HI 



I'ULATORY FORCER ELECTRO-MAGNETISM. [PRIJTTJXO TELBORAPHS. 



Tho effect of ordinary terrestrial electric current* on 

 the submarine cable, cannot tie properly iwortained ; for 

 f a cable submerged in a liquid of tolerable 

 conducting power, includes so many elements of dis- 

 turbance, as to preront the possibility of our acquiring 

 accurate or reliable data. 



The remarks which we have just made, apply 

 equally to all siibm.irine cables ; and are modified by the 

 difference of their length, the thickness of the con- 

 ducting wire, and the number of them enclosed in the 

 It would be very desirable if a scries of simulta- 

 neous observations were made, as to the retardation 

 which is exercised on a current at tho same moment, on 

 cables laid in different directions, with respect to the 

 compass. It would thus be seen how far electric or 

 magnetic currents affected tho conducting power, and 

 whether such had a definite direction and action under 

 all circumstances. 



We shall now describe tho construction of various 

 kinds of telegraphic instruments which have been in- 

 vented during the last few yean, on principles entirely 

 different to that of the needle apparatus. 



ELECTRO-PRINTING TELEGRAPHIC 

 INSTRUME.N 



THK remarks we have hitherto made, have referred 

 entirely to the uoedle instrument, or to circumstances 

 which affect every form of telegraph apparatus, so far as 

 the conducting medium is concerned. We shall, therefore, 

 pass on to examine a variety of arrangements in use in 

 different countries, and also, to a limited extent, in our 

 own. 



The needle instrument only indicates, and docs not 

 record, a message. As we have fully explained, the signals 

 are effected by means of alternate or combined deflections 

 of a magnetised needle ; and its use is practically confined 

 to those who ore accustomed to it, and can, therefore, 

 readily translate its signs. This, to some extent, is an 

 objection, and limits its use. If letters and words were 

 imprinted by it, then its indications would be intelligible 

 to any one ; and its use would doubtless be more general. 

 It is also liable to many derangements. The needles may 

 lose their magnetic power, and, in curtain instances. 

 perhaps, at the very moment when they may be most 

 required : a sudden flash of lightning inverts tlieir 

 polarity, and all attempts to employ them are futile. 

 Earth currents, and atmospheric influences, also combine 

 to effect their derangement. 



These, and other reasons, have led to the invention of 

 printing telegraphs; by means of which, the words of 

 which a message is composed are spelt and printed on 

 cloth or paper ; or, which answers the same purpose, dots 

 and dashes of various lengths are printed, according to a 

 preconcerted code of signals. 



Wo shall first describe the general principles on which 



ilcal printing telegraphs are constructed ; then refer 



to tho mechanism by which the plan is carried out ; 



and shall best illustrate our subject by suggesting some 



experiments bearing on it. 



iment 22. Dissolve a little yellow pnissiate of 

 potass iu warm water ; and also, in a separate gloss, some 

 crystals of sulphate of iron (green copperas). Add these 

 two solutions together: a blue precipitate will be pro- 

 duced, which is commonly called Prussian blue. Now, 

 it is by the production of this colour on paper or cloth, 

 that tho printing of dots, dashes, or long lines, is effected 

 in some kinds of telegraplis. The mode of printing may 

 be illuHtrutcd as follows. 



nt 23. Moisten a piece of white calico with 

 a solution of sulphate of soda ; and, after wringing it, dip 

 it into a weak solution of tho prussiate of potass. 1 

 the cloth, whilst damp, on a sheet of tinfoil, and to this 

 attach the wire proceeding from tho copper plato of a 

 voltaic battery. Attach tho wire from tho zin. 

 kiiittiiiK-neodle, and draw tho end of tho needle over tho 

 moist cloth. Wherever it touches tho cloth, a blue 

 will bo left. If the needle just touch tho cloth by the 

 point, then a dot is produced ; but if tho point be drawn 



over the cloth, then a dash or long line is afforded. Now, 

 on exactly similar principles, and by a simple mci 

 tiou of the plan, meitsagos may be readily transit, 

 between any two stations the printed paper or cloth 

 kept, and the marks on it translated into ordinary 

 J..ii, MfK 



lo familiarise the mind of our readers with the prin- 

 cipal mechanical part of tin- printing apparatus, we will 

 suppose that a pianoforte key, made of metal, and with 

 one of its ends attached to tho wire of the < 

 a voltaic battery, is so arranged, as that, when pressed 

 ih'wn, it shall enter a small cup containing mereury. 

 From this cup wo will suppose a wire to extend to a 

 needle, placed so as to rest with its point against a metal 

 roller covered with cloth, which has been impregnated 

 with the prussiato of potass ; and that tho roller is con- 

 nected with another wire proceeding from tho zinc plate 

 of the voltaic battery. It is evident, that when the 

 pianoforte key is pressed into the mercury cup, a circuit 

 will be established ; a current will pass ; and the point of 

 the noodle will instantly impress a blue dot on the cloth 

 thus, . If, however, tho roller be gently moved, t 



instead of a dot, a dash , or long lino , will 



bo produced; the length depending on the length of 

 time the key is kept pressed down, so as to continue the 

 passage of the current. The instant the key is removed 

 from the mercury cup, tho current will cease to pass, and 

 no effect will be produced on the distant roller. Now, 

 this is exactly what happens in most of the chemical 

 printing telegraphs : but we may be better understood if 

 we refer to tho following engraving, which atlbrds an 

 illustration of the most essential pait of the apparatus. 



rig. so. 

 a 



In the above cut, we have a representing the roller on 

 which the prepared cloth is wound ; b is the needle which 

 imprints a dot, dash, or line ; c is a binding-screw, to 

 which is attached a wire, 10, extending to the copper 

 plate of tho battery, h. A wire is attached to the zinc 

 of the battery, and reaches to a small peg, g ; f is a key, 

 which, when pressed down on q, completes tho circuit. 

 The current will then travel from tho battery by the 

 wire vi, to the needle, and thence by the roller to tho 

 wire, w' ; returning again, through the key arrange- 

 ment, to the zinc of the battery. Of course, no mark is 

 made on the roller, except when tho key, /, is brought 

 into contact with the peg, <j. The roller is gently 

 turned by clockwork; or by hand, if for elementary 

 experiments. 



We have entirely avoided all mechanism used in the 

 complete apparatus, so that our readers might gather a 

 general knowledge of the modut opentiuli, ami, if they so 

 please, construct a model for their own use. Ha 

 thus illustrated the principle, we shall now describe 

 the various forms of apparatus which have been, or 

 are in use, constructed on such plans as we have 

 explained. 



Before doing so, we may call attention to a very in- 

 genious piece of apparatus invented by Mr. Whitehouse, 

 of Brighton, formerly the chief electrician to tho 

 Atlantic Telegraph Company; by which music could bo 

 printed as it was played on a pianoforte or harmonium, 

 it any distance from the instrument, and accurate as to 

 notes and time. Und< T ,i.-!i key of the piano a wire 

 was placed, whieh extended to a needle fixed to an 



itns similar to that which wo have just illustn. 

 On tho roller a long ship . .1" doth was placed, on which 

 as many needles pressed as there were keys on the piano. 

 loth was marked with the lines and spaces for bass 

 and treble, as is common in printed music; and by 

 means of clockwork, or by the hand, it was gradually 

 unwound from the roller. A current of electricity 



