Page:Popular Science Monthly Volume 9.djvu/93

Rh The germ of the automatic system, as we have described it, was contained in the "Chemical Telegraph" invented by Alexander Bain, a Scotchman, in 1846. Bain was the first to use the perforated paper to transmit and the chemically-prepared paper to receive the message. But his invention, from a practical point of view, bears about the same relation to the American system which the steam-engine as known to the ancients does to that of James Watt. Bain's system, improved by the late Sir Charles Wheatstone and known as Wheat-stone's automatic system, is employed to a limited extent in Great Britain; but, thus improved, its speed does not exceed 60 to 100 words a minute. It is therefore proper to regard the American Automatic Telegraph as a distinct American invention. In its present form, we owe it to Mr. Thomas A. Edison, of Newark, New Jersey.

The accompanying cut (Fig. 4) illustrates the results of attempting



high speed on the Bain telegraph. Instead of recording themselves by decided dots and dashes, the electric discharges leave indistinct and elongated traces, which, when the speed amounts to 300 words or over, run into one another and make a continuous line. This effect is due to the property which all electrified bodies have of inducing electricity in neighboring bodies. The earth, reacting on the line wire suspended above it, induces in it what is called an extra current, both on closing and breaking the circuit. On first closing the circuit the extra current runs in the contrary direction to the primary, and retards and weakens its action, so that, if suffered to record itself, it would do so by a mark like this: the long after-part being caused partly by the accumulated electricity and partly by the second extra current which is in the same direction with the primary one.



By Mr. Edison's plan the evil is made to cure itself. He simply interposes another wire with a coil, shown at A C E, (Fig. 5). This divides the current, one part of which is again subdivided on