The Wonder Book of Knowledge / The Marvels of Modern Industry and Invention, the Interesting Stories of Common Things, the Mysterious Processes of Nature Simply Explained

by Unknown

The First Transcontinental Line.

The opening of the first transcontinental line between New York and San Francisco on January 25, 1915, was an epoch-making event in telephone history. The line is 3,400 miles long. It crosses thirteen states; it is carried on 130,000 poles. Four hard-drawn copper wires, .165 of an inch in diameter, run side by side over the entire distance, establishing two physical and one phantom circuit. The ordinary telephone connection consists of two wires technically called a telephone circuit, each wire constituting one “side” of the circuit. A phantom circuit is a circuit superimposed on two ordinary circuits by so connecting the two wires or “sides” of each ordinary circuit that they can be used as one side of the phantom circuit. In this way three practical talking circuits can be obtained from four wires. One mile of single wire used in the transcontinental line weighs 435 pounds, the weight of the wires in the entire line being 5,920,000 pounds, or 2,960 tons.

This Picture Shows the Difficulties Encountered in Hauling Poles in a Mountainous Section Along the Transcontinental Line of the Bell System

In addition to the transmission wires, each circuit uses some 13,600 miles of fine hair-like insulated wire .004 of an inch in diameter in its loading coils.

It was, perhaps, little more difficult to string wires from Denver to San Francisco than from New York to Denver, but the actual construction of the line was the least of the telephone engineer’s troubles. His real problem was to make the line “talk,” to send something 3,000 miles with a breath as the motive power. In effect, the voyage of the voice across the continent is instantaneous; if its speed should be accurately measured, a fifteenth of a second would probably be nearly exact. In other words, a message flying across the continent on the new transcontinental line, travels, not at the rate of 1,160 feet per second, which is the old stagecoach speed of sound, but at 56,000 miles per second. If it were possible for sound to carry that far, a “Hello” uttered in New York and traveling through the air without the aid of wires and electricity would not reach San Francisco until four hours later. The telephone not only transmits speech, but transmits it thousands of times faster than its own natural speed.

But while the telephone is breaking speech records, it must also guarantee safe delivery of these millions of little passengers it carries every few minutes in the way of sound waves created at the rate of 2,100 a second. There must be no jostling or crowding. These tiny waves, thousands and thousands of varying shapes, which are made by the human voice, and each as irregular and as different from the other as the waves of the sea, must not tumble over each other or get into each other’s way, but must break upon the Pacific coast as they started at the Atlantic, or all the line fails and the millions of dollars spent upon it have been thrown away. And in all this line, if just one pin-point of construction is not as it should be, if there is one iota of imperfection, the miles of line are useless and the currents and waves and sounds and words do not reach the end as they should. It is such tremendous trifles, not the climbing of mountains and the bridging of chasms, that make the transcontinental line one of the wonders of the ages.

The engineer in telephony cannot increase his motive power. A breath against a metal disk changes air waves into electrical currents, and these electrical currents, millions of which are required for a single conversation, must be carried across the continent and produce the same sound waves in San Francisco as were made in New York. Here is a task so fine as to be gigantic. It was to nurse and coax this baby current of electricity 3,000 miles across the continent, under rivers and over mountains, through the blistering heat of the alkali plains and the cold of snow-capped peaks, that has taken the time and thought and labor of the brightest minds of the scientific world.

This great problem in transmission was due to the cumulative effect of improvements, great and small, in telephone, transmitter, line, cable, switchboard and every other piece of apparatus and plant required for the transmission of speech.

The opening of the transcontinental telephone line has been followed by the extension of “extreme distance” transmission into all the states of the Union, by applying these new improvements to the plant of the Bell System. It is now possible to talk from points in any one state to some points in every other state of the Union, while over a very large part of the territory covered by the Bell System, it is possible for any subscriber to talk to any other subscriber, regardless of distance.