JELAY IV, lOO:i.j 



■r\. iN KJ VV l-i IZj JL^ \-7 JZi 



THE ELECTRIC TELEGRAPH. 



By W. Lyxd. 

 CIRCUITS AND GALVAXOMETERS. 



IN a prcWous article I explained that when the wires attached to 

 the metallic plates of a simple voltaic cell are joined together, 

 chemical action bejiins, and a current of electricity is said to flow 

 from tlio zinc throuy;h the liquid to the copper, through the wii-e, 

 and back to the zinc plate. Without a complete circuit, telcgraphy 

 18 impossible. For instance, suppose that a wire is connected to 

 the terminals of a batter)-, and carried on poles to it.s destination — 

 Bay from London to Birmingham — and the extremity of the wire 

 attached to the terminals of an instrument at the latter place, no 

 current would be received at Birmingham. If we lay on a water- 

 pipe from a reservoir to a private house, water will flow through 

 the pipe, and it can be drawn off by means of a tap, when rctiuired. 

 Compare the voltaic battery with the reservoir, tho conducting 

 ^rire with tho pipe, and tho differeuco will be clearly under- 

 stood. From the reservoir, one pipe is suflicient to enable tho 

 water to flow, but the voltaic battery must have a wire 

 or conductor in connection with its positive pole carried to its 

 destination tlirough the instrument and back again to the negative 

 pole ; the current must make a complete circuit, no matter how 

 great the distance may be between the two poles of tho battery. 

 In actual practice, the return wire is dispensed with, and tho earth 

 performs the functions of a second wire, and completes the circuit 

 in a very remarkable manner. To make what is called the earth 

 circuit iierfectly clear, take a voltaic cell, and instead of bringing 

 the wires in contact, connect them with two plates of metal buried 

 in the earth, or, for convenience sake, join the wires to the gas or 

 water-pipes ; the current williflow as before, and in exactly the same 

 direction. The earth actually plays the part of a metallic wire, and 

 the electric curren^ flows from plate to plate, no matter how great 

 tho distance may be. The essential jiarts of a telegi-aph circuit are 

 the battery, or generator of the current, the conducting-wirc. tlio 

 earth, and the instrument for recording signals. The circuit is 

 ■open when there is a break in the wire, and closed when it is con- 

 tinuous and the current is flowing. 



The time a current takes to flow from pole to pole in a circuit is 

 imperceptible to the senses. A telegram can be sent from London 

 to Glasgow or Paris, as quickly as from St. Martin's-le-Grand to 

 Shepherd's Bush. During the recent repairs of the telegraph cable 

 near Bombay, the steamei-s Chiltem and Great Nortliern were about 

 half-a-mile apart, the former having hold of a shore-end cable, 

 and so was in telegraphic communication with Bombay, the latter 

 having hold of a sea-end, aiid so was in telegraphic communication 

 with Aden. The Chiltern desired the Great Northern to splice on 

 to the cable-end held by the latter, and pay out three-quarters of a 

 mile of cable, and this was communicated by wire from the test room 

 •of the Chifferii, passing through all the coils of cable in her hold, and 

 on to Bombay, whence it was sent on to Aden, and back from Aden 

 to the Great Northern ! Thus, as a speedij means of sending a message 

 half-a-mUe, it was forwarded by a route between three and four 

 thousand miles long ! The following morning, when the two vessels 

 were within a quarter-of-a-mile of each other, communications passed 

 between them constantly in the same way. Of all tho miracles of 

 modern science, truly this annihilation of distance is the most won- 

 derful ! The student will now understand how the electric current 

 is generated, and conducted to its destination. He will, however, 

 naturally desire to know how the electricity which flows through 

 the circuit is made to record signals — in short, how intelligible 

 communication is established between two distant places. All 

 telegraph signals depend on the power of the telegraphist, who, 

 to make them transmit, controls and modifies the current at will. 

 Let us imagine a battery of scvtral cells in the oflice of the editor 

 of this journal in Great Queen-street, and suppose that we connect 

 a wire to tho positive pole, and carry it on posts to the Observatory 

 at Kew, where the wire must be attached to a plate buried in the 

 earth or connected with the gas-pipe. Join up the negative pole of 

 the battery with a buried plate or gas-pipe, and the circuit will 

 be complete. Cut the wire at any point between London and 

 Kew, and the circuit will be broken — no electricity will flow 

 through it. The current can be instantly reestablished by 

 bringing the cut ends together. Xow, if we had some kind 

 of apparatus that would make the currents visible, we could 

 easily arrange a code of signals to rejiresent the letters 

 of the alphabet. There are now many ways of recording 

 signals. Some of the instruments used are very complicated, and 

 depend to a great extent upon ingenious mechanical contrivances. 

