The system of operating wireless telegraphy is in some respects similar to that of the ordinary telegraph. The Morse Code is largely used in America, and a modification of it, called the Continental Code, in Europe. When the wireless operator wishes to send a message to another station he “listens in,” as it is called, by connecting his receiving apparatus with the adjacent antenna and the ground. He has the telephone receiver attached to his ears. Next he adjusts his receiving circuits for a number of wave lengths. If he catches no signals in his telephone receiver he understands that no messages are being sent within his area. Then he “throws in” the transmitting apparatus, which automatically disconnects the receiving end. He gives the letters that stand for the station with which he wants to communicate, and adds the letters of his own station. He does this a number of times, to insure the other station picking up the call. Then he “listens in,” and if he receives the clicks that show that the other station has heard him he is ready to establish regular telegraphic communication. A number of distant stations may be sending messages simultaneously. In that case the operator tunes his instrument, or in other words adjusts his apparatus to suit the wave length of the station with which he wishes to communicate. In this way he “tunes out” the other messages, and receives only the one he wants. If, however, the stations that are sending simultaneously happen to be situated near together, as in the case of several vessels near a shore station, the operator is often unable to do this “tuning out,” and must try to catch the message he wishes by the sound of the “spark” of the transmitting station, if he can in any way distinguish it from the “sparks” of the other messages. There are several ways of determining when the two circuits are in tune. One is to insert a hot-wire current meter between the antenna and the inductance, which indicates the strength of the oscillatory current that has been established. A maximum reading can then be made by manipulating the flexible connections, and this will show whether the two circuits are in accord. The other method is by using a device that indicates the wave length. This measures the frequency of one circuit, and then the other circuit can be adjusted to give a corresponding wave length. The larger the antenna the longer will be the wave length and the greater the power of the apparatus. It is usual to employ a short wave length for low-power, short-distance equipments, and a long wave length for the high-power, long-distance stations.