Page:Popular Science Monthly Volume 12.djvu/585

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THE TELEPHONE AND HOW IT WORKS.

or pulsation passes for each letter, and the final 'op' we have tried to represent shows the stoppage of the needle at the letters as words were spelled out.

"It must not be understood that the sounds of those various instruments are actually heard in the telephone. What happens is, that the currents stealing along the telephone-wire by induction produce vibrations in the diaphragm of that instrument, the little metal membrane working on the magnet in ready response to every current set up the latter. When it is remembered that the principle of the telephone is that the sound-caused vibrations in the filmy diaphragm at one end create similar but magnetically-caused vibrations in the diaphragm at the other end, and so reproduce the sound, it will be obvious why the rapid roll of the ABC currents, or the swift sending of the fast-speed transmitter, when brought by induction into the telephone-wire, cause disturbances in the sound-vibrations, and thereby cripple the instrument. One instrument of either kind named would have a certain effect, but one Morse would not have any greatly prejudicial effect. But a number of Morses going together, such as were heard in our experiments, would combine to be nearly as bad as one A B C or fast-speed Morse. So delicate is the diaphragm to sound (and necessarily so) that, in all experiments with the telephone itself, every sound from without broke in, giving an effect like the well-known 'murmur of the shell.' "

"Joining up our wire now to a more distant station at some miles along the railway, and having on its poles a number of what are known as 'heavy' circuits, the pot-boiling sound assumed even more marked characteristics. The A B C no longer affected us; but a number of Morse instruments were in full gear, and the fast-speed transmitter was also at work. While we were listening, the circuit to which we were joined began to work, and the effect was literally electrical. Hitherto we had only borrowed currents—or, seeing they were so unwelcome, we might call them currents thrust upon us—and the sounds, though sharp and incessant, were gentle and rather low. But, when the strong current was set up in the wire itself, the listener who held one of our telephones nearly jumped from the floor when an angry 'pit-pat, ’pit-pat, pit-pat-pit' assailed his ear, causing him to drop the instrument as if he had been shot. It was a result none of us had expected, for it did not seem possible that the delicate metal diaphragm and the little magnet of the telephone could produce a sound so intense. Of course, it was only intense when the ear was held close to the orifice of the instrument. Held in the hand away from the ear, the telephone now made a first-rate 'sounder,' and we could tell without difficulty not only the signals that were passing, but found in it a more comfortable tone than that given by the Morse sounder in common use.

"Other experiments of a like character led to results so similar