passing, takes a position which would be exactly per- system now generally followed by the British and pendicular to the wire if no other magnetic or electro- Irish Magoetic Telegraph Company, the motion maguetic force acted on it; that end or pole of the directly produced by the electro-magnetic force of needle which has the same magnetic quality as the the current causes (by aid of a “relay,” as described north polar regions of the Earth, and which is, below) one or other of two bells to be struek, accordtherefore, properly called its north magnetic pole, ing as the flow of signal current is through the wire, (although generally marked with an S. by British nominally from or towards the sending station. Or instrument makers, ) is driven to the south if the line again, as in the Morse and Bain telegraphs, curof current be from east to west and below the line of rents in only one direction are used, and signals of the needle, or if from west to east and above it. And the requisite variety are produced by making them if the point of support of the needle, and the wire of longer or shorter duration. In the Morse system conveying the current, be held fixed, while the a long ribbou of paper, kept running at a uniform direction of the current is reversed, the needle is rate by wheelwork, is embossed with longer or as much deflected in the opposite direction. The shorter marks by a point pressed against it by amount of this electro-magnetic deflecting force pro- electro-magnetic action as long as the current flows ducible by a current of fixed strength, may be greatly through the line of telegraph. Various forms of inkmultiplied by bending the wire round and round so markers have been devised, and some have come as to convey the current in one direction below the into tolerably extensive use of late. These long needle, and in the opposite direction above it. or short ink-marks are produced with less electro

To carry out this idea, the philosophical instru- magnetic force, but yet with greater and more easily ment maker took advantage of the silk-covered legible distinctness than the embossed long or short wire of the milliners; only using, instead of the iron lines of the original Morse system. wire which had served their purpose, copper wire, The Morse alphabet, as printed on a long narrow as being five or six times as good a conductor of elec- slip of paper by any of the recording instruments, tricity. This silk-covered copper wire came to be is as follows :made into coils, which, with magnetic needles properly supported in their interior, constituted what was A B

D E F G called the galvanometer,--an instrument for measur

H I J K L M ing the strength of galvanic action, that is, simply the strength of a continuous electric current. The silk


P Q R s T covering of the wire played the important part of insulating its several turns from one another, and U V W X Y Z preventing the current from taking any short cut, so as to compel the whole of it to pass through each Any system in which the alphabet is made of two turn of the wire. The needle, balanced on a point, different signals, by positive and negative electric or hung by a fine thread or single silk fibre, re- pulses, is called, after the name of its inventor, mained always with its own length horizontal, and Steinheil. The Steinheil alphabet, most commonly was free to turn round into any horizontal position. used now by practical telegraphers, is letter for letter When no electric current flows, the needle takes a the same as the Morse, but with positive currents, definite direction, either in virtue of terrestrial producing, let us say, a deflection to the right in magnetism, or of the action of steel magnets fixed the receiving instrument, instead of a dot, and an in its neighbourhood. When the current passes equally short negative or left-hand deflection instead through the coil the needle is deflected to a greater of the dash of the Morse alphabet. or less degree, according to the greater or less In the Bain system, as now used on some lines, the strength of the current, and in one direction or the signals, and the ribbon of paper receiving them, are other according to the direction of the current in arranged precisely as in the Morse system. The the wire. Oersted's discovery of this grand law of ribbon of paper is moistened with solution of nut nature early brought in a rich harvest of know- galls, or ferro-cyanide of potassium: and a fixed steel ledge, through the labours of Ampère, Seebeck, wire or thin spring presses it against a metal roller, Cumming, and Faraday; and within twenty years as it runs through the wheelwork. As long as an had an obvious practical application in the Elec- electric current passes from the steel, through the tric Telegraph. In every kind of electric telegraph paper, to the metal cylinder, the steel is eaten away which has been practically successful, the magnetic in very minute quantities, which combine with the virtue possessed by a metal wire during the flow moist chemical preparation on the paper, making of a current of electricity through it, is used in ink or prussian blue, as the case may be, and markthe receiving instrument to exercise force and ing the paper with it. thereby cause motions by which visible effects are But the electric currents used for marking, whether produced. In the simplest forms of telegraph these electro-magnetically or electro-chemically, are not, motions are themselves read directly, as in the in any long line of telegraph, produced by the so-called needle telegraphs still used so much on current through the line. This current produces a our railways; sometimes, again, as in one of the minute, scarcely visible, motion in a magnet, through very early telegraphs, that of Steinheil, and in the the electro-magnetic influence discovered by Oersted. These minute motions serve to make and break the elapse before the piston at the receiving end moves circuit of a special battery, placed to work the through any sensible space. marking instrument at the receiving station, and Not only the general characteristics of the result, kept separate from the battery used in the line but the mathematical law of the whole action, will circuit. A receiving instrument which acts thus is be precisely the same as that of a submarine cable, called a relay, from its being used to give, under if we suppose the motion of the water through the the gaidance of the spent currents from the distant tube to be obstructed by a porous material, as chips station, a fresh relay of power as it were, to carry or minute particles of india-rubber, packed uniforward the message, whether over a farther stage formly into it through its whole length, and of of telegraph line, or merely through the conducting enough of elasticity to press out and fill the tube,

