Wireless Telegraphy and Telephony

IO WIRELESS TELEGRAPHY The electromagnetic waves have the power of exciting oscillations in a conductor on which they impinge. This is made use of for the purpose of receiving the messages. When the waves strike the aerial of a distant station they set up high frequency oscillations, which are usually too weak to make their presence known except with the aid of a sensitive device, called a detector. Fig. io.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound. The most prominent type of detector in use to-day is a crystal of silicon, iron pyrites, zincite or certain other min- erals. The mineral is placed between two contact points, one or both of which are adjustable so that the most sensi- tive portion of the mineral may be selected. A telephone receiver is connected across the terminals of the detector. When the electromagnetic waves from the transmitting sta- tion strike the aerial of the receiving station, they set up therein a series of high frequency oscillations, correspond- ing to the Morse signals emitted from the transmitter. The