SPEAKING TUBES. Instruments for enabling the human voice to be heard at a great distance appear to have been known to the ancient Chinese. The modern speaking trumpet appears to have been an invention of Sir Samuel Morland, in the year 1070. This first trumpet was of glass, 2 feet 8 inches long ; and he afterwards made one of copper, re curved in the form of a common trumpet. Its total length was 10 feet 8 inches, the large end 19 inches, and the small end 2 inches in diameter. With this the voice was heard about a mile and a half. Morland made another of the same form, still larger, and two others of the straight form, and 5 feet and a half long. With the latter a man could make himself heard a mile and a half; and with one of the largest trumpets, tried at Deal Castle, the voice was conducted a distance of between two and three miles over the sea.
The efficiency of the speaking-trumpet is generally ascribed to the repeated reflection of the sound from side to side in passing through it, and its ultimate reflection from the mouth of the trumpet, in such a way as either to collect the rays of sound into a focus at a dis tance, or to project them forward in parallel lines, instead of allowing them to diverge in all directions. But Sir John Leslie accounts for its effect in the following manner: The tube, byits length and narrowness, detains the efflux of air, and has the same effect as if it di minished the volubility of that fluid, or in creased its density.' The organs of articula tion,' he continues, ' strike with concentrated force ; and the pulses, thus vigorously excited, are from the reflected form of the aperture, finally enabled to escape, and to spread them selves along the atmosphere.' The effect of a speaking,-trumpet is the same, whether the metal tube he used simply, or wrapped round in such a way as- to prevent vibration. It is also heard at the same distance when the inner surface is lined with linen or woollen cloth to di minish reflection ; and the range of a cylindri cal trumpet is the same as that of a conical one.
The most valuable speaking tubes, how ever, are not • those -which are intended to convey sound to a- great distance, but those intended to aid persons whose dense of hear ing is defective. Something has been said on this subject under ACOUSTICS. The prin ciple of the SONIFERON, described in that article, pervades all instruments of this kind ; they collect and concentrate the waves of sound, so as to make them impinge upon the tympanum of the ear with greater force..They. are in principle .the reverse of the speaking trumpet; for in this the sound proceeds from. the small end. to the larger, whereas in speak ing tubes ur ear trumpets it proceeds from the largo end to the small. Many varieties are made,.under the names of auricles, ear-carnets, car-coimlies, .cofirenalion-iubcs, table-soniferas, •84e, adapted to different requirements _of parr tially deaf persons. See also SONOMETER..
It has lately been found that gutta percha so invaluable for many other purposes-is the best of all materials for speaking tubes, since it conveys the pulses of sound with surprisingly little diminution of intensity. In churches, in ships, in warehouses and factories, and. in various other buildings and places, guttapercha speaking tubes are now used to a considerable extent, The mode of applying these tubes to the assistance of partially deaf persons in a church is curious. A funnel of the material is placed either.inside the pulpit, quite.out of sight, or, if ornamented, in front of the pulpit, so as to come immediately beneath the desk. A tube from this funnel then passes down wards beneath the floor, and is carried along the aisles, with branches off on each side to the pews occupied by people of defective hearing. The termination of the tube is all that appears in sight, and the ivory ear-piece being applied to the ear, the slightest whisper of the preacher is clearly heard.