Fire of the marking instrument. The relay, with or to yield to the tube when contracting, during the H one form or another of marking instrument, and very small changes of diameter it experiences in the

forse signals of longs and shorts, or “dots and signalling. Siemens' phenomenon of electric charge dashes," as they are technically called, has hitherto along a line” is here represented by the swellings been used in every great submarine line, until the and contractions of the india-rubber pipe. example of a different mode of receiving messages The copper wire of the submarine cable, adhas been set in the practical working of the Atlantic mitting, but not without resistance, the flow of Cable, which, with the reasons for introducing it, I electricity throngh it, is represented by the hollow sball now briefly explain.

spaces of the tube occupied by the porous material As early as 1849, or little more than ten years filling the tube and resisting, but not absolutely after the practical realisation of the electric tele- preventing, the flow of water through it. The grapà, a principle then new to the scientific world law of this resistance is identical with Ohm's

was pointed out by Dr. Werner Siemens, of Berlin, celebrated law of the resistance of metal wires to | according to which it has since been found that long the electric current. || sabmarine lines lose the sharp quick action charac- The electric charge upon the conductor of the cable li teristic of the electric telegraph as known at that under electric pressure, as we may call it for the

time. Experimental and mathematical investigations moment (or difference of potentials, as the scientific on the subject, which have since been carried out by world learned, long after his death, from George various workers, allow me to explain the comparative Green, the Nottingham miller's son, to call it), is sluggishness of a long submarine telegraph, by an less and less the thicker the gutta-percha is; just as analogy which, though apparently gross and me. an india-rubber pipe will be less and less affected by chanical, is suggestive of the deeper relations and pressure the greater the thickness of its substance. properties of electricity and of speculations as to its One and the same mathematical law applies to the Bature and way of action, learned from Faraday. A two phenomena, even including the relation between water telegraph, which has sometimes been used on thickness and practical rigidity in one of them, and a small scale, consists of a metal pipe filled with smallness of electric charge in the other. water, and communicating at each end with a short If, now, instead of our india-rubber tube, we cylinder stopped by a piston. If at one end (the convert the whole atmosphere of the earth into an sending station) the piston is pressed forward incompressible elastic material, and make a long through a small space into its cylinder, the piston at bore or tunnel through it, in place of the telegraph the other end will be driven outwards through an wire, the circumstance of the ordinary long line of equal space, and, if the former is again driven back, telegraph stretching through the air would be the other piston will return again to where it stood hydraulically represented with like completeness. before. Letters and words may of course be sent The greatness of the solid mass surrounding the and read, by proper combinations of such signals. bore would make the yielding under pressure very If the pipe were perfectly rigid and the water in. much less than in an india-rubber pipe com. compressible, the siguals would be absolutely sharp parable with the dimensions of the gutta-percha in and definite. Each slightest motion of the piston a submarine cable; and the signals would, accordst the one end would produce, at exactly the same ingly, be sharper and quicker. There is, indeed, instant, a precisely equal motion of the piston at the additional gain of sharpness in the air telegraph, in ther end. But if, instead of being of absolutely virtue of a remarkable and most startling discovery ngid material, (which does not exist in nature,) or of made by Faraday, of what he calls “ specific invery rigid material, as iron, the tube consisted of a ductive capacity” of insulating materials. The soft yielding yet elastic material, as india-rubber, it specific inductive capacity of gutta-percha is, acwould, if the piston at one end is pressed forward, cording to measurement made by Mr. F. Jenkin, swell out, under the influence of increased pressure from two to three times that of air. Thus in our at that end, as the water is thrust forward through analogy, the elastic solid taking the place of air the tube; and would shrink to less than its ordinary must be specifically from two to three times as diamcter when water is sucked back as it were by rigid as that which we imagine substituted for drawing back the piston. And thus a considerable the gutta-percha of a submarine cable, to give a time, which may be a few seconds, a few minutes, just comparison of the telegraphic speeds of air and

