CHAPTER IX

ACOUSTIC PRINCIPLES

IN THE field of acoustics, the principles available for magical purposes are but few. But those are extremely valuable, principally in combination with methods of other types. There are, it is true, one or two well-known inventions in which this branch of physics has been made the basis for illusionary devices; but, as a rule, it is applied to magic only as an adjunct, and by way of subsidiary effect.

The first principle of this type is that of Mock Sound. It comprises all devices for the simulation of characteristic noises, such as normally occur in certain circumstances but would be lacking when things are not precisely what they seem. In magic it often happens that, since the things done and the things used are not exactly what they appear to be, sounds that would naturally accompany certain operations do not necessarily occur at the appropriate moments. Thus, if what appears to be a heavy weight is in reality nothing more than an inflated envelope, no sound will accompany the action of putting it down upon a carpeted stage. Therefore, in order to complete the illusion, it is desirable that, at the proper instant, the sound of a weight coming in contact with the floor be imitated.

In this case, of course, the best imitation is the real thing, a weight being dropped off-stage, as near as may be to the imitation article. The chief point would be to make sure that sound and action coincide. Otherwise, the "artistic verisimilitude" must become not a trifle worse than useless. In some cases, the sound accompanying a secret operation resembles that incidental to the operation apparently performed, thus avoiding all need for other simulation. An instance of this is the chinking of coins when conveyed into the palm of one's hand, while they appear to be thrown from one hand to the other. The devices for imitating characteristic sounds are many and of various kinds. Some are mechanical, like the "ticker" which gives the sound of a watch. Others are manual, like the simple devices used for imitating the rattling of covered objects which are not under the cover. Such methods, in common with the generality of this type, are well understood and require no particular reference in this place.

Conveyance of Sound is a principle which, at first sight, would seem to be capable of wide development in connection with magic.

The fact is, however, that the practical difficulties to be overcome in rendering the mode of conveyance secret or (at the least) not easy of detection, are very great. The conveyance of messages by speaking-tube a method formerly used in certain forms of so-called "second-sight," can scarcely be regarded as an adaptation of the present principle. This particular group of acoustic devices, properly speaking, includes only those intended for the conveyance of sounds audible to the audience. The illusion known as "The Invisible Orchestra" is an example of tricks upon this principle. In that invention, the sound was conveyed by wooden rods from instruments below the stage to their counterparts above. Another trick belonging to this group is that which was used in connection with "The Speaking Head" illusion. In that instance, the sound was carried by tube to a wide-mouthed orifice, and received in another attached to the head itself and thence to the mouth, from which the sounds were supposed to emanate. The device, however, was not very satisfactory in its operation. As may be anticipated, sounds so conveyed would obviously have their origin elsewhere than in the head itself. These two examples will suffice to indicate the nature of the drawbacks inherent to this principle, from a magical standpoint.

The Disguise of Sound is a principle seldom employed in magic, except in so far as it relates to drowning one sound by another. The converse application is that of preventing the occurrence of sounds, which would otherwise disclose operations intended to be kept secret. The latter object, however, is usually attained by physical means, rather than by the aid of acoustic principles. Thus the disguise of sound would 'ordinarily consist in the prevention of sounds not wanted and the substitution of sounds required.

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