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WHERE THE PUPIN COIL WORKS There are a hundred such on the line from New York to Chicago to build up the dying voice.

tions, installing new switchboards, hiring new and competent employes.

This talk is above all possible because these engineers have patiently experimented until they have found not one but three ways of forcing the voice along the long-distance wires, to distances quite out of the question two years ago. The particular instrument that today makes it possible to carry the voice so far over a wire is known as the telephone repeater. It is a voice builder. There have been other inventions found in company with this one to improve long-distance service, one of which is the open finder of Henry N. Bauer, by which it is possible to keep the wires up to maximum efficiency.

To understand the difficulty of pushing the voice to long distances, the reader must first understand that the means by which the voice is carried is one of the most subtle and uncertain known in

Ask a telephone engineer if there is an electric current used in transmitting the voice, and he will say "Yes". Ask him how great a current, and he will tell you that the tiny current used is so small, so weak, that it cannot be measured except with very delicate instruments. This current must be protected against many enemies. Every street-railway and electric lighting current is the enemy of the telephone. Then, rain. and sleet and snow and cold and heat are its enemies, too. Dust is its enemy. So are small boys with their kites and slings and mania for throwing things on the telephone wires. So are the bears in the wild country, which, looking for honey, cut down the poles, mistaking the hum of the wires for the buzz of bees. An Imperator, a Vaterland, an Olympic of the seas may steam into a harbor and sit on a cable, and another enemy of the telephone is found.

When a wire is laid in good condition, when the transmitters are perfect, when the smaller wires are insulated with enamel instead of silk and glass, as has just been done across the continent, when all is in working order, the long-distance chief has to contend with the fact that voice sounds tend to die out and waste away before they reach their destination. Take a fifty-foot rope, lay it along the ground, and then attempt to twirl it vigorously. The twirling movement becomes less violent in proportion as it travels along the rope. If a knot is tied in the middle of the rope, then the twirling movement picks up as it passes the knot and continues further along the rope. The voice acts in the same way on a wire.

A dozen years ago Michael J. Pupin, of Columbia University, New York, devised a means of tying knots in wires, that is, he reloaded them at intervals. This was a great step in long-distance work. There are some eight million miles of Bell telephone wire in the United States, and Pupin's invention, first valuable for revivifying the voice, made it

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The inside of a telephone office is apt to look somewhat untidy after King Winter has played havoc with

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The miles of wire that you see strung along the railways and the city streets do not comprise the total. There are rivers like the Hudson, the Mississippi, the Missouri, to be crossed in submarine cables.

Carty in the United States and Jacobs in England discovered that three messages could be run on two trunk wires at the same time, instead of two messages, if the trunks were crossed at intervals and perfectly balanced electrically. Three years ago the engineers discovered how to load No. 8 (long-distance) wires by the Pupin method and at the same time "to phantom" them, and by this discovery were enabled to make the two wires between Chicago and New York carry three messages. The phantom circuit

has already saved five or six million dollars. It made the New York to Denver

San Francisco talked to each other frequently, but in a jargon of telephonese that no untrained ear could understand. Then, suppose the line had been earlier opened to the public, and had to be shut again because of the need of making repairs? The public would have become disgruntled and declared the line non-existent.

Just a year ago, Bauer, who works in the myriad-wired testing distance department of New York, discovered a new way of detecting and locating exactly any unbalanced wire, that is, a wire that refuses to continue the talk-sound at

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