heroes of the telegraph-第17节
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as to imitate the motions of the needle。 But before it reached the Red Sea the cable had broken down； and the instrument was returned dismantled； to be superseded at length by the siphon recorder； in which the marking point is a fine glass siphon emitting ink； and the moving body a light coil of wire hung between the poles of a magnet。
The principle of the siphon recorder is exactly the inverse of the mirror galvanometer。 In the latter we have a small magnet suspended in the centre of a large coil of wirethe wire enclosing the magnet； which is free to rotate round its own axis。 In the former we have a small coil suspended between the poles of a large magnetthe magnet enclosing the coil； which is also free to rotate round its own axis。 When a current passes through this coil； so suspended in the highly magnetic space between the poles of the magnet； the coil itself experiences a mechanical force； causing it to take up a particular position； which varies with the nature of the current； and the siphon which is attached to it faithfully figures its motion on the running paper。
The point of the siphon does not touch the paper； although it is very close。 It would impede the motion of the coil if it did。 But the 'capillary attraction' of so fine a tube will not permit the ink to flow freely of itself； so the inventor； true to his instincts； again called in the aid of electricity； and electrified the ink。 The siphon and reservoir are together supported by an EBONITE bracket； separate from the rest of the instrument； and INSULATED from it； that is to say； electricity cannot escape from them to the instrument。 The ink may； therefore； be electrified to an exalted state； or high POTENTIAL as it is called； while the body of the instrument； including the paper and metal writing…tablet； are in connection with the earth； and at low potential； or none at all； for the potential of the earth is in general taken as zero。
The ink； for example； is like a highly…charged thunder…cloud supported over the earth's surface。 Now the tendency of a charged body is to move from a place of higher to a place of lower potential； and consequently the ink tends to flow downwards to the writing…tablet。 The only avenue of escape for it is by the fine glass siphon； and through this it rushes accordingly and discharges itself in a rain upon the paper。 The natural repulsion between its like electrified particles causes the shower to issue in spray。 As the paper moves over the pulleys a delicate hair line is marked； straight when the siphon is stationary； but curved when the siphon is pulled from side to side by the oscillations of the signal coil。
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 companiesthe Easternso 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 natureinto 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。
The recorder was first used experimentally at St。 Pierre； on the French Atlantic cable； in 1869。 This was numbered 0； as we were told by Mr。 White of Glasgow； the maker； whose skill has contributed not a little to the success of the recorder。 No。 1 was first used practically on the Falmouth and Gibraltar cable of the Eastern Telegraph Company in July； 1870。 No。 1 was also exhibited at Mr。 （now Sir John） Pender's telegraph soiree in 1870。 On that occasion； memorable even beyond telegraphic circles； 'three hundred of the notabilities of rank and fashion gathered together at Mr。