a few hours, according to circumstances, will submarine lines.


As the galvanic battery is a subtle machine for cisely analogous to an electrometer, or instrument maintaining, by almost innumerable molecular for measuring electric potentials, which may be pumps, driven by chemical energy, a continuous 'substituted, although not advantageously, for the flow of electricity through the circuit of which it galvanometer, or current measurer, as receiving forms a part, and the galvanometer is an instru. instrument. But notwithstanding this, the mathement for measuring the rate of flow of electricity at matical law to which the deviations of the piston any moment; the two pistons do not form a perfect at one end, following gradually after the sudden analogy for the direct use of the battery in sending, impression on the piston at the other end, are suband galvanometer in receiving messages.

ject, is identical with that of the increase of electric But it is interesting to remark that the piston current at the receiving end of the submarine telefor sending signals in the water arrangement is an graph wire, when the galvanic battery is suddenly absolutely perfect scientific analogy for Mr. Varley's applied and kept in action at the other end. application of the condenser described below; and The accompanying sketch represents the simplest the piston to receive and indicate signals is pre possible arrangement of sending and receiving in

[graphic][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed]


struments for any line of electric telegraph, worked deflection indicates a flow of electricity, remaining on the Steinheil system.

in the line from previous signals. The keys (K K'), with the battery, constitute the It was for this purpose that the telegraph mirror sending instrument; the receiving instruments are galvanometer was devised, eight years ago. It indicated by RR'. Each key consists of two metal consists of a very light mirror, with a magnet springs, set to press on a fixed metal bar. Wires cemented to its back, suspended by a single fibre connected with them in the manner indicated in of unspun silk, in the hollow core of a bobbin, the sketch, keep up the metallic connection between wound round with fine silk-covered copper wire. the telegraph line and the earth plate, unless either The adjuncts for its use consist simply of a lamp key is depressed by the finger of the operator. and a proper screen (a scale printed on white paper) When this is done, a positive or a negative current to receive an image of the flame reflected from the is sent into the line, according as one spring or the mirror. The mirror may be slightly concave; and other is depressed. But before beginning to send a if so, it of itself brings the rays to a focus on the message, he puts his own receiving instrument out

Or if the mirror is plane, a convex lens in of the circuit, by a simple movement of a metal front of it, through which the light passes and piece, not shown in the sketch. If the Morse system repasses, produces the same effect. Thus an obis to be used, a single spring key at each end, server sees, as it were, an inverted image of the instead of the double one shown in the sketch, is flame freely traversing the scale, and showing excessufficient.

sively minute deflections of the mirror, by large From the preceding explanation, it will be readily motions, easily followed and read off as signals. understood, that if the moveable magnet of the The mirror is a little more than one-third of an receiving instrument is, as in a relay, limited to a inch in diameter, and weighs one-third of a grain very narrow range in its motion by stops, and if (that is, about half the diameter of a threependythe indication by which the message is sent is piece and about one-sixtieth of its weight). The merely an indication of deflection or no deflection, attached magnet is of about the same weight as the an extremely slow rate of working will be entailed mirror; so that the whole suspended moving mass when the line is submarine and of great length. is less than three-quarters of a grain. A powerful But if, on the other hand, the receiving instrument steel magnet fixed outside the coil causes the susshows truly, by the amount of its deflection, the pended magnet to return with extreme rapidity to actual strength of the current, the sudden effect of its middle or undeflected position, when the dedepressing either key or letting it rise again will flecting force ceases. This instrument may be used be perceptible even although the large varying for either Morse signals or Steinheil signals. Thus

