The signals below the centre of the dial are indicated by the parallel movements of both needles simultaneously. Both needles moving once to the left indicate r; twice, s; thrice, t; first right than left with both, u; the reverse, v; both moving once to the right, w; twice, x; thrice, y.
The figures are indicated in the same way as the letters nearest to which they are respectively placed.
To change from letters to figures, the operator gives H, followed by the + which the recipient returns to signify that he understands.
If after the above signs (H and + ), were given, c, r, h, l, were received, 1845 would be understood.
A change from figures to letters is notified by giving I followed by the +, which the recipient also returns.
Each word is acknowledged; if the recipient understands, he gives e, if not the +, in which case the word is repeated. Stops are placed at z z, to limit the range of the vibrations of the needles. The connexion between the needles and the battery is made and broken by means of the handlesf f. Within the case g is contained an alarum, which is rung to give notice to the person stationed at the other end of the line, that a communication is about to be made. This is effected in a similar way to that by which the indicator in the first described telegraph is set in motion; opposite the lever of the detent is fixed a horseshoe bar of soft iron, round which is coiled a quantity of wire, which, when connected with a wire from a battery, becomes a powerful magnet, and attracting the detent lever releases the spring, and thereby sets the alarum in motion. A similar warning apparatus is attached to the first described telegraph.
A third arrangement of the electric telegraph is that invented by Professor Morse, and which is the one adopted in America.
The electro-magnet is the basis upon which this invention wholly rests in its present construction. The electro-magnet is produced by coiling around a bar of soft iron made in the form of a horseshoe (Fig. 1.) copper wire previously covered, (similar to bonnet wire,) and varnished to prevent metallic contact with each other and the iron (Fig. 2). The two terminations of the wire thus surrounding'the iron in a spiral form, are brought out at each end of the curved bar, and are connected one with the zinc pole of a galvanic battery, the other with the platinum pole. The battery being prepared in the usual manner with its corroding acid, produces galvanic electricity, which starts off from one pole of the battery, follows the wire around the soft iron, and returns to the other pole of the battery by the other wire, thus forming a complete circuit. The galvanic fluid is now passing the whole length of the wire, and while thus passing, the curved iron becomes a strong magnet. By connecting the two ends of the bent iron with a bar of similar soft iron, it will support many pounds weight. If while in this condition one of the wires is removed from the battery, the cross bar falls, and with it its weights, and the curved iron returns instantly to its original state. It is unmagnetized.
Complete the circuit, as at first, and in an instant it is again a magnet. If the battery is placed 100, or 1000, or 10,000 feet from the iron, yet when the one is connected with the other by intervening wires, the effect upon the magnet is the same, making it a magnet when the circuit is complete, and vice versā when it is broken. In this way power is produced at a point of considerable distance from the generating agent; and it is wholly at the command of the operator at the battery to make or destroy the power produced with the utmost possible rapidity.
The figures on the preceding page represent the most simple form of the electromagnet, with its appropriate machinery for telegraphic purposes. a represents a side view of an iron bar, surrounded with its coils of copper wire, standing upon a platform d; v being an upright arm secured to d, to which the magnet or soft iron is permanently fastened, by means of the bolt b b passing between the prongs of the curved iron, and through the board v, and the adjusting screw c. e is the projecting prong of the iron after it has passed through the coils, one only being seen. The other prong is directly behind e. g represents the end of the iron bar or keeper, extending back so far as to cover both the projecting ends of the horseshoe-formed magnet. The iron bar, or keeper, is fastened to the lever h h, which is delicately adjusted so as to rise and fall by a pivot at i; k represents a steel spring, supported at one end over the lever h h by the upright v, and passing through a loop l formed from a brass wire, the lower part of the brass wire being secured to the lever h by means of a screw at m. o is a hardened steel point, connected with the lever h h, and directly over the centre of the metallic roller t, in which a slight groove is made to correspond with the point of o. r represents the standard in which the axis of the roller t freely revolves.
The line s represents the paper in form of a riband passing from its coil between the roller and the point of o; n and p are the two extremities of the wire upon the magnet a.
Every part is now described, and from what has preceded the description, (bearing in mind that the battery, when in action, by forming a complete circuit with the wires n andp, converts the horseshoe bar into a powerful magnet,) the mode of writing by the instrument may be easily comprehended by what follows.
Complete the circuit, and instantly the cross bar g approaches the ends of the magnet e, until they meet in the direction of the arrow to. Break the circuit, and g is carried up in the direction of the arrow x, by means of the spring k. If to the roller t clock work is attached, to give it a uniform movement upon its axis, the paper s will move with the same uniform motion under the point o, then by completing the circuit the point o is brought down upon the paper, which is indented to such a degree as to make it perfectly apparent, and the point continues to mark it in that manner so long as the circuit is closed, but, upon breaking the circuit, the marking ceases, and the point o flies from the paper, which continues passing on.
If the circuit is closed and broken with the utmost rapidity, then a succession of dots and of spaces upon the paper appears.
If the circuit is successively closed and broken with less rapidity, short lines and intervening short spaces are made. If closed for a longer time, and broken in succession, then the marks become longer: so that dots, short lines, long lines, and short and long spaces, are made according to the time the circuit is closed, and the rapidity with which the paper moves under the pen.
An arbitrary arrangement of these dots, short and long spaces, and lines, constitutes the telegraphic alphabet, by means of which, intelligence to any extent is communicated. Thus one dot may represent a, two dots b, three dots c, one dot and a line d, etc. The paper to be imprinted, is fixed upon a revolving cylinder, and records despatches day and night; the records of the night may be examined in the morning. The alphabet is easily learned.