Telephone Plant in the United States

Dial Telephones.--As

progress was made in the improvement of manually operated switchboards, the tendency was constantly toward the substitution of automatic devices for human labour. The accomplishments in this direction became more marked after the introduction of common battery operation with lamp signal ling. After a time, so much progress in this direction had been made that the question began to be raised whether ultimately in large cities it might not be possible to eliminate the operator entirely by the substitution of electrically controlled machinery. The development of automatic switching has paralleled that of other forms of switchboard. Basically, all forms of automatic switching involve the substitution of electrical impulses for the voice of the subscriber in making known his desires and the use of electrical machinery instead of human operators at the central office as the means for interpreting these desires and performing the desired switching operations. Modern panel type automatic switching equipments such as are employed in great metropolitan areas are so complex as to require the concentrated attention of specialists for their comprehension. All that can be attempted here, therefore, is merely an outline of some of the major steps. U.S. patents covering an automatic switching system were first applied for in 1879, but the system which they described never became a commercial success. In 1889, however, A. B. Strowger, invented a system which was subsequently improved by others and is used successfully at the present time under the name of "step-by-step" system. Other automatic systems containing im portant features contributing greatly to the success of automatic switching appeared both in America and abroad.

The Bell System became actively engaged in the development of automatic switching equipment prior to 1900. In its desire to perfect and simplify the operation of switching in every practicable way, it sought to determine fundamentally the type of machinery best suited to the needs of a universal service. As a result of pro tracted and searching inquiry, a large installation of automatic equipment was made in 1914. In this, the central office equipment was of the so-called "panel" type. The installation was designed not as a final test of a complete automatic system but as a trial on a large scale of the efficacy of the machinery which seemed most likely to give the desired results when applied to a complete automatic system. In this trial, the subscribers called the operators in the usual manner but from the operator onward, the connection was completed entirely by the use of automatic switches. As a result of this and subsequent modifications, the details of the panel system were perfected. The first exchange giving complete automatic operation with panel type switches was installed in 1921.

Since that time, the application of dial telephones has grown rapidly until in about 4r per cent. of the telephones in the United States are operated on a dial basis, through either panel or step-by-step switches. Plate II., fig. I, shows a portion of dial operated central office equipment. Before dial systems could be widely employed they not only had to work properly within themselves, but means had to be devised whereby they could also be made to work successfully in conjunction with existing manu ally operated systems.

The foregoing are but a few of the many improvements brought about by development and research. Among others may be men tioned "carrier" telephony, by means of which more than one telephone conversation can be carried on simultaneously over a single line ; transatlantic telephony by means of whiCh service is now possible between America and large portions of Western Europe; and telephotography, which enables pictures to be re produced at distant points.

Extension of Long Distance Communication.

The first "long distance" conversation took place in 1876 over a line two miles in length between Cambridge and Boston, Mass. Conver sation by telephone became possible in 188o between Boston and Providence, R.I., and in 1884 between Boston and New York. The long distance lines reached Chicago in 1892 and in 1911 were extended to Denver, Colo. Salt Lake City was connected

with the Eastern Seaboard in 1913. In 1915 the first transcon tinental telephone line was opened between New York and San Francisco. As public demand for long distance service grew greater, a second line across the country became necessary and in 1923 a southern transcontinental line was opened to service through New Orleans, La., and El Paso, Tex., to Los Angeles, Calif. A third line across the continent was opened in 1927 by way of Minneapolis, Minn., to Seattle, Wash., and Portland, Oregon. A fourth line was established in 193o between St. Louis and Los Angeles using a route somewhat north of the southern transcontinental line in passing through Holbrook and Kingman, Arizona. The reliability of the long distance telephone service has been substantially enhanced of late years by the placing of many of the important lines in aerial or underground cables which are practically storm-proof. Out of a total of about 80,425,000 miles of Bell System telephone wire on Sept. 30, 1935 (consisting of 65,119,000 miles of exchange wire and 15,306,000 miles of toll wire), 66% or 52,644,00o miles, was in underground cable; about 29%, or 23,209,000 miles, was in aerial cable; and the remainder, miles, was in open wire.

A

large part of the most highly industrialized sections of the United States is now covered by the spreading network of tele phone cables shown in Figure 2. The cable network extends up and down the Atlantic seaboard from Bangor, Maine, to Atlanta, Georgia. It extends westward through Chicago and St. Louis and intermediate points to Omaha and Kansas City, in the Southwest to Cisco, Texas, 140 miles west of Dallas, and in the Northwest it extends through Wisconsin cities to Stevens Point, Wisconsin. Telephone messages can now be transmitted entirely through cable from Bangor, Maine in the Northeast to Atlanta, Georgia in the South, 1,33o miles; to Cisco, Texas in the South west, 2,450 miles; and to Omaha in the West 1,800 miles. In the New York-Pittsburgh section of the route between the Atlantic seaboard and the West, the present cables, when utilized to capac ity, will provide facilities for Boo telephone conversations and at least as many telegraph messages simultaneously. This route, with an average of four cables, involves 1,069 miles of aerial cable and 385 miles of underground cable. The total weight of cable is 65,000,000 pounds and it consists of about 16,000 sections having Io,000,000 wire splices.

Chicago and New York are connected by telephone cable routes : (I) New York-Pittsburgh-New Castle-Cleveland-South Bend-Chi cago.

(2) New York-Pittsburgh-Wheeling-Indianapolis-Terre Haute-Chi cago.

(3) New York-Albany-Buffalo-Cleveland-South Bend-Chicago.

Canada was brought into communication with the United States many years ago and now the eastern toll cable network extends to Montreal and Toronto. Three telephone cables under the Flor ida straits between Key West and Havana were opened to service in 1921 making it possible to talk between the North American continent and Cuba. A fourth cable of increased message capacity was placed in service in 1931. In 1927 communication was made with land lines reaching to principal cities of Mexico. Transat lantic telephone service was opened in 1927 through co-operation of the American Telephone and Telegraph Company and the British Post Office. Circuits were added in 1928 and 1929 so that now a group of four transatlantic circuits are available be tween New York and London connecting with all points in the United States and most of Europe. In 1931 radio stations were established on the Pacific Coast which now furnish service be tween the United States and the Hawaiian Islands, Philippine Islands, Netherland Indies and Japan. Facilities established in New Jersey in 193o and at Miami in 1932 provide service between the United States and most of the countries in Central and South America. At present, regular service is given between the United States and 67 other countries throughout the world. Any Ameri can telephone may be connected with any one of 93 per cent. of all telephones in the world.