FIG. 116-Transmitting equipment of the high power station at Nauen, twenty-five miles northwest of Berlin, Germany, showing six induction coils (in the foreground) arranged to charge the Leyden jars (composed of 360 units).

Jars (composed of 360 units)

foreground) arranged to charge the Leyden

FIG. 117.-Duplex receiving apparatus. The set to the left may be adjusted to receive short wave
lengths and that to the right to receive long waves. When the handle of the "listening" key,
shown in the center of the illustration, is in the center, the left hand phone of the head set is con-
nected to the instruments on the left and the right hand phone to those on the right, so that the
operator is always ready to receive either short or long waves if received. Swinging the key con-
nects both phones to either set at will.

ΙΟΙ

former. Pressing the key, the operator then signals in the telegraph code J. H., J. H., J. H.—M. S. G.—N. Y.—and gives the "finish" signal. M. S. G. is the abbreviation for message. The N. Y. operator then throws his switch back into the receiving position and waits for a reply. If one is not forthcoming shortly the calling process is repeated.

As soon as the operator on board the steamer hears the call, he waits until the finish signal is received, and then

-J. H.

responds in the following manner: N. Y., N. Y., N. Y.— -O. K., O. K.—G. A.—G. A.—N. Y., J. H.-and gives the "finish signal." O. K. is the abbreviation for "all right," and G. A. means "go ahead." Upon receipt of this, the land station transmits the body of the message, and signs its call and finish signal. If the steamer understands the message, she replies "O. K.," and signs.

There are two Codes in general use for wireless telegraph purposes, the Morse and Continental. It takes about five per cent. longer space of time to send a message in Continental than it does in Morse, but the former has the advantage of not containing any letters requiring proper

spacing in order to be recognizable. American coastwise steamers use the Morse code; transatlantic ships use the Continental code.

One of the greatest disadvantages of most systems of wireless telegraphy lies in the fact that no arrangement is provided for simultaneously transmitting and receiving wireless signals. It is usually necessary for one operator listening to another to have to wait until the finish signal is given before he can reply or interrupt in case he cannot understand part of the message, because the receiving apparatus of the transmitting station is necessarily disconnected from the aerial and the ground during the period a message is being sent. If it were to be connected at this time the powerful currents of the transmitter would rush through the receiving apparatus into the ground without setting up any very powerful waves in the aerial and seriously injure the delicate receiving instruments.

The Breaking-in-System is a method of simultaneously transmitting and receiving wireless signals. This is accomplished by providing the transmitting key with a second set of contacts, so arranged that when the key is released between the dots and dashes of the code the aerial and ground are automatically connected to the receiving apparatus. When the key is pressed the receptor is automatically cut off. The advantages of such a system are more or less obvious. When interference or a misunderstanding occurs the fact can be immediately signaled to the sending operator, and the message commenced over again.