[ocr errors]
[ocr errors]

on the Morse system a dot is indicated by an ex- the line, by which a very considerable increase of cursion in one direction, with rapid return towards speed is obtained. The term “condenser” has long its uodeflected position. A dash is indicated by an been used among electricians, to denote an arrangeexcursion in the same direction, commencing with ment in a moderate compass equivalent to a

Leyden jar of enormous capacity. One coating of this Leyden jar is put in direct communication with the conductor of the cable. The other is joined to the sending key, or the receiving instrument, according as the message is being sent from or received at the condenser station. To attempt to explain the principle of this valuable application, for diminishing the embarrassments experienced in working through a submarine cable, would carry us into details regarding electrical principles beyond the scope of the present paper.

By the very simple arrangements I have now S

described, in the hands of remarkably skilful and N

apt operators, speeds of thirteen or fourteen words a minute were attained through the 1866 cable, within ten days after its completion; indeed, before the Great Eastern had left Heart's Content to recover the lost cable of 1865. It is quite certain that, as soon as a higher speed is demanded for the public service, a higher speed may with great ease be obtained; by means of sending instruments constructed to carry into effect methods which mathematical theory long ago indicated for applying a

battery at one end in such a manner as to produce equal rapidity, but continuing with a diminishing the sharpest and shortest possible effect at the speed for a longer time before the return impulse other. becomes sensible. This was the system employed The question is often put-"What is the velocity in reading the messages which passed through the of electricity?" or, in more familiar language, some1858 cable.

times, “How long does electricity take to go across The Steinheil system, which, all circumstances the Atlantic ?” In truth, we know of no limit to the being the same, admits of a higher speed than the velocity of electricity. In 1834, Professor WheatMorse, in consequence of saving the extra time stone found that the effect of an electric impulse, on consumed by the dashes, has been used bitherto in a circuit of copper wire on which he experimented, working the cables completed in 1866. The positive produced a spark in a distant part of the circuit so current throws the luminous image to the right, quickly, that the influence must have travelled from which it begins quickly to return; but before along the wire at a velocity one and a half times it has returned by one-tenth of the distance to its greater than that of light. This would correspond andeflected or “zero” position, a second positive to a distance of 250,000 nautical miles (or about signal may follow and give it a second impulse a twelve times round our globe) in one second of time. little further to the right, a third may give it imme- At this rate, the first effect of an electric impulse diately after a third impulse to the right. If, after would reach the remote end of the 1850 nautical this, its return to zero is nndisturbed, the reader miles of either Atlantic cable in from seven to eight understands that the letter s (rrr) is meant. thousandths of a second, or something less thau

But if it suddenly begins going much further to a hundredth of a second. In all probability a the left than corresponds to the s, and then settles real electric effect does reach the remote end of the towards zero, the reader understands the letter v cable with some such almost inconceivable rapidity rrrl). Thus, in one case, three positive currents as this. But the mathematical theory proves that, at the sending end, and in the other, three positives after the instant of applying the battery at one end followed by one negative, are read with ease by a of the cable, an interval of from one to two tenths practised eye, even though the luminous image of a second of time elapses before the effect becomes never returns to zero after its first deflection to the sensible to the most delicate instrument at the other right. All that a relay could have indicated in such end. But the explanations which I have given & case, would have been the first contact of the above show that these questions are irrelevant to moving magnet on the stop limiting its excursion. telegraphic signalling through an Atlantic cable ;

The plan which has been actually used in the and therefore, interesting as their subject is, I Atlantic signalling of 1866, differs from that illus- refrain from more than alluding to them in the trated in the preceding sketch by the introduction, present article. due to Mr. Varley, of a "condenser” at one end of



