It is to the mouse-mill that me must look both for the electricity which is used to electrify the ink and for the motive power which drives the paper. This unique and interesting little motor owes its somewhat epigrammatic title to the resemblance of the drum to one of those sparred wheels turned by white mice, and to the amusing fact of its capacity for performing work having been originally computed in terms of a 'mouse-power.' The mill is turned by a stream of electricity flowing from the battery above described, and is, in fact, an electro-magnetic engine worked by the current.
The alphabet of signals employed is the 'Morse code,' so generally in vogue throughout the world. In the Morse code the letters of the alphabet are represented by combinations of two distinct elementary signals, technically called 'dots' and 'dashes,' from the fact that the Morse recorder actually marks the message in long and short lines, or dots and dashes. In the siphon recorder script dots and dashes are represented by curves of opposite flexure. The condensers are merely used to sharpen the action of the current, and render the signals more concise and distinct on long cables. On short cables, say under three hundred miles long, they are rarely, if ever, used.
The speed of signalling by the siphon recorder is of course regulated by the length of cable through which it is worked. The instrument itself is capable of a wide range of speed. The best operators cannot send over thirty-five words per minute by hand, but a hundred and twenty words or more per minute can be transmitted by an automatic sender, and the recorder has been found on land lines and short cables to write off the message at this incredible speed. When we consider that every word is, on the average, composed of fifteen separate waves, we may better appreciate the rapidity with which the siphon can move. On an ordinary cable of about a thousand miles long, the working speed is about twenty words per minute. On the French Atlantic it is usually about thirteen, although as many as seventeen have sometimes been sent.
The 'duplex' system, or method of telegraphing in opposite directions at once through the same wire, has of late years been applied, in connection with the recorder, to all the long cables of that most enterprising of telegraph companies--the Eastern--so that both stations may 'speak' to each other simultaneously. Thus the carrying capacity of the wire is in practice nearly doubled, and recorders are busy writing at both ends of the cable at once, as if the messages came up out of the sea itself.
We have thus far followed out the recorder in its practical application to submarine telegraphy. Let us now regard it for a moment in its more philosophic aspect. We are at once struck with its self-dependence as a machine, and even its resemblance in some respects to a living creature. All its activity depends on the galvanic current. From three separate sources invisible currents are led to its principal parts, and are at once physically changed. That entering the mouse-mill becomes transmuted in part into the mechanical motion of the revolving drum, and part into electricity of a more intense nature--into mimic lightning, in fact, with its accompaniments of heat and sound. That entering the signal magnet expends part of its force in the magnetism of the core. That entering the signal coil, which may be taken as the brain of the instrument, appears to us as INTELLIGENCE.
The recorder is now in use in all four quarters of the globe, from Northern Europe to Southern Brazil, from China to New England. Many and complete are the adjustments for rendering it serviceable under a wide range of electrical conditions and climatic changes. The siphon is, of course, in a mechanical sense, the most delicate part, but, in an electrical sense, the mouse-mill proves the most susceptible. It is essential for the fine marking of the siphon that the ink should neither be too strongly nor too feebly electrified. When the atmosphere is moderately humid, a proper supply of electricity is generated by the mouse-mill, the paper is sufficiently moist, and the ink flows freely.
But an excess of moisture in the air diminishes the available supply of EXALTED electricity. In fact, the damp depositing on the parts leads the electricity away, and the ink tends to clog in the siphon. On the other hand, drought not only supercharges the ink, but dries the paper so much that it INSULATES the siphon point from the metal tablet and the earth. There is then an insufficient escape for the electricity of the ink to earth; the ink ceases to flow down the siphon; the siphon itself becomes highly electrified and agitated with vibrations of its own; the line becomes spluttered and uncertain.
Various devices are employed at different stations to cure these local complaints. The electrician soon learns to diagnose and prescribe for this, his most valuable charge. At Aden, where they suffer much from humidity, the mouse-mill is or has been surrounded with burning carbon.
At Malta a gas flame was used for the same purpose. At Suez, where they suffer from drought, a cloud of steam was kept rising round the instrument, saturating the air and paper. At more temperate places the ordinary means of drying the air by taking advantage of the absorbing power of sulphuric acid for moisture prevailed. At Marseilles the recorder acted in some respects like a barometer. Marseilles is subject to sudden incursions of dry northerly winds, termed the MISTRAL. The recorder never failed to indicate the mistral when it blew, and sometimes even to predict it by many hours. Before the storm was itself felt, the delicate glass pen became agitated and disturbed, the frail blue line broken and irregular. The electrician knew that the mistral would blow before long, and, as it rarely blows for less than three days at a time, that rather rude wind, so dreaded by the Marseillaise, was doubly dreaded by him.
