TELEPHONE (from Gk. TOE, Ulc, afar --I cpcoph, pkonC., voice, sound). An instrument for the transmission of speech or musical or other sounds by means of electrical vibrations corre sponding to the original sounds. The first use of the word telephone is in a description of ex periments by Wheatstone where sound was trans mitted through wooden rods. In 1337 Page, of Salem, Mass., noticed that an iron rod suddenly magnetized and demagnetized would emit certain sounds which were due to a rearrangement of the molecules, and this phenomenon has since been known as Page's effect. Bourseul of France in 1854 conceived the fundamental idea of the telephone, but did not, however, put it into actual practice. He proposed a device in which a cur rent interrupted by a vibrating disk under the influence of the voice would produce a similar vibration of a disk at the end of a conductor through the agency of an eleetro-magnet. In 1860 Philipp Reis, of Frankfort, invented an ap paratus which he named 'Telephone,' with which he was able to reproduce sound at a distance. Reis's telephone, about which there has been much controversy, in his hands at least was able to transmit articulate speech, and he is entitled to credit for the principle of the instrument. For the practical development of the idea and the in vention of an actual working telephone the honor must be given to Alexander Graham Bell, who, March 7, 1876, received letters patent for new and useful improvements in telegraphy in which a method for the transmission of vocal sounds is one of the most important of the claims. Few patents for inventions have been subject to more litigation than the telephone, and the literature on the subject it quite exhaustive; but Bell's rights have been su4tained by the highest courts. and though he was closely followed by other in ventors, notably Elisha Gray, he may fairly be entitled to the honor of the invention.
The Bell telephone, which has survived as the modern receiver, served both as transmitter and receiver in the early apparatus. A referenee'to the accompanying diagram showing a cross sec tion of a modern unipolar receiver will make clear its action. There is a hard rubber ease hol lowed at its upper extremity and containing the soft iron diaphragm about inch thick and two and a quarter inches in diameter, with free part one and three-fourths inches across, which is tightly held at its circumference, but its centre is free to vibrate. A bar magnet, either single or
compound, carries at its upper end a coil of fine silk-covered wire (No. 33 B. & S. gauge general ly) with resistance of about 75 ohms, whose ter minals connect with the binding posts. A more powerful receiver can he constructed by employ ing instead of a single magnet a horseshoe mag net with coils on each pole. In the Ader bipolar receiver, used extensively in Continental Europe, the horseshoe magnet is ring-shaped and outside of the diaphragm, and in front of the pole pieces a soft iron ring is placed with the object of strengthening the field of force between the poles. The diaphragm of a telephone receiver is in close proximity to the pole or poles of the magnet. but not in contact. When used as a transmitting instrument thi5,' diaphragm will vibrate under the influence of the voice, its movement being caused by the movement of the air known as sound waves. The diaphragm rapidly approach ing and receding from the magnet consequently produces currents by induction in the wire of the coil. These currents will be transmitted over the line wire, and. flowing through the toil of the re ceiving instrument, will cause its magnet to be come more strongly magnetized and the dia phragm to be attracted. The diaphragm of the receiver will accordingly move in unison with that of the transmitter, and consequently the sound wave which impinges on the latter will be reproduced. The ground can be used as a re turn or the circuit can be of wire throughout. The currents of electricity that were transmitted in this way were too feeble to produce satisfac tory sounds at the receiving instrument when there was a line of any considerable length, and it was necessary to find a better transmitter. Accordingly there followed the carbon transmit ter, where the change of resistance of carbon un der pressure produces pulsations in the current corresponding to the vibration of the sound waves.