Class X.]

NEEDLES AND OTHER INSTRUMENTS USED FOR SIGNALS, &c.

287

and lie had a plan for checking the oscillations of theneedle. Davy showed, in 183G, what was apparentlya needle telegraph, somewhat similar to Alexander’s.Gauss and Weber had a single needle telegraph, the de-flections to be observed with a spy-glass. Fechuer sug-gested twenty-foul* galvauometers and their respectivewires. Lotto’s plan of one galvanometer, whose deflec-tions w T ere to be neutralized by an adverse current, hasbeen already named. Mason suggested a single galvano-meter. Galton has published a description of a verycomplex apparatus, the electric parts of which are threegalvanometers, whose office is merely to present needlesas mechanical obstacles in certain spots among a train ofmachinery. Cooke and Wheatstone at first used fiveneedles on a lozenge-shaped dial, two of which werealways used for a signal; and the letter was found wherethe points produced met. The needle instrument nowin common use, and in which one or more deflections ofeither or both needles in one or other direction, gives allthe combinations necessary for conducting rapid corre-spondence. The details of these instruments have beenmuch improved, and there is little wanting to make themperfect. There is also a single needle instrument, whichgives all necessary signals, but not so rapidly. The suc-cess of the needle telegraph has led to many modifica-tions of the galvanometer. Brett and Little coil thewire on a circular bobbin, and make a crescent-shapedneedle, the poles of which are properly presented to thecoil; instead of reading from the prime motion of theneedle itself they read from indices, which are moved bya tap from the needle. Highton's galvanometer needle ishorse-shoe shaped, and the coil also circular and dulyadjusted to the needle. He reads from an index carriedon the same axis with the needle. He has also threeneedles, each carrying a screen, transpierced in suchsort that by a combination of motions twenty-six dif-ferent letters can be exhibited to the eye. Little hassuspended an ordinary needle to the pole of the magnet,and withinside a tube of alcohol. The galvanometer coilsare fiat bobbins.

The electro-magnet has been used by Bain, Bakewell,Barlow, Breguet, Brett, Cooke, Davy, Dering, Dujardin,Gamier, Hatcher, Henley, Ilighton, House, Lodefink,Morse , Nott and Gamble, Palmicri, Siemens, Smith,Vail, Wheatstone, Wishaw , and others. In the hands ofsome of these inventors it has been made to give directsignals; for instance, in Henley’s instrument the arma-ture carries the index needle, and the combination of thedeflections of two needles gives the alphabet. In Morse ’sthe armature carries a point which impresses permanentmarks on paper; it is also connected with wheel-workfor moving the paper onward. In Dering’s the mag-netized armature carries the index needle. In Dujardin’sthe armature carries a point that dips in ink and makesdots. Siemen’s prints by the direct blow of a hammercarried by the armature, although his type is brought inby a secondary action. In the hands of others it com-municates motion to the index, as in Breguet’s sema-phore instrument, where the armature acts upon scape-wheels, and gives to the indices the eight positions ofthe ordinary semaphore. Jn Nott and Gamble’s thearmatures carry claws that draw a wheel round, andwith it the index, till it points to the given letter. InSiemens’, the armature acts in a similar manner. Wealso find a third class of instruments in which the motionof the armature releases a detent, and liberates a clock-train, the motion of which produces the signals. Cookeand Wheatstone’s alarum is sounded in this way, thehammer in some cases representing the pendulum bob,and in others, being carried on the produced radius ofone of the wheels. Brett prints by the successive actionof a detent liberating clock-work. It would be no easytask to follow the several inventors through the essentialdetails of their apparatus; nor would it be very prac-ticable to prepare a complete list of all that has beeneither conceived, contrived, or constructed, togetherwith all that has been tried, and proved successful orotherwise in this wide field of research. It may well besupposed that many of the plans to which we have re-ferred, have existed only in imagination—that many are

absolutely useless—that many others are too complex foractual service—that some perform badly and with un-certainty that which others accomplish rapidly and suc-cessfully.

The French Government required signals to resemblethose of the old semaphores, and they have extensivecodes. We have in England preferred conventional sig-nals, thinking it better to train young men to read a newalphabet than to have an index going through the com-paratively slow operation of pointing to every letter. InPrussia the latter plan is preferred. There has been also achoice between reading and print ing instruments: in Ame-rica the latter have prevailed; in England the former.But whatever be the actual sign by which we obtain pos-session of the ideas transmitted to us, it would seemthat the instruments that have obtained a standing, are,almost without exception, those whose action is direct,and are not the result of any extraneous mechanism.

We will now proceed to a careful description of theseveral telegraphs.

The Klkctric Telegraph Company (pp. 477*, 47S*)exhibit many telegraphs.

I. Patent 184G, a rhomboidal needle. The galvano-meter coil is in two halves, mounted on arms, which aremade to open for the reception of the needle, and toclose again. On the same axis is mounted the imlex-needle that is presented to the eye on the face of thetelegraph, and which oscillates between ivory studs.The studs are now made moveable, as first proposed byCharles V. Walker, Esq., Telegraph Engineer to theSouth-Eastern Railway Company, for the needles towork between, so as to keep the neutral position, byadjustment, half way between them during periods ofmagnetic disturbance.

II. Wheatstone. —The instrument marked “ Mag-netic-electric Induction Machine,” consists of a stronghorse-shoe magnet, of eight plates, and 10 inches fromeither pole to the centre, fixed on a board; over it isplaced a handle, which raises and depresses two coilsof soft iron core and armature. On breaking contact, bydepressing the handle a current of momentary durationpasses out from one coil along the wire to the other inone direction. This gives a single impulse only, andalways one way; and is used to excite an electro-magnet,and ring a bell.

III. Hatcher’s magneto-electric induction machineto send currents ad libitum, in either direction. This iseffected by the same application of coils to a horse-shoemagnet and breaking contact; but there are two handles,and according as one or other is used to break the con-tact, cross communication takes place. “ Hatcher’s Cur-rent Director” affords a mode of making and breakingcontact by cross communication, as an appendix to anytelegraph. Jn this machine the horse-shoe is 12 inchesin length, and consists of eight plates.

IV. Wheatstone ’s patent rotating induction machine,for working the disc telegraph (1841). A dial wheelwith spokes and letters. Each letter as it is 'wanted isbrought to a given point. The wheels work a pinion,which causes a pair of coils and armature to revolve overthe poles of a great horse-shoe magnet. Every letterbrought past the given point makes half a revolution ofthe coils and breaks, and renews the circuit oppositeways. The currents thus established and sent off to adistance, pass through coils and actuate local electro-magnets, which alternately attract to and fro an ironplate, and thus alternately release and lock a detent. Aclock, driven by a spring or weight, being thus allowedto act at intervals, drives round a dial-band, click byclick, at tlie other station, and thus imitates the motionof the original dial-wheels. This clock, however, re-quires to be wound up, and it does not seem to providefor any notice being given when it is down.

V. Barlow’s patent, 184S. A printing telegraph,consisting of a circle of letters brought round in succes-sion till the letter wanted comes to a given place; contactis broken as each letter passes, and the current is re-versed; the currents so established act (at the otherstation) as four coil magnets, See., between which a softiron bar is thereby caused to oscillate, and to lock and