This curious phenomenon is precisely analogous to the production of the mirage, or phenomena of un equal refraction, which are occasioned by the mix ture of portions of air of different refractive density.
5. Explanation of the deception of the invisible Girl.
In our article ACOUSTICS, we have mentioned in a few words the principle of this very singular decep tion, which was some years ago exhibited in London and Edinburgh by M. Charles.
A perspective view of the apparatus by which this deception was performed, is shown in Plate CCCCLXXXIV. Fig. 1, a plan of it in Fig. 2, and a section of it in Fig. 3.
The apparatus shown in Fig. 1, was suspended in the middle of a room lined with wainscot, though this is not essential to the experiment. Four upright posts A, A, A, A, Fig. 1, are united at top by a cross rail BBB, and by two similar rails at bottom. This frame-work being placed on the floor, there proceed ed from the top of each upright post A, four bent cross wires a, a, a, a, which met together at the top c, where they terminated in a summit of any kind. From these four wires a hollow copper ball M, about a foot in diameter, was suspended by four slender ribbons b, b, b, b; and round this ball were placed four trum pets T, T, T, T, having their mouths opening exter nally.
When the spectator entered the apartment, he was called upon by the exhibitor to propose some question, which he did by speaking into the mouth of one of the trumpets T. When this was done, an answer imme diately issued from all the trumpets, sufficiently loud to be heard by an ear applied to any of them, and yet so weak that it seemed to come from a very diminu tive person. The invisible lady conversed in several different languages, sung beautifully, and made the most lively and apposite observations on whatever was going on in the room.
The method by which this deception was carried on is shown in Fig. 3. One of the posts AA, and one half TB of the hand-rail connected with it is hollowed into a tube, one end of which appears on the inside of the railing exactly opposite to the mouth of the trumpet T, while the other end communicated with a tube p p going below the floor f f, and passing up the wall to.a wide deal case h k, similar to an inverted funnel, and large enough to contain a lady with a piano forte. A small hole closed with glass, is left through
the funnel and side wall of the room about It, through which the lady may observe what is going on among the auditors.
When a question is now asked at the mouth of one of the trumpets T, the sound passes through the tube TAA p p it into the funnel hK, and is therefore dis tinctly heard by the lady. The answer likewise passes from the funnel along the tube It p p AAT, and strik ing the mouth of the trumpet, it is reflected back from it to the car of the auditor. The sound appears to issue also from every trumpet as the tubes commu nicate with each other.
6. On Ventriloquism.
In our article ACOUSTICS, we have given a short notice on the subject of ventriloquism; but as the ex planation there given is imperfect, though correct so far as it goes, it is proper to return to the subject.
The art of ventriloquism is founded upon a diligent study of the modifications which sounds undergo, when emitted under a variety of different circumstan ces; and, without a perfect knowledge of this part of his art, the ventriloquist will display his powers with little success. A sentence uttered by the same lips, and with the same intonation, behind a door shut or half open, or by a person enclosed in a box, or secret ed in the chimney, will obviously convey to those who hear it some idea of the locality of the person who utters it. If a ventriloquist, therefore, should have studied these modifications so completely, that he can pronounce the sentence with the precise modifications which the sound experiences, those who hear this sen tence must believe that it is uttered by a person in the chimney for example. In order, however, that this belief may be complete, the ventriloquist must turn his back upon his auditors, or must possess also the power of speaking with the muscles of his throat, so as not to move his lips, or alter the features of his face; for if any muscular action were seen in the face of the performer, it will be a vain attempt to impose upon the auditors, however nicely the sound be imi tated. The only conclusion would be, that the per former was an excellent imitator, but without any powers of deception.