“Since sound radiates in all directions, it follows that, if such radiation be prevented by confining it in tubes, it may be carried to a great distance with very little diminution of its effect; and hence the use and application of those trumpets, or tin speaking-pipes, which are now commonly used for conveying intelligence from one part of a house to another. The trumpet used by deaf persons acts on the same principle; but as the voice enters the trumpet at the large instead of the small end of the instrument, it is not so much confined, nor is the sound so much increased.”
“I believe,” said Mrs. Seymour; “that the experiment exhibited some time since in London under the title of the Invisible Girl, and which excited such general curiosity, was discovered to depend upon an arrangement of this kind.”
“I expected that you would allude to that exhibition,” said Mr. Seymour; “and as I was anxious to provide my young pupils with some new amusement, as a reward for their industry, I have directed Tom Plank to construct the necessary apparatus for exhibiting and explaining the deception. On our return to the lodge, I have no doubt we shall find that every arrangement for the performance has been completed.”
Miss Villers was now gratified by a view of the more interesting specimens in the geological temple. Mr. Seymour also explained the design of the pillars which had so greatly excited her curiosity.
On the return of the party, Mr. Seymour found, as he had anticipated, that the necessary apparatus for the experiment of the “Invisible Girl!” had been duly arranged, and that Tom Plank was in attendance to afford any assistance which might be farther required. We shall proceed to describe all the visible mechanism, as it appeared to the children on entering Mr. Seymour’s study, and of which we here present the reader with a perspective sketch.
It consisted of a wooden frame, not very unlike a bedstead, having four upright posts, a a a a, and a cross-rail at top and bottom to strengthen them. The frame thus constructed stood upon a low table, and from the top of each of the four pillars sprang four bent brass wires, which converged to the point c. From these wires a hollow copper ball was suspended by ribands, so as to cut off all possible communication with the frame. The globe was supposed to contain the invisible being, as the voice apparently proceeded from the interior of it; and for this purpose it was equipped with the mouths of four trumpets, placed around it in a horizontal direction, and at right angles to each other, as shown in the annexed section, in which the globe is represented in the centre; d d d d are the trumpets, and b b b b the frame surrounding them, at the distance of about half an inch from their mouths. Such as we have described was the apparatus, which had been constructed under the direction of Mr. Seymour, who informed the party that, if any of them would ask a question of his little fairy, and direct the voice into one of the trumpets, an answer would immediately be returned from the ball.
“Let me interrogate her,” exclaimed Louisa, as she advanced towards the railing. “Tell me, mysterious being, the name of the person who now addresses you.”
“Miss Louisa Seymour,” answered a voice sufficiently audible to Louisa, whose ear was near the mouth of the trumpet, and yet so distant and feeble, that it appeared as if coming from a very diminutive being, and thus heightened the deception. Each of the party successively asked some question; and the surprise of the children may be more easily imagined than described. Tom examined the ball, the trumpets, and the framework; but he was unable to discover any clue by which he could unravel the mystery. At length Mr. Seymour proceeded to the explanation. He told them that the mechanism owed its effects to the combined operation of two principles with which they were already acquainted; the concentration and conveyance of sound by means of a speaking-pipe, and its reflection from an appropriate surface so as to change its apparent direction, by producing an artificial echo. He then showed them the pipe which was concealed in one of the legs of the frame, and explained in what manner the voice of Tom Plank, who had been stationed in an adjoining room, was conveyed to the mouth of the trumpet, and thence reflected to the ear of the observer. By means of the annexed section, we shall hope to render this subject as intelligible to our readers, as did Mr. Seymour to his little pupils.