A .- J -.-. B -… K -.- C … L — D -.. M - - E . N -. F .-. O . . G —. Q ..-. H . .. R . .. I ..
S … 1 .—.
T - 2 ..-..
U ..- 3 …-.
V …- 4 ….-
W .- 5 —-
X .-.. 6 ……
Y .. .. 7 —..
Z … . 8 -.. ..
& . .. 9 -..-
Period ..—.. 0 ——
Comma .-.-
The International (Morse) code used elsewhere is the same as the above, with the following exceptions:
C -.-. Q —.- F . -. R .-. J .—- X -..- L .-.. Y -.— O —- Z —.. P .—.
FIG. 46.—Morse Signal Alphabet.
of the battery, in putting the line to one or the other, and thus making the "dot" signal with the positive and the "dash" signal with the negative pole. It follows that if the "dot" is indicated by a throw of the needle to the right side, a "dash" will be given by a throw to the left.
Most of the telegraph instruments for land lines are based on the principle of the electro-magnet. We have already seen (page 59) how Ampere found that a spiral of wire with a current flowing in it behaved like a magnet and was able to suck a piece of soft iron into it. If the iron is allowed to remain there as a core, the combination of coil and core becomes an electro-magnet, that is to say, a magnet which is only a magnet so long as the current passes. Figure 47 represents a simple "horse-shoe" electro-magnet as invented by Sturgeon. A U-shaped core of soft iron is wound with insulated wire W, and when a current is sent through the wire, the core is found to become magnetic with a "north" pole in one end and a "south" pole in the other. These poles are therefore able to attract a separate piece of soft iron or armature A. When the current is stopped, however, the core ceases to be a magnet and the armature drops away. In practice the electromagnet usually takes the form shown in figure 48, where the poles are two bobbins or solenoids of wire 61 having straight cores of iron which are united by an iron bar B, and A is the armature.
Such an electromagnet is a more powerful device than a swinging needle, and better able to actuate a mechanism. It became the foundation of the recording instrument of Samuel Morse, the father of the telegraph in America. The Morse, or, rather, Morse and Vail instrument, actually marks the signals in "dots" and "dashes" on a ribbon of moving paper. Figure 49 represents the Morse instrument, in which an electromagnet M attracts an iron armature A when a current passes through its bobbins, and by means of a lever L connected with the armature raises the edge of a small disc out of an ink-pot I against the surface of a travelling slip of paper P, and marks a dot or dash upon it as the case may be. The rest of the apparatus consists of details and accessories for its action and adjustment, together with the sending-key K, which is used in asking for repetitions of the words, if necessary.
A permanent record of the message is of course convenient, nevertheless the operators prefer to "read" the signals by the ear, rather than the eye, and, to the annoyance of Morse, would listen to the click of the marking disc rather than decipher the marks on the paper. Consequently Alfred Vail, the collaborator of Morse, who really invented the Morse code, produced a modification of the recording instrument working solely for the ear. The "sounder," as it is called, has largely driven the "printer" from the field. This neat little instrument is shown in figure 50, where M is the electromagnet, and A is the armature which chatters up and down between two metal stops, as the current is made and broken by the sending-key, and the operator listening to the sounds interprets the message letter by letter and word by word.
The motion of the armature in both of these instruments takes a sensible time, but Alexander Bain, of Thurso, by trade a watchmaker, and by nature a genius, invented a chemical telegraph which was capable of a prodigious activity. The instrument of Bain resembled the Morse in marking the signals on a tape of moving paper, but this was done by electrolysis or electro-chemical decomposition. The paper was soaked in a solution of iodide of potassium in starch and water, and the signal currents were passed through it by a marking stylus or pencil of iron. The electricity decomposed the solution in its passage and left a blue stain on the paper, which corresponded to the dot and dash of the Morse apparatus. The Bain telegraph can record over 1000 words a minute as against 40 to 50 by the Morse or sounder, nevertheless it has fallen into disuse, perhaps because the solution was troublesome.