Page:Popular Science Monthly Volume 12.djvu/584

566 expressed by the word induction. Briefly, it may be put thus: that, when a strong electric current is passing on a wire, it has the faculty of setting up a current of opposite character in any wire not then working, or working with a feebler current, that may be in its vicinity. The why or the wherefore cannot be explained, but there is the fact.

"In various recent articles on the telephone, mention has been made of 'contact' as the cause of disturbance. This word, however although it has been used by telegraphists, is misleading, and can only be used as an endeavor to express popularly an electric fact. Actual contact of one wire with another would spoil the business altogether. A wire bearing an electric current seems to be for the time surrounded, to an undefined distance, by an electric atmosphere, and all wires coming within this atmosphere have a current in an opposite direction set up in them. This is as near an explanation of the phenomena of induction as the state of telegraph science at present affords. Now, the telephone works with a very delicate magnetic current, and is easily overpowered by the action of a stronger current in any wire near which the telephone-wire may come. To work properly, it 'requires a silent line.'

"In the place where the observations were made, there were a large number of wires traveling under the floor, along passages to the battery-room, and to a pole on the outside, whence they radiate, or out to a pipe underground, where many gutta-percha-covered wires lie side by side. On applying the ear to a telephone joined into a circuit working in such an office, a curious sound is heard, comparable most nearly to the sound of a pot boiling. But the practised ear could soon separate the boiling into distinct sounds. There was one masterful Morse instrument—probably on the wire lying nearest the one on which we were joined up—whose peremptory 'click, cli-i-i-ck, click,' representing 'dot, dash, dot' on the printed slip we read from, could be heard over all. Then there was the rapid whir of a fast speed transmitter sending dots and dashes at express speed by mechanical means; and, most curious of all, the 'rrrrr-op, rr-op, rrrrrrr-rrrrrr-op, rrrrr-op, rr-op' of the A B C, or printing-instrument, the deadliest foe to the telephone in its endeavors to gain admission into the family of telegraph-instruments. There may be reason in this, for as the ABC, or printing-instrument, is the instrument used for private telegraphy, or for the least important public offices, because it requires no 'code' to be learned by the manipulator, so it would likely be the first to be displaced if an acoustic telegraph permanently took the field. So the sentient little ABC opens its mitrailleuse-fire on the intruder, on whose delicate currents, in the words of an accomplished electrician, it plays 'old Harry.' The peculiar character of the sounds we borrow on the telephone from this instrument arises from the fact that, as the needle flies round the dial, a distinct current