UNDDLATORY FORCES. ELECTRO-MAGNETISM. [ALIAS'S TEI.EOBAPH. 



he can safely remove from iU connections the telegraphic 

 portion of the menage system. By thii automatic 

 scheme, the attendant need not be always present He 

 may even go to bod ; and when he awakes he may find 

 the communications sent in the meantime in the message 

 basket Further, one attendant at each end of the lino 

 wire is all that is now needed ; and the sender need be 

 no other than a person of average intelligence, of little 

 experience, and who can, as has been already said, read 

 well A boy or girl of twelve or fourteen years may do 

 the sending work ; and a moderate education and ex- 

 perience are all that is needed to receive, interpret, ex- 

 tend in writing, and distribute correspondence. A 

 uniform charge for messages within a wide circuit belongs 

 to the economy of this system, upon the basis of the 

 plan adopted for our post-office. The Telegraph Com- 

 pany, according to Mr. Allan's scheme, should issue 

 blank and file books ; and any person possessing one 

 such book, lias only to write his message on a blank 

 leaf, tear it out, envelope, and drop it into the office- 

 box, when it has instant attention given to it All this 

 appears quite plain and possible, but the distinguishing 

 features of the mechanism, conjointly with the electrical 

 influence by which it is produced, is not so obvious. 

 According to Allan's plan of signalling, the punctures or 

 "embossings," on the paper at the receiving points, are 

 made by the method of reverse currents, or the positive 

 and negative electric currents are both made effective for 

 marking ; and the receiving instrument itself, without 

 any expense of power, makes the distinguishing spaces 

 between the letters ; whereas, in other instruments of this 

 kind, small spiral springs are introduced, for the quick 

 and certain recovery of the deflected needle to the neutral 

 position, in order to make spaces. This latter plan is also 

 followed by Digney, a French maker of good repute ; but 

 it is objectionable for various reasons ; and one of these is 

 the superfluous demand that is made on the electric 

 force to overcome a mechanical resistance, and the pos- 

 sible fluctuations and depressions of battery force, which, 

 from the resistance of the spring, might destroy the 

 signalling power. In tlio instances of the telegraphic 

 instruments of other makers, reverse currents are em- 

 ployed instead of springs ; but, with them, one of the 

 currents is devoted to making the spaces, whereas Allan 

 utilises both, as has been already stated, for marking. 

 By this means he diminishes the number of currents 

 sent through the line wire by upwards of 30 per cent. ; 

 :iml, on the other hand, the gain in point of time, by 

 adopting altogether the " dov' system of marking, is 

 about 50 per cent. This particular will be at once appre- 

 ciated by the intelligent telegraphist at its proper im- 

 portance, because, by the arrangement in question, 

 greater signalling power is attained with relatively less 

 expense of electrical force ; and besides this, and with 

 especial reference to the application of this plan to long- 

 range submarine telegraphy, greater speed of transmission 

 is also attained. But further, the effective workings of 

 such instruments depend, amongst other things, upon 

 the nice adjustment and suitable condition of the 

 metallic surfaces, which are required to act by making 

 and breaking electrical contact with each other. First, 

 the sending or reversing break is here made to preserve 

 clean contact by n rubbing action, which effectually 

 wipes off any abraded matter which the spark carries 

 over from one terminal point, and deposits upon the 

 other and opposite point In Allan's "relays," or pole 

 changers, as these instruments may bo called, this con- 

 tingency is very ingeniously provided against. The 

 relays are " sparkless ;" and the small disruptive dis- 

 charge of electricity which takes place on breaking con- 

 tact i-s not produced in the relay at all, but in the 

 recording instrument, where the mutual attrition of the 

 metallic surfaces constantly preserves the parts o! 

