But how can these signals be received by the man for whom they are intended, who may be a hundred miles or more away? He has a "receiving" set, consisting of a sensitive relay, batteries, resistance-coils, a Morse register, an aerial, and a special device called a "coherer." This is the important part of the whole set, because it is sensitive to the electrical waves. It consists of a little glass tube about as large around as an ordinary lead-pencil, and perhaps two inches long. In the tube are two metallic plugs, each having a wire attached so that one wire projects from each end of the tube. The plugs are separated inside the tube by a very small space, and in this space are some metal filings. One wire from the coherer is connected to the aerial and the other to the ground. When there are no electrical ether waves to influence them, these filings, being loosely separated, are at rest and offer high resistance; but when the ether is disturbed by electrical vibrations and the waves arrive at the coherer (through the aerial), these filings are drawn together, or cohere. This lowers their resistance and they become a better conductor. Now, the coherer wires are also connected through a battery to the relay, which in turn is connected through another battery to a Morse register. Therefore, when the filings become a conductor, the current flows through them and the circuit to the relay is closed. That attracts an armature which closes the circuit of the Morse register and thus marks the electrical impulse on a strip of paper tape. In the mean time, a restoring device, called a "decoherer," operated also by the relay circuit, has tapped upon the coherer, thus shaking the filings loose again, so that they are ready to cohere again and register another impulse, or character. Thus, by pressing the key at the transmitting end for long or short periods, to represent Morse characters, long and short waves are propagated in the ether and are received and recorded at the receiving end through the coherer and other parts of the receiving set. In this way telegraphic messages are sent and received through space, between points separated by hundreds or thousands of miles.