Every wireless station on land or sea has assigned to it two or more "call letters," which distinguish it from all other stations, and serve as the key to messages intended for it to receive and when signed to a message as an indication of its origin. The "call" of the land station in this case is N. Y., and that of the steamer, J. H.
FIG. 115.—Continental code.
In order to send the message to the ship, N. Y. throws the aerial into position for sending. This act also starts the motor generator set supplying current to the transformer. 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.
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).
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 connected 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 connects both phones to either set at will.
As soon as the operator on board the steamer hears the call, he waits until the finish signal is received, and then responds in the following manner : N. Y., N. Y., N. Y.—J. H.—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.
