Class X.] INSULATION OF TELEGRAPHIC WIRES—COMPOUND NEEDLES, &e.
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of insulation of telegraphic wires. The great practicaldifficulty in telegraphic operations is to overcome thedefective insulation consequent on the dampness of theclimate. To speak first of the wires suspended in theopen air, Mr. \Valker has substituted for the old form ofcone, to which there were many objections in practice, alarge open-mouthed cone, or rather hollow double cone,so constructed that the wire and the cone should be incontact at the smallest possible surfaces; also that, as theplace of contact is as far as possible witliinside the cone,it should be as inaccessible as possible to wet; also fromits shape, that any wet attaining to the cone would, bymere gravity, run away from the place of contact; alsothat the part of the cone, where in contact with the wire,should be at the furthest distance from the timber of thepole sustaining all. After suspending the wires, Mr.Walker has the cone covered in with a roof, having sidesand ends.
The wires from Red Hill to Shalford, a distance of 19miles ; from Ash to Reading, 19 miles ; from Ashford toSt. Leonards, 23 miles; and from Tunbridge Wells toRobertsbridge, 15 miles, are all suspended in this way.These lines are remarkable for their perfect insulationand good working order. It was feared that the birdswould build nests in the roofs, but such, as yet, has notbeen the case. This plan involves no additional expense.
I. In regard to Tunnel HTres.—The deposit of dampand dirt on the suspension apparatus of Mr. Walker’stunnel wires, on the South-Eastern Railway Company’slines, as first erected for him, caused so great a loss anddistribution of the voltaic force, that without some im-provement a total obstruction of telegraph business wouldhave ensued, and messages to Dover, instead of passingdirect, must have been transmitted through an inter-mediate station.
About the time that Mr. Siemens, of Berlin, was con-triving wire covered with gutta percha, it occurred toMr. Walker to direct Mr. Foster’s attention to thatsubstance, and to request that a specimen should beprepared for him. The result was, that Mr. Foster obtaineda patent, of which the Telegraph Company have themonopoly. It was first used in Mr. Walker’s tunnels,where, instead of the old mode of suspending, it is nowlaid in a grooved board covered in. The grooves areploughed by machinery; the board is prepared withmineral varnish, aud is secured close to the tunnel walls,remaining, when once nailed on, in good working order,and in a perfect state of insulation. This grooved board,simple as it is, will doubtless prove a valuable invention,and those who have felt the charge of badly insulatedwires will appreciate the improvement. Compared withsuspended wires, it is important to the safety of trainsand passengers. The old wires have many times beenentangled with trains, not only being torn down, butputting the lives of all exposed in jeopardy. Severalnarrow escapes of this kind have occurred. The lasttunnel on the South-Eastern Company’s lines, that be-tween Iligham and Rochester , is now being fitted up withgrooved boards; and this hoard is used on all sustainingwalls, of which there are many on the North Kent line ;in leading in to stations sometimes down the wall, atother times under the floor. Being prepared by ma-chinery, it is not at all costly.
II. (Jompound Needle. —The first telegraphs made werefurnished with long coils and needles. Mr. Holmesintroduced the needle, now in general use, in the form ofa rhomboid, with a much smaller coil of silk-coveredwire. By means of this improvement, legible signals areobtained through longer distances, and can be conveyedvery rapidly and distinctly. But the great inconveniencewith this needle is the readiness, as we have alreadymentioned, with which it parts with its magnetism, losingit by little and little during the ordinary use of the instru-ment, at times suddenly and often totally when lightningdischarges occur near the wires. With a view of ob-viating these inconveniences, Mr. Walker has substitutedfor it, in the same small coils, an ivory disc, havingseveral short rectilinear needles placed side by side uponit, and at small distances apart. These needles possessall the good qualities of the rliomboidal; but they give
a more dead beat, and are less disposed to part with mag-netism. They have not yet been tried in exienso; butMr. Walker has tested them for long periods at im-portant stations, and is now about to use them extensivelyon account of the serious interruption that lias occurredsimultaneously in all parts of the country from loss ofmagnetism. During this summer it was not of unfre-quent occurrence to have two or three magnetizers, tra-velling as rapidly as possible from station to station, toremagnetize; and sometimes before their day’s work hasended, demagnetization had again occurred at somestations.
III. Jlell Transferers. —This application is not gene-rally employed, ami is constructed specially for the chiefoffice at Tonbridge . It is for placing the bell, when onepart of the line is in use between London and Dover, onthe part or side not in use, so that its ring may lie heard,aud thereby notice given that the line "is wanted, liythis arrangement the necessity of cutting short thecommunication, or rendering it as brief as possible, isindicated.
The bell and needle being on the same wire, this wireis cut at Tonbridge in the three proper places, viz.,between London and the bell, between the bell and theneedle, and between the needle and Dover, making sixends. These ends are made to terminate in springs,winch rest on brass plates, inlaid in a wooden cylinder.In one position of the cylinder the springs are connectedin the order, London , bell, needle, Dover; so that whentalking to Dover, having the line cut off between theneedle and the bell, by connecting the wire here with theearth, the bell can lie heard to ring, should London senda curreut along the wire. In the other positions of thecylinder the springs are connected in the order, London ,needle, bell, Dover; and similar advantages are expe-rienced in respect to Dover. This plan works well. Onthe same principle of combination Mr. Walker constructsall his turn-plates, of which he has many varieties : thefollowing is one :—
IV. liranch duuble. Turn-plate. —This apparatus is usedat junction-stations for putting branch lines of telegraphin communication with either end of a main line, ft isconstructed by intercepting the branch wires before theyterminate in the earth, and by cutting the main wires andproviding springs at the intersections. The springs areso arranged that, in the normal position of the drum orcylinder, the terminal stations of the main line are opento each other, and the branch line terminates at thejunction-station. In another position of the drum, theLondon terminus of the line is connected with the branchline, and the wires from Dover end at the junction-station.In a third position of the drum, the Dover terminus is inconnection with the liranch line, and the wires fromLondon end in the junction-station. This is in daily useat the stations on the line, and acts well.
V. Lightning Conductor. —This consists of a smallhollow metal cylinder connected with the earth, its pur-pose being to conduct away the discharge. The line-wire, in its passage from the railway to the telegraph,passes within this cylinder ; traversing which it is firstpresented to the inner surface in the condition of a thickwire, furnished with spurs, whose points are in the closestpossible proximity to the cylinder, without being in actualcontact; it is then continued on and presented as a shortcoil of very fine wire,—finer, in fact, than that of theinstrument coils, wound on a bobbin,—tiie outer convo-lution of the coil being very close to the cylinder. Thusa better means of escape “is presented to' the lightningthan is to lie found in any part of the instrument, con-sequently it always escapes by this conductor eitherthrough the points or by burning the fine wire. As vetno instance lias occurred in which these conductors havefailed to act, and to preserve the instrument; whileinstruments in the same office, not thus protected, haveon several occasions been damaged.
VI. Graphite Batter;/. —The ordinary telegraph batteryconsists of plates of amalgamated zinc and clean copper,in cells filled with pure sand, saturated with dilutedsulphuric acid. The majority of telegraph batteries arein actual use during a small portion only of each day,
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