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.

It is stated that a certain blind operator could read the signals by the smell of the chemical action; and we can well believe it.  In fact, the telegraph appeals to every sense, for a deaf clerk can feel the movements of a sounder, and the signals of the current can be told without any instrument by the mere taste of the wires inserted in the mouth.

A skilful telegraphist can transmit twenty-five words a minute with the single-current key, and nearly twice as many by the double-current key, and if we remember that an average English word requires fifteen separate signals, the number will seem remarkable; but by means of Wheatstone’s automatic sender 150 words or more can be sent in a minute.

Among telegraphs designed to print the message in Roman type, that of Professor David Edward Hughes is doubtless the fittest, since it is now in general use on the Continent, and conveys our Continental news.  In this apparatus the electromagnet, on attracting its armature, presses the paper against a revolving type wheel and receives the print of a type, so that the message can be read by a novice.  To this effect the type wheel at the receiving station has to keep in perfect time as it revolves, so that the right letter shall be above the paper when the