281

ESSENTIAL CONDITIONS FOE WORKING ELECTRIC TELEGRAPHS. [Class X.

of, have been, it is presumed, found to be of little practicalvalue.

It would seem that the needle telegraph, giving con-ventional signals, has obtained a firm standing in thiscountry; and with the recent improvements in the gal-vanometer, it has certainly attained a high degree ofperfection. . I

The form of the needle in most general use is that of ja small rhomboid, into which much magnetism can be \imparted, and which vibrates with great steadiness and |rapidity. It, however, has the disadvantage of parting with ;its magnetism much more readily than longer needles, ;and requires to be re-magnetised more frequently. j

When we reflect how very few years have elapsed since jall that was known upon this subject (now the science of jthe age) was confined to a few scientific men, and regard jits subsequent rapid progress, and probable great extern- Ision,* it cannot fail to be both interesting and instructive jto trace briefly its progress, and to examine somewhat in ;detail the essentials of electric telegraphs, with the view ;of seeing how far such are attained in those exhibited. ;It is not the purpose of this report to trace the history 'of inventions, but one of its principal objects is to givemerit wherever it is due, and it is hoped that the follow-ing attempt to classify telegraphs, being the first whichhas been made, is well within its province. In drawingit up we have to acknowledge our very great obligationsto Charles V. Walker, Esq., the Telegraph Engineer tothe South-Eastern Railway Company, for the kind assist-ance which he has freely given.

The idea of utilising the electric form of force, so as tohave the means of rapid intercommunication betweenplaces far apart, is coeval with the discovery of the ex-ceeding velocity with which this force travels throughgood conductors; and hence, as far back as 1782, we havea M. Lesage proposing to deflect twenty-four differentleaves of gold, at the end of twenty-four distinct wires;and in 1787 we have a Mr. Lomond passing signals fromroom to room, by means of a Leyden jar and an electro-scope, experiments useful enough as scientific illustra-tions, or as philosophical toys, but of no practical value.Indeed, so long as we were in possession of no otherform of electric force than that which is obtained in astate of high tension from the joint friction of suitablebodies, there were no hopes, even had man been ready totake up such an invention, of an electric telegraph, pro-perly so called. We find Reizen and Salva at the closeof the last century, and Ronalds at the commencement ofthe present, doing their best to render this wild and way-ward form of electric force subservient to their purposes;and the latter effectually controlling it within certainlimits, and making a telegraph that did some actual work.It was not, however, until Galvani’s discoveries hadopened out a new field of electric research, which was sosuccessfully trodden by Volta, when it was found thatcertain relations existed between heterogeneous bodies,attended always by the production of electric force in anew and much more manageable form;—it was not untilthis discovery of voltaic electricity that the idea of anelectric telegraph became developed with any distinct-ness. We then perceive an advance ; and although theapplications that first occurred were sufficiently clumsyand impracticable, as compared with the knowledge wenow possess, there was enough in Soemmering’s decom-posing points, in Coxe’s decompositions, in Vorsselmande Ileer’s electric shocks, and in other original ideas, toprove that the prospect of ultimate success was stillentertained.

Rut when Oersted had discovered that this new formof force, voltaic electricity, had a constant relation tomagnetism, and that its presence caused the compass-needle to deflect according to unvaried laws; and whenM. Arago had discovered that the same force wouldendow an inert mass of iron with all the wonderful pro- j

* At the time of our writing, the wires are being laid Ifrom Dover to Calais, thus connecting the Continent with 'our system of telegraphic communication ; and arrange- :moats are being made to connect the observatories of jCrccnwieh and Paris .

perties of a magnet, we became possessed of powers,which only required rightly to be handled and controlled,for the solution of the problem; and when, further,Faraday had discovered that the mere motion of conduct-ing bodies in the neighbourhood, or within the sphereof maguetic influence, gave rise to electric force; andPixii first, and Saxton ultimately and effectively hadworked out this discovery, and had produced the magneto-electric machine, there was a choice of means for pro-ducing the actuating force, and we could use at ourpleasure this or that means of generating, what is popu-larly termed the electric current. A third source fromwhence might be obtained the means of actuating thesignalling apparatus, was found in Faraday’s further dis-coveries of the induction of currents in one set of con-ductors, by original currents passing near them in othersets of conductors. It may be supposed that during thislast stage iu the history of electric telegraphs, extendingas it does to this very hour, many unsuccessful attemptswere made, and many discoveries were introduced to thepublic eye, only to be abandoned as futile, and as wantingmany of the essentials to real success;—the name ofthese is almost legion.

The Exhibition contains many inventions which aremost valuable. Perhaps it would be well to considerhere the essential or fundamental points of an electrictelegraph ; they are three in number and are as follows:—

I. The generation of the force.

II. The insulation of the force.

III. The utilization of the force.

We will proceed to speak of them separately.

I. The generation of the force. —In the majority ofelectric telegraphs in actual use, batteries composed ofheterogeneous metals, moistened by a liquid or liquids,are employed for the generation of force. We find thatGrove’s combination of zinc and platinum, excited re-spectively with dilute sulphuric acid and nitric acid;Daniell’s of zinc and copper with dilute sulphuric acid, andsulphate of copper; Smee’s of zinc and platinized silver,with dilute sulphuric acid only; Cooke’s original tele-graph battery of zinc and copper with sand, and dilutesulphuric acid; Walker’s graphite battery, in which thecorrosion from gas retorts is substituted for the copper ofCooke’s; and other forms, have been used by differentinventors. But where a telegraph really requires themore expensive and complex form of battery first de-scribed, there is a priindfacie case against it; for in themaintenance of a large establishment, the cost of suchbattery power would be proportiouably great, and unlesscompensated by some very great advantages on the partof the telegraph would be regarded in no very favourablelight. Siemeu’s telegraph (Zollverein 310a), for instance,is most ingenious and is well constructed; but whetherit possesses advantages over other known plans, that Millcompensate for its requiring to be worked with DaiiielTsbattery, remains to be proved. Again, though as areading telegraph it should not hold this rank, its print-ing powers, as compared with other printing telegraphs,might be greatly in its favour.

The ordinary acid battery has been almost invariablyused in England. It is the least costly in construction,and is maintained at the least expense: it remains activefor a considerable time, but suffers ultimately more duringits resting than during its working periods, on account ofthe combinations that occur between the sulphuric acidand the copper, with the subsequent decompositions.With graphite plates this defect is remedied. ThePrussian telegraph has the peculiar advantage that thebatteries, both at the sending and receiving stations, aresimultaneously in the circuit; and for long distances itavails itself of battery power at intermediate stations.The American telegraphs, in like manner, throw localbatteries into circuit to do the actual work. Thispeculiarity occurs in some of the English patents, butdoes not seem to have been introduced into actual practice.

Perhaps the most curious proposition for the conversionof battery power into language is that of M. Botto, whosesignals depend on the number of pairs of battery platesemployed to deflect the distant needle, and are interpreted