Discoveries and Inventions of the Nineteenth Century

by one in the lower line a little to the right, represented A; one in the lower line, followed by another in the upper line, indicated N; and so on. By the dot printing it is said that Wheatstone would signal 700 letters per minute. There were, however, objections to the new code of signals: all the world had agreed to use the Morse alphabet, and it was perhaps less liable to incorrect reading; and for other reasons this more rapid signalling was unsuitable for submarine lines. The apparatus has therefore been modified to suit the dot and dash system of signals, and great improvements have been effected by Sir Charles on the original instruments, with a view of increasing the rapidity of transmission as much as possible. The paper as punched for the Morse signals shows a row of equidistant holes in the middle, by which the paper is guided uniformly forward, and in the outer rows are holes arranged in pairs, either exactly opposite to each other or obliquely—the former produce dots at the receiving station, the latter dashes. From 60 to 100 words can thus be sent and printed in one minute, and the automatic transmitting system can be applied to the needle, or any other form of telegraph. After a clerk has for some time been habituated to working with the Morse instrument, he is able to read the message from the different sounds made by the armature, as dashes or dots are respectively marked, and he usually listens to the message, and transcribes it at once into ordinary language by the ear alone. This observation soon led to the adoption of sound alone as the means of signalling, and an instrument on this plan has already been referred to. Among the more remarkable forms of recording telegraphs, that of Hughes may be mentioned, in which the message is printed at the receiving station in distinct Roman characters; and as only a single instantaneous current is required to be sent for each letter, the speed with which a message can be dispatched is about three times as great as with the Morse instrument. These advantages are, however, obtained only at the cost of great delicacy and complexity in the apparatus, so that it is unfit for ordinary use, although it is much employed on important lines, where competent operators and skilled mechanics and electricians are at hand to keep it duly regulated. This machine is too complicated for a full description in these pages, although it is the best form of type-printing telegraph, and possesses a special feature in the fact that the printing is done whilst the wheel carrying the types is in rapid rotation. The reader will find full and untechnical descriptions of this and of all the more important forms of telegraphic apparatus in Mr. R. Sabine’s useful “History and Progress of the Electric Telegraph,” or in Lardner’s work as edited by Sir Charles Bright. Fig. 289.—The Step-by-step Movement. Fig. 290.—Froment’s Dials. From the numerous forms of dial telegraphs we select two for description. All these instruments are characterized by what is called the “step-by-step” movement, and differ in their mechanical details, and in the nature of the apparatus for producing the currents, some being driven by electro-magnets and others by galvanic batteries. Their principle may be easily explained. Suppose that a ratchet-wheel, having twenty-six teeth, is mounted on an axis carrying a hand over a dial having the letters of the alphabet inscribed upon it. A simple arrangement in connection with an electro-magnet, somewhat like the escapement of a clock, will serve to advance the wheel by one tooth each time a current passes. The diagram, Fig. 289, will at once make this principle clear. E is the electro-magnet, F the armature, separated by the spring, S, from the magnet, except when 567the current passes, when the catch, C, draws down the tooth in which it is engaged, so that a tooth passes under the point at D; and when the current ceases, the spring, S, brings up the catch to engage the succeeding tooth, and thus the hand moves step by step in the direction of the arrow, advancing each time the electric circuit is closed by one twenty-sixth of a revolution. In Fig. 290 is represented lecture-table models of a step-by-step indicating and transmitting instrument, as constructed by M. Froment, of Paris. These instruments are supposed to be at the extremities of a long line of wire. The left-hand figure is the manipulator, or sending instrument, in which the operator has merely to quickly turn round the index in the direction of the hands of a watch, by means of the knob, P, until it points to the desired letter, pause at the letter for an instant, and then quickly continue the movement until his index points to the cross at the top of the dial, where he pauses if the word is spelt out, and, if not, continues the rotation until he arrives at the next letter, and so on. All these movements and pauses the hand on the indicator will accurately repeat, and the reason of this may be seen by observing that the battery contacts are made by the projections on the metallic wheel, R, which turn 568with the index. The spring, N, is always in contact with the wheel, but the spring, M, has such a shape that contact is alternately made and broken as the projections and spaces pass it. It is obvious that the needle of the indicator will therefore advance over the same letters as the index of the communicator. Fig. 291.