 The simplest form of instrument is called a galvanometer, a modifi- 

 cation of which is known as the receiving portion of the needle 

 telcgrapk- To understand the principle of the galvanometer, the 

 relations between electricity and magnetism must be studied. A 

 very simple experiment will suffice to prove that electricity is 



influenced by magnetism, and vice versa. A copper wire suspended 

 horizonally over a movable magnetic noedlo will, when connected 

 with tho poles of a voltaic battery, cause the needle to place itself 

 at right angles to the wire. If the ciurcnt passes above the needle, 

 and goes from south to north, tho north pole of the magnet ditlects 

 towards the west. If the current passes below the needle, also 

 from south to north, tho north \>o\e will deflect towards 

 tho east. If tho current pas.ses above tho needle, but from 

 north to south, tho north jjolo is deflected towards tho east. 

 If the current goes from north to south below the noodle, 

 tho deflection is towards the west. To enable the student 

 to remember these movements, Ampere suggested the following 

 rule : — If we imagine a man swimming in tht>: wire, with the 

 current, with his face turned towards tho needle, tho north pole of 

 tho needle will bodeflccted towards his left hand. According to Preece, 

 " the motion of the needle is produced by tho mutual action of 

 currents and magnets. Electricity and magnetism arc so intimately 

 related to each other, that by many they are thought to be only 

 different phases of the same agency. Thus tho motion of a magnet 

 always produces electricity ; tho transference of electricity always 

 produces magnetism. The neighbourhood of a current is, in virtue 

 of ,thi3 fact, a modnetic _fiel(l, a term introduced by Faraday to 

 denote the entire space through which a magnet diffuses its in- 

 fluence — and a magnet or piece of soft iron placed there is influenced 

 by the magnetism of that field." To increase the intensity of 

 tho cuirent, the wire is wound several times round tho magnetic 

 needle, each coil being still parallel. Each successive coil pro- 

 duces a .oeparate effect ujjon tho needle, so tliat if there are 

 a great number of coils of wire passed carefully before and 

 behind tho magnet, the deflecting force will, bo multiplied in 

 proportion to the number of coils, and the mqst feeble current 

 can be made to affect tho needle. The fine wire, used for this pur- 

 pose is covered with cotton, silk, or some substance which is a non- 

 conductor of electricity. If the coils of wire were not insulated, 

 they would allow the current to pass from coil to coil, instead of 

 following tho continuous thread of -wire. The wire is coiled round 

 a frame, in the centre of which is suspended tho magnetic needle ; 

 upon the same axis is fixed a steel indicator, which points to a scale, 

 and this measiu'es the strength of the current sent through tho 

 wire. Tho galvanometer is included in the circujt, and when con- 

 tact is made, the indicator, which hangs in a vertical ijosition when 

 at rest, deflects in proportion to the intensity of the, current. The 

 single needle instrument, which is only a modification of the gal- 

 vanometei', will be explained in a subsequent article. 



Replv to Query. — [3-19] — Quotation, p. 502 : — 

 " Little things 

 On little wings 

 Beai' little souls to heaven," 

 Are lines taken from a poem written by Father Faber.' 



Tlbekcle and its Cure. — The consequences that wiU be wit- 

 nessed as flowing from the studies conducted by Koch in connection 

 with tuberculosis are impossible to foreshadow in any completeness, 

 but we can, even at this early stage, perceive something of the 

 widespread benefit that may ensue from them and their publication. 

 Kot least important of these must be considered the bearing which 

 antiseptic treatment has been shown to have on the productive 

 cause of the disease ; the inference that is irresistible from a careful 

 survey of the facts demonstrated by Koch's researches, indeed, is 

 to the effect that we may very possibly find a future remedy for 

 incipient, and even for pronounced, jihthisis in the submission of 

 the infected individual to active antiseptic measures. In this 

 connection, an instructive and important communication has 

 been male to tho Times by Mr. R. R. lladdison, who states 

 that, having proceeded to Jtadeira in the hope of simply pro- 

 longing life somewhat, but with absolutely no prospect of recovery 

 from the consumptive condition, he resorted to the uso of carbolic 

 acid as a jn-otection against mosquitoes. Tho vapour of the acid 

 was necessarily inhaled by him, and to its beneficial effect on his 

 lungs he ascribes an improvement in his state. lie continued the 

 use of the acid, and returned to England recoytred, with the further 

 conseriucnce that he has remained well ever since. If, as seems 

 quite justifiable, we may attribute this cure to the destructive effect 

 of the germicide acid on the bacilli of tubercle, there opens up a very 

 grateful prospect of possible relief in innumerablo cases of lung 

 disease; and at any rate it offers strong inducements to resort to 

 treatment at once easy and possessing such promise of successful 

 results. — Medical Press. |__ 



SPECIAL NOTICE TO OUR READERS. 

 Fourpenee each will be paid by the Publishers for copies of 

 Nos. 2 and 3. Apply or address, Wyman & Sons, 73, Great Queen- 

 street, London, W.C. 