In the spring and early summer of the year now sible, and were repressed. All through Lombardy past,—the year 1866,--the hatred felt by Venetians and Tuscany any young man who pleased might towards the Austrian soldiers who held their city volunteer with Garibaldi; but to volunteer with in thraldom, had reached its culminating poiut. For Garibaldi was not, at first, so easy for young men in years this hatred had been very strong;-how Verona or in Venice. The more complete was this strong can hardly be understood by those who repression, the greater was this difficulty, the never recognised the fact that there had been, so to stronger of course arose the hatred of the Venetians say, no mingling of the conquered and the con- for the Austrian soldiery. I have never heard that querors, no process of assimilation between the the Austrians were cruel in what they did ; but Italian vassals and their German masters. Venice they were determined; and, as long as they had as a city was as purely Italian as though its any intention of holding the province, it was necesbarracks were filled with no Hungarian long-legged sary that they should be so. soldiers, and its cafés crowded with no white- During the past winter there had been living in coated Austrian officers. And the regiments which ice a certain Captain von Vincke, — Hubert held the town, lived as completely after their own von Vincke, -an Austrian officer of artillery who fashion as though they were quartered in Pesth or had spent the last four or five years among the Prague or Vienna, -with this exception, that in fortifications of Verona, and who had come to Venice they were enabled, -and indeed from cir- Venice, originally, on account of ill health. Some cumstances were compelled,--to exercise a palpable military employment had kept him in Venice, ascendancy which belonged to them nowhere else. and he remained there till the outbreak of the war; They were masters, daily visible as such to the eye going backwards and forwards, occasionally, to of everyone who merely walked the narrow ways of Verona, but still having Venice as his headthe city or strolled through the open squares ; and quarters. Now Captain von Vincke had shown so as masters they were as separate as the gaoler is much consideration for the country which he separate from the prisoner. The Austrian officers assisted in holding under subjection as to learn its sat together in the chief theatre,--having the best language, and to study its manners; and had by part of it to themselves. Few among them spoke these means found his way more or less into Italian Italian. None of the common soldiers did so. The society. He was a thorough soldier, good lookVenetians seldom spoke German ; and could hold ing, perhaps eight-and-twenty or thirty years of no intercourse whatever with the Croats, Hun. age, well educated, ambitious, very free from the garians, and Bohemians, of whom the garrison was common vice of thinking that the class of mankind chiefly composed. It could not be otherwise than to which he belonged was the only class in which it that there should be intense hatred in a city so would be worth a man's while to live, but nevertheruled. But the hatred which had been intense for less imbued with a strong feeling that Austria years had reached its boiling point in the May pre- ought to hold her own, that an Austrian army was ceding the outbreak of the war.

indomitable, and that the quadrilateral fortresses, Whatever other nations might desire to do, Italy bound together as they were now bound by at any rate was at this time resolved to fight. It was Austrian strategy, were impregnable. So much not that the King and the Government were so Captain von Vincke thought and believed on the resolved. What was the purpose just then of the part of his country ; but in thinking and believing powers of the state, if any purpose had then been de this, he was still desirous that much should be done finitely formed by them, no one now knows. History to relieve Austrian Italy from the grief of foreigu rule. perhaps may some day tell us. But the nation was That Italy should succeed in repelling Austria from determined to fight. Hitherto all had been done Venice was to him an absurdity. for the Italians, and now the time had come in He had become intimate at the house of a widow which Italians would do something for themselves ! lady, who lived in the Campo San Luca, one Signora The people hated the French aid by which they had Pepé, whose son had first become acquainted with been allowed to live, and burned with a desire to Captain von Vincke at Verona. Carlo Pepé was a prove that they could do something great without young advocate, living and earning his bread at aid. There was an enormous army, and that army Venice, but business had taken him for a time to should be utilised to the enfranchisement of Verona ; and when leaving that city he had asked Venetia and to the great glory of Italy. The king his, Austrian friend to come and see him in his and the ministers appreciated the fact that the mother's house. Both Madame Pepé and her fervour of the people was too strong to be repressed, daughter Nina, Carlo's only sister, had somewhat and were probably guided to such resolutions as found fault with the young advocate's rashness in they did make by that appreciation. The feeling thus seeking the close intimacy of home life with was as strong in Venice as it was in Florence or in one whom, whatever might be his own peculiar Milan; but in Venice only,-or rather in Venetia virtues, they could not but recognise as an enemy of only-all outward signs of such feeling were repres- their country.

« ForrigeFortsett »