286
SUBMARINE CABLES—UTILIZATION OF THE ELECTRIC FORCE. [Class X.
bited as means of protecting submarine wires. Brettshows a sort of vertebrated hollow iron chain of consi-derable strength, which is proposed to be built about thewire. But there appear practical difficulties in the appli-cation of these plans. We see some insulated wire, pro-tected by a strong net-work of wire woven over it, whichimparts great strength and elasticity, and will often befound useful. The wires prepared for establishing com-munication between England and France, are coated firstwith gutta-percha, and then twisted together, being fourin number, thickly covered with rope-) urn saturated withtallow and pitch, and finally protected with galvanizediron-wire of the thickness of a quarter of an inch.
A plan worthy of commendation for its simplicity, andfor combining the leading essentials of a submarine wire,has recently appeared. A chain cable of sufficientstrength to resist any strain to which it might be ex-posed, is galvanized; gutta-percha wire is covered withtape, or a similar material, saturated with creosote andoilier matters offensive to animalcule; outside this isanother coating of gutta-percha, and around the wholegalvanized iron wire is wound, like the wire of a harp-string. One or more wires are enclosed in the outercoating of gutta-percha, before applying the galvanizedwire, as may be required. The chain is arranged regu-larly, that is, with the links alternately vertical andhorizontal; and in the four corners or angles presented, islaid one of the wires prepared as above, which is retainedin situ by simple slips of galvanized iron, from which itcan be readily released. The full strength of the chainis thus increased by the addition of the wires, and thecombination is very elastic and manageable.
Insulation is not a little dependent on the state of thecircuit, that is to say, on the relative amount of resistance,opposed to the passage of the force. In short distancesdefective insulation is not much felt, for the resistanceoffered by a few miles of wire, which is a very goodconductor, is far less than that presented by the films ofwater or other bad conducting material near the insu-lators; the relations of these resistances vary with thelength of the wire, and also greatly vary if the resistanceof the wire is increased by badly-made joints. In earlydays the lengths of wire were joined by mere contact,and the pressure of a nut or bolt; and the winders bywhich the wire was tightened formed part of the circuit.This plan was found by no means to satisfy the condi-tions essential to long circuits; and now the joints aremade with scrupulous care, and the lengths of wire aresoldered together from end to eml, the winders not beingallowed to enter the circuit.
Steinheil had discovered, in 1837, that it was not ne-cessary to lead a wire from each pole of the battery, tothe respective sides of the telegraph apparatus at thedistant station, as would be done in all experiments on asmall scale, but that the conducting powers of the earthcould be advantageously substituted for one of the wires.The saving of one out of every two wires, importantthough it is, is not the only advantage derived front thisdiscovery. The earth is found so far to surpass thewires themselves in conducting power, that it addsnothing to the resistance; so that equal effects maybeproduced at double the distance with the same initiativeforce. The resistance therefore for any given distance isone-half, and the tendency towards defective insulationis reduced. The earth acts as the return -wire, to anygiven number of distinct wires, without in the leastaffecting the regularity of the action of any of them.
III. The Utilization of the Electric Force. — Almostevery effect by which the presence of electric force ismade manifest, has been in turn enlisted for the purposeof transmitting our ideas to a distance—not exceptingeven the heating effect of electricity, which have beenemployed by Horn to ignite wire and singe signals onpaper.
1. The spark was employed by Reizen, who pastedstrips of tin-foil on glass, and cut out the letters by di-viding the strips, which intervals were illuminated by thespark. Salva used the spark, but hew converted intolanguage was not known.
2. Recession of similarly electrized bodies occurred to
Lesage, who proposed twenty-four wires, with a pair ofgold leaves at the end of each; one or other of the pairswas to diverge by an electric charge. Triboaillet pro-posed something similar, with only one wire and conven-tional signals. Lomond used a common electrical ma-chine and a pair of pith balls and conventional signals.Ronalds employed pith balls, and two veil-regulatedtime-pieces, which carried round similar discs of signals,each presenting the same signal at a fixed point at thesame time. He deflected his pith balls, and dischargedthe electricity, allowing them to fall when the rightsignal arrived at the given point.
3. The physiological effects of electricity, in otherwords the electric shock, was proposed by Yurssehnan de
; Ileer, and actually tried in 1839. lie had ten wires, and' ten keys or studs, on which the fingers of the hands wereI to be placed; and the shocks felt in the various fingersj constituted the signals. Instead of an alarum to callj attention, the clerk had merely to connect himself up in; the telegraph circuit, when he might safely rely on beingfeelingly reminded when his attention was required.O’Shaughnessy proposed giving shocks from the inducedcurrent, one shock and a group of shocks being the dis-tinctive marks, and each station being provided withtime-keepers, having a disc of signals, a shock to begiven when the index pointed to the letter intended.
4. The decomposing powers of electricity suggestedthemselves to Soemmering. Some twenty or more wiresterminated in gold points, within a vessel of acid water,and according as the circuit was made by one or other of
the wires, a small stream of gas ascended from its termi-nating point, and hence the alphabet, lie also contrivedthat an inverted cone should collect the gas, and wouldthen float and cause a little ball to fall on a detent to| liberate a clock mechanism and a bell. Coxc proposedthe decomposition of water, but gave no plan. Davy im-pregnated cotton with hydriodate of potassa and chlorideof calcium, and having marked it off in checquers, se-cured it on a cylinder that rotated by a clock movement.The current has to be directed through the cotton, andto produce a spot; the checquer on which this spot felldetermined the signal. The clock-work was released byan electro-magnet, actuated by a current in other wires.Bain’s printing telegraph depends on the same principle,applied, however, to the decomposition of more sensitive’ bodies, and reduced to actual practice. He acts upon amixture of sulphuric acid aud prussiate of potash, withwhich he moistens paper bands. The paper is interposedin the circuit, and receives a mark wherever the currentpasses and decomposes the solution. The alphabet con-sists of a combination of short and long marks, producedrespectively by instantaneous currents, and by currentsof short duration. These currents are sometimes sent byhand, by mere making contact; at other times short andlong holes are punched in a dry paper band, and this isdrawn by clock-work between the metal point anucylinder, which closes the circuit, and thus the currentis cut off, when the sound part of the paper intervenes,and passes when the presence of a hole allows the pointto touch the cylinder, and complete the circuit- themoist paper receiving the spots is made to move on at alike rate. Bakewell places his solution in like manner ina paper band; but he writes his messages with varnishupon tin-foil, and places this between the point and cy-linder, aud causes the latter to revolve, and hence thecurrent is intercepted wherever the varnish intervenes;the moistened paper revolves at a like rate, and bothprogress axially, so that a fac-simi!e occurs of what hadbeen written.
5. The galvanometer has been most successfully pressedinto telegraph service, and forms the essential part of heneedle telegraphs which have obtained so marked a repu-tation in England.
Steinheil used one galvanometer coil containing two! needles, which carried ink-cups, and made dots as they| were deflected. Alexander had thirty wires and gal-I vanometers, the needles of which carried screens anddisclosed letters on their being deflected. Schilling, ac-cording to one account, used thirty-six wires, and gal-vanometers, and, according to another account, only one;