Page:The American Cyclopædia (1879) Volume XV.djvu/650

 621< TELEPHONE Transactions " of 1758 ; the vertebra were 64, 16 being dorsal, and the teeth about 70 in each jaw ; some of the dermal plates were 3 Teleosaurus Cadomensis. in. in their transverse diameter; it attained a length of about 13 ft. The name has been generally restricted to the species found in the oolite, especially the T. Cadomensis (fit. Geoffr.), or crocodile of Caen, from the lime- stone of Normandy. This is characterized by large orbits near together, a flattened muzzle five times as long as wide, very long transverse processes of the dorsal vertebra, and thick rectangular scales forming 10 regular series, each containing 15 or 16; it must have at- tained a length of 20 ft. TELEPHONE (Gr. rayAe, afar, and favhv, to speak), an apparatus for transmitting sounds to a distance, through the agency of electricity. The principle of the magnetic telephone de- pends upon two things: 1, that a thin soft-iron plate, placed in a confined position, as in an ar- tificial ear, will be thrown into vibrations by sound waves, just as the tympanum of the nat- ural ear is affected by similar waves; and*2, that if these vibrations are produced near one end of a steel magnet around which an insulated wire is coiled, a magneto-electric current will run through the wire each time that the iron plate approaches and recedes from it. If this wire be carried to a distance and coiled around a second magnet, the electric current thus in- duced will simultaneously affect the magnetism in it ; and if a thin iron plate, similar to the first, be placed near its end, in the same rela- tive position as the one in front of the first magnet, the vibra- tions of the first plate will be reproduced in the second. To recapitulate: In the human ear sound waves induce vibrations in the tympanum, and these vibrations are conveyed to the auricular nerves through a se- ries of small articulated bones. In the telephone similar waves cause vibrations in a soft-iron disk, called the diaphragm; these vibrations induce electric currents, which, passing through wires, cause tremors in a second magnet, and these reproduce in a second diaphragm the original vibrations, which carry to the tym- panum of the listener the exact sounds which produced the vibrations. As the instruments at each end of the wire are precisely alike, the action is reciprocal, and sounds may be con- veyed in either direction. The construction of the telephone will be best understood by a ref- erence to the diagram, fig. 1. In this, b & rep- resents the section of a thin tube, made with a flange which bends outward. Next to this flange is a thin iron plate, cc, which constitutes the diaphragm of the instrument, and which is thrown into vibrations by the sound waves. A wooden ring or washer, dd, is placed next to this, and upon it a spool-shaped tube, e e, just large enough in the barrel to admit the mag- netized steel rod g. The parts may be screwed up tightly together, by means of the screws hh. The mouthpiece, a, is shaped like a fun- nel, so that the voice may be concentrated on a small part of the diaphragm. Around the spool is wound about 50 yards of fine silk-covered copper wire, the ends of which are joined to the line wires, ff. These connect with another precisely similar instrument at a distance from the first. To operate the telephone, the mag- net is pushed in until it nearly touches the diaphragm, cc. Any sound now made in the mouthpiece, a a, causes a vibration in the di- aphragm, cc, which is communicated to the magnet, and through it to the wires. The latter convey the thrill to the magnet of the second instrument, which in turn causes vibrations in its diaphragm, and this reproduces the sound waves which caused the vibrations in the first instrument. Thus the sounds made in the mouthpiece of the first instrument are con- veyed over miles of wire, and reproduced so accurately by the second instrument that the words of a speaker may be distinctly heard, and even the tones recognized. Conversation has been carried on through the telephone by persons 300 miles apart. Sounds have been conveyed much further ; but beyond that dis- tance the articulation is so indistinct that words are unrecognizable. In using the telephone, the instrument is held close to the lips, and the FIG. i. speaker talks loudly and distinctly into the mouthpiece. The words are repeated at the other end of the circuit with the same pitch