Assoc. Report), when he drew attention to the considerable distance over which inductive effects occurred between parallel wires forming portions of telephonic and telegraphic circuits.
Heaviside in 1887 succeeded in communicating by telephonic speech between the surface of the earth and the subterranean galleries of the Broomhill collieries, 350 feet deep, by laying above and below ground two complete metallic circuits, each about 24 m.
In 1885 Preece and Heaviside proved by experiments made at Newcastle that if two completely insulated circuits of square form, each side being 440 yds., were placed a quarter of a mile apart, telephonic speech was conveyed from one to the other by induction, and signals could be perceived even when they were separated by 1000 yds.
Telephonic speech between these two circuits was found possible and good, the communication between the circuits taking place partly by induction, and no doubt partly by conduction.
By stretching on the island and mainland parallel wire circuits earthed at each end, good telephonic communication over an average distance of 62 m.
An exchange is a central station to which wires are brought from the various subscribers in its neighbourhood, any two of whom can be put in telephonic communication with each other when the proper pairs of wires are joined together in the exchange.
Although the bells are constantly in circuit their high impedance prevents any appreciable interference with the telephonic currents.
In circuits possessing high resistance and capacity and low inductance per mile, telephonic currents are rapidly attenuated, and the higher the frequency the more rapid is the attenuation.
In consequence of their high capacity, the attenuation constant of submarine cables is high, and only a small number of cables, of comparatively short length, are in use for telephonic purposes.
In 1885 there were only 3800 telephone subscribers in London and less than io,000 in the rest of the United Kingdom, and telephonic services were available in only about 75 towns, while in the same year the American Bell Telephone Company had over 134,000 subscribers.
There are now four circuits between London and Paris, one between London and Lille, and two between Londofi and Brussels, the last carrying an increasing amount of traffic. Experiments have been made in telephonic communication between London and Rome by way of Paris.
All the railway lines, like the postal, telegraphic and telephonic services, are state property.
The National Telephone Company, working under licence expiring on the 31st of December 1911, had until 1901 practically a monopoly of telephonic communication within London, though the Post Office owned all the trunk lines connecting the various telephone areas of the company.
Signor Rosio used a telephonic method to effect the same end, and mechanical, optical and telephonic devices have been utilized by the Rev. F.
The telephonic systems of Guatemala la Nueva, Quezaltenango and other cities are owned by private companies.
There is a complete telegraphic and telephonic service.
The state revenue is derived from customs; from public works and public land; from indirect taxes in the shape of stamp, inheritance, beer, spirit, petroleum and other duties; from direct taxes on land and buildings, with road-tolls, licences for the sale of alcohol and traders' registration fees; from the tobacco, salt, match, playing-card and cigarette-paper monopolies; and from the postal, telegraphic and telephonic services.
There is also a telephonic service, the longest line being from Harrar to the capital.
Alexander Graham Bell in 1876 invented the speaking telephone, and Edison and Elisha Gray in the United States followed almost immediately with other telephonic inventions for electrically transmitting speech.
Nicaragua joined the postal union in 1882, and the western provinces have a fairly complete telegraphic and telephonic system.