The transmission of signals by semaphore systems was necessarily slow (about one signal per minute), inasmuch as each signal was veri fied by the receiving station before another was transmitted. The time taken in transmit ting a signal or letter from Paris to Toulon was, however, comparatively speedy, namely, 10 to 12 minutes.
Semaphore signaling is still usefully em ployed in some countries for communicating from ship to shore, between coast-guard sta tions, at rifle ranges, etc. One plan of this kind consists in the use of two small flags, one held in each hand. The flags are about 18 inches square, the staff is about three feet in length. The letters of the alphabet are repre sented by the positions in which the flags or the arms are held. With the aid of a telescope, signals may be transmitted by this method to a distance of three miles in fair weather. Messages may also be read by the use of the arms alone, employing the same alphabet, in which case this is termed the human sema phore.
Electric Telegraph Systems.—Although up to 1852 a number of visual systems of teleg raphy, such as the semaphore system, were, as stated, in quite extensive use, electricity had been utilized experimentally long prior to that date for purposes of telegraphy but its growth in this direction was slow and the scepticism with which its commercial utility was at first rerded is evidenced by the ex tensive establishment of semaphore stations, just mentioned, long after the possibility of electric telegraphy, had been more or less • clearly indicated. • In 1774, Lesage of Geneva constructed an electric telegraph system •which employed in its operation 24 line wires, one for each letter of the alphabet. At the•terminal of each wire pith balls were suitably susptnded, and,•talcing advantage of the well-known repellant effect that follows the simiktr electrifies/diem of such light substances, Lesage, by the use of frit-, tiotial electricity applied to the wires trans mitted intelligible signals over them. In 1815 Francis Ronalds of England improved on this arrangetnent A revolving dial, operated by• clock-work, was employed at each end of a wire. The dials rotated synchronously. •A notch was cut in each dial, behind which the letters of the alphabet were placed in, a circle,. se that as the cfial reitelved one letter at a, time was seen through the ncetch. Pith balls
were electrically connected at each end of the, wire. At a given signal the dials were set in rotation and as the notch arrived at a desired' letter the pith balls were actuated electrically. , The letter was noted and in that way tnessages were transmitted. In 1774 Volta had discov- • ered that electricity could be generated by means of the '
Needle TelograPh Systensg.--Aralitig- pf Oersted's discovery that a pivoted magnetic need* is deflected from its normal positidn, parallel to a wire, when an electric curred passer in that wire needle telegraph s steins came into rmicrenee and were- • -eft ployed in Europe at one time .and are yet in use them. For this purpose a magnetic needle, is pivoted in the centre of a coil of wire, and a pointer suitably attathed to the nedle, swings in front of a dial. The needle and with it the pointer can be deflected to the rig,ht or left by changing the direction of current through the ,coiL Certain deflections of •the needle to the right or left, or ,cotabinations of deflections to the right and left represeat the , letters of the alphabet, and these deflections are produced by sending over the wire current pulsations in positive or negetive direction, or alterations of both, as required by the letter to be transmitted. For instance, if the Moure alphabet were used, a motion to the right would represent a dot; one to the left a dash. The alterations of polarity are transmitted by a adrop-handlep or a "tapper.9 The tapper is similar to the double-sending key used in sub marine telegraphy. (See Fig. 15). A needle sys tem employing two needles has also be,en .used. This required two wire.s, but gives a higher rate of speed — about 15 to 20 words per minute. The operator reads incoming signals by observ ing the movements of the needle or needles.