your disposition raps and rolls of any given duration.

In point of fact (and the experiment may be tried upon the push of an electric bell) if you press the stud for an extremely short time, the value of a semi-quaver for instance, the hammer will only strike a single tap. This is the “rap,” or single stroke of the drumstick. As to the various rrrrr or “rolls,” they are produced by durations of pressure equivalent to quavers, crochets, minims, &c. The drum becomes simply an instrument on which the assistant plays, with greater or less execution.

To give greater spirit to the performance of the drum, a second vibrator may be added within, and a second push under the hand of the assistant, who can then with one hand keep up a continuous roll, while with the other he beats the measure of the march. This, in drum practice, is a special feat, to be executed only by the most skilful performers.

In order to make the execution more perfect, a “barrel” may be constructed as in organs, the pins upon which, duly placed, will transmit the electric fluid at the exact intervals necessary for the due execution of the roulades desired.

THE END.

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