positions (besides the upright one) by a single movement of each hand, as may be seen in fig. 249; and these eight signals if repeated, or made twice in rapid succession will make eight more, and by being repeated three times will constitute a third eight, making twenty-four; finally, by a rapid motion right and left, they may be caused to signify a fourth eight, or thirty-two signals, which are found to be sufficient for every purpose, and by practice may be both produced and read off with facility. Before a message is about to be delivered the commutator is so placed as to ring a bell, which is done by the same arrangement as in a common alarm-clock, but the action is set in motion by a peculiar contrivance, which depends upon the property a bar of soft iron has of becoming magnetic when a wire is wound round it and a current of electricity passed through this wire; this magnetic property exists only as long as the current passes, and stops the instant it is cut off. The catch of the alarm is disengaged by the movement of a bar of iron being drawn to the magnet while the current passes, and forced back again by a spring when it is stopped, thus setting in action the mechanism of the alarm; or in some cases there is a simple contrivance for causing a rapid flow and stoppage of the electricity, so that the bar is alternately attracted by the magnet and released by the spring, and this motion rings the bell as long as it is continued. The bell is always rung to give notice that a message is about to be sent, and at the station where it rings, the bell at the former station is rung in return, to show that they are prepared to receive the message: which is then spelt, letter after letter, by moving the handles into the proper positions, and as it is being sent, the eye is kept on the dials, certain single signs are made and recognised, which will communicate any reply from the station to which the message is being sent, such as “repeat,” or “not understood.” The wires which convey the electricity are made of galvanised iron (iron coated with zinc), and as they must be kept from all communication with the earth by some substance incapable of conducting it, they are therefore stretched between wooden poles (fig. 250), and rest upon sockets or supports of glass or glazed earthenware, which are both substances incapable of conducting the electricity to the earth (fig. 251), and in order that these may be quite dry, an inverted cup of metal, glass, or earthenware is placed over it, or the whole is blown or moulded in one piece. If the support for the wires were not kept from the rain, the wet would form a conducting surface, and allow the electricity to escape into the earth. [Illustration: Fig. 249.—Handles and needles of telegraph.] [Illustration: Fig. 250.—Telegraph wires.] [Illustration: Fig. 251.—Insulator.] The Telegraph Alphabet, in the two-needle instrument, now not generally used in England, is given below.