—Wheatstone’s Universal Dial Telegraph. A very elegant dial instrument has been invented by Sir Charles Wheatstone, in which magneto-electric currents are made use of. In Fig. 291 communicator and indicator are represented mounted in one case, or small box. The larger dial is the communicator, and its circumference is divided into thirty equal spaces, in which are the twenty-six letters of the alphabet, three punctuation marks, and a +. In an inner circle are two series of numerals and other signs. About the circumference of the dial are thirty small buttons or projecting keys, conveniently arranged, so as to be readily depressed by the touch of a finger. Inside of the box a strong permanent horse-shoe magnet is fixed, and near its poles a pair of armatures of soft iron cores with insulated wire coils revolve when the handle, A, is turned, as in the machines described in the last article. In this manner a series of waves or short currents of electricity are produced in the conductors when the circuit is complete, and the currents are alternately in opposite directions, so that fifteen revolutions of the coils will produce fifteen currents in one direction and fifteen in the other. A pinion on the same spindle as the coils works with a wheel on the axis carrying the pointer on the dial, so that the pointer makes a complete revolution as often as the handle, A, makes fifteen turns. Each of the thirty currents will pass through the indicator, I, and through the line to the distant station, where they will, by a step-by-step movement, advance the needle of the indicator. So that the hand of the dial and the needle of the indicator at the sending station, and that of the indicator at the distant station, will 569all simultaneously be pointing to the same letter on their respective dials; and they would continue to move round these, ever pointing to the same letter, so long as the handle, A, is turned. How, then, is the sender to cause the needle of his correspondent’s instrument to pause at any desired letter? Not by stopping the revolution of the handle, A, for that could not be done so as to send just the right number of currents, inasmuch as the rotating armatures could not be instantly stopped. The mode of causing the indicators to pause at any required letter is as simple as it is ingenious. It has been already mentioned that the step-by-step movement takes place at every current which passes through the line, including the two indicators, and that thirty such currents pass at each revolution of the pointer of the communicator. But when these currents no longer flow, the indicators, of course, stop; and the stoppage of the movements is reconciled with the continuous production of the currents by having a series of little levers, each connected with one of the buttons, and so arranged that when one of these has been pushed down, the lever stops the revolution when it has come round of an arm on the same central axis as the pointer, and riding loosely on a hollow spindle, which bears the toothed wheel, driven by the pinion already spoken of. The projecting arm is provided with a spring, which falls between the teeth of the wheel, so that the arm is with certainty carried round with the wheel. But where a button has been pushed down, its lever catches the arm, lifting its spring away from the teeth of the wheel. So long as the key remains down, the arrested arm makes a short metallic circuit by its contact, and no currents pass into the line, for they take the shortest path. The key is raised only when another is depressed, and then the arm and the pointer immediately resume their revolution until they again become stationary at the letter corresponding with the key which has been pushed down. Suppose the key of +, the zero of the dial, to be down, which is the proper condition of the apparatus when a message has to be dispatched. The operator having rung a bell at the distant end, to call the attention of the person who receives his message, begins to turn the handle, A, at the rate of about two revolutions per second. In this state of affairs no current is passing into the line, and the fingers of both his communicator and indicator remain stationary, as does also that of the indicator at the distant end of the line. Now, suppose he has to spell the word “FOX.” He turns the handle A continuously with his right hand the whole time he is sending the message; and, manipulating the keys with his left, he depresses that opposite to the letter F. By this action the key opposite + is raised, for the levers are pressed into notches against a watch-chain, which has just enough slack to allow one lever to enter a notch, and therefore the pressure of another lever always raises the key last depressed. When the operator presses down the F key, the + rises, the radial arm is instantly released, and with the index is carried on to F, where it stops; and the contacts will have, during that movement, sent six currents into the line, so that the fingers of both indicators will also point to F. When the pointer of the communicator has made just a visible pause at F, he pushes down the key of O, and all the three pointers recommence their journeys towards that letter. The operator must, of course, wait until they have reached it and paused an instant, when he depresses the button opposite X; and when the index has pointed at that, he pushes down the + key, whereby the fingers all arrest their movements at that point, indicating that the word is completed. In the case supposed the word is completed by a single revolution of the pointers; but this is, 570of course, not usually the case; thus, in indicating the syllable “PON,” nearly three complete revolutions would be required. This admirable little instrument was designed for the use of private persons, and is largely used in London and elsewhere. Its great compactness and simplicity of operation render it highly suitable for this purpose. There is no battery required, and all the inconvenient attention demanded by a battery is therefore dispensed with. On the other hand, the