Telephone
an instrument for transmitting sounds or speech to distances aërial sound waves. This definition exa cludes speaking tubes, which act simply waves. Telephonic action depends on the fact that sound waves in air are capable of communicating vibrations to stretched membrane, and if by any means such vibrations can be transmitted with true resemblance to another membrane at any distance, such receiving membrane will reproduce the sound. This capacity of a single vibrating membrane to reproduce the most complicated sounds, as of speech, is in reality the greatest mystery connected with the matsounds, as of speech, is in reality the of transmission only. The essential nature of the operation is weli shown in the common toy telephone sold in the streets, in which the floors of two small tin cups consist of stretched membranes, or even of paper. The two membranes are connected by a long piece of twine. If now one cup be held to the mouth and spoken into, the voice communicates vibrations to the membrane. The stretched twine communicates similar vibrations to the membrane of the other cup, and if its cavity be held to the ear the sounds will The true inventor of the first telephone was undoubtedly Philip Reis, who showed, in 1861, that variations in an electric current caused by a vibrating membrane could reproduce the necessary vibrations.
Reis in this way transmitted musical served for Alexander Graham Bell to perfect that which is still commonly used and known as the Bell telephone, though electricians that Bell's patent has been held by courts of law to cover far more ground than is really due to him, much to the public detriment and to the hinthere is a cylindrical steel magnet, surthere is a cylindrical steel magnet, surends are connected by wire with the cirends are connected by wire with the cirstood that any change in the power of the stood that any change in the power of the magnet will cause currents in this wire.
Near, but not touching, the magnet's end is stretched a very thin sheet of iron, as a membrane, which is spoken to through the iron membrane approaches to and recedes from the magnet; and as it acts close the magnetic circuit, the effect is to produce fluctuating degrees of free magnetism, which again produce flucture. But if these fluctuating currents ating or undulating currents in the line wire . are received in a precisely similar instrument, they in its coil produce variable magnetic force in the magnet, and this reproduces vibrations in the second iron membrane, which reproduce the sound.
The second class of instruments are a galvanic current is composed of two based on the microphone. If part of or three pieces of matter (preferably variations in the concharcoal) in loose contact, variations in the current produce va tact pressure of the loose pieces, and the converse. Hence, instead of a vibrating membrane causing undulating currents by means of a magnet as in the Bell of mere contacts, and thus cause an unof mere contacts, and thus cause an unis capable of converse action. A microphone is thus capable, with more or less modification, of being used as a telephone, and the employment of either method is a question of practical conditions. The Bell telephone is independent of any battery, being self-acting; TELEPHONE but its feeble currents are incapable of transmitting speech to a distance; hence most of the modifications in magnetic telephones have had the design of increasing the power, as by using both poles of the magnet, and in other ways.
The microphone, on the other hand, uses the power of a battery in its circuit, but in some respects appears less delicately sensitive than the free membrane. In practice it is very general to employ some form of microphone as the transmitting or speaking instrument, and the Bell telephone, or one of its modifications, as the receiving or hearing instrument.
There are now many forms of telephone in use, the principal varieties being the bi-telephone, in which there are two receivers, one for each ear; the capillary telephone, in which electro-capillarity is used to produce telephonic effects; the chemical telephone, in which chemical or electrolytic action is utilized; the electrostatic telephone, which utilizes electrostatic disturbances in the reproduction of sound; the reaction telephone, in which two mutually reacting coils are used; and the thermo-electric telephone, in which a thermo-electric battery is used. The last-named telephone has never been used in practice. In 1892 a long-distance telephone was erected between Chicago and the larger E. cities and such service has been extended everywhere. In 1902 a patent was obtained in the United States for a wireless telephone service. De Forrest and others have since filed many patents. In 1915 the American Telegraph and Telephone Co. sent a message from Washington to Paris without wires and subsequently from Washington to Hawaii. Portable telephones were largely used in the World War.
See WIRELESS TELEGRAPHY AND TELE- PHONY.