 The importance that attaches to this particular will be 

 apparent, when it is remembered that foul contact-points 

 in the relay would soon reduce the action of the battery, 

 which should work it, to inefficiency. By Allan's plan 

 the power of the battery is preserved, and the niochim -ry 

 of the whole Line kept open for the transmission of cor- 



j respondcncc. Moreover, the absence of the spark in the 

 relay admits of a great increase in the power of the local 

 j battery, and therefore of more efficient action in working ; 

 whereas the sparkling relay of other makers compels 

 them to use only a very moderate power, so as to injure 

 the operations of the instrument as little and as slowly 

 as possible. This inconvenience, therefore, carries with 

 it a limit upon the energy with which a telegraph line 

 can bo worked, without the risk of delaying its action, 

 for cleaning the relay at very short intervals of time. 



The above gives a general description of Mr. Allan's 

 signal arrangements : we shall no.v refer to his im- 

 provements in the construction of cables, especially those 

 intended for deep-sea working. Near shore, Mr. Allan 

 uses cables of considerable comparative thickness, so as 

 to avoid the danger which always arises from the abrasion 

 by rocks, and other sources of injury. Tht following 

 observations, for which we are indebted to a valuable 

 periodical, the Electrician, will afford the reader an 

 insight into the improvements claimed for Mr. Allan's 

 cable. 



' ' Mr. Allan claims for his principle of deep-sea telegraph 

 cable, that it combines the maximum of conducting power, 

 insulation, strength, flexibility, and durability, with the 

 minimum of weight, bulk, cost, and risk in submergence. 

 He adopts the solid copper wire as giving the greatest 

 amount of conducting power, with the least amount of 

 inductive surface. The strand of copper wire used for 

 ordinary forms of cable, presents considerably more surface 

 than would bo obtained with the same amount of con- 

 ductivity in a solid copper wire ; but it is found safer to 

 sacrifice a small amount of speed, owing to the incr. 

 surface, than to run the risk of a fracture in the solid 

 copper conductor. Having obtained the best soft solid 

 copper wire, he surrounds it with small steel wires of the 

 best quality, laid on with a slight spiral ; and this forms 

 the inexteusible core or conductor, and also the strength 

 of the cable. This core, or backbone of tho cable, is 

 then insulated with separate layers of gutta-percha, or 

 iinlia-rubber, or any other combination of tho two; but 

 it is Mr. Allan's opinion that none of the failures in deep- 

 sea cables ought to injure the reputation of gutta-percha 

 as an insulator ; and his confidence in its suitability for 

 submarine telegraphy remains unshaken, provided it bo 

 applied to the conductor with the necessary amount of 

 care, and not submitted to any crushing or stretching 

 process before it reaches its ocean bed. Tho insulated 

 core is then clothed with a slight covering of hemp, or 

 any other cheap material, saturated with marine paint ; 

 and this completes the deep-sea cable, 



" Tho true mechanical test of a submarine cable is to 

 ascertain the number of fathoms of its cr.vn length it will 

 sustain iu water without elongating to any serious extent. 

 If the conductor, or metallic portion of tho cable, be 

 small, then the cable may sustain an enormous length of 

 its own weight in water, and still not be at all suited for 

 a longdistance, because of the insufficiency of condu 

 power. In this respect Mr. Allan's cables wore excellent 

 examples, with a much larger conductor than most of the 

 other light cables sent in for testing. Mr. Allan's bore a 

 weight nearly equal to 7,500 fathoms without elongating 

 one per cent ; and this may be taken as the weakest link 

 in the chain, for joins in the steel wire abounded. This 

 cable was also tested round a 12-inch wheel, to see if tho 

 core would cut through tho gutta-percha ; and although 

 this ordeal was at least ten times more severe than it 

 could be subjected to in submergence, not the slightest 

 deviation from the centre could be detected." Tho fol- 

 lowing is the report after tho experiments were conducted 

 (Government Report, page 28). "The results shown in 

 the above table for Mr. Allan's cables are remarkable. 

 In these cables the strength is given by steel wires laid 

 spirally round tho copper conductor, thus using tho 

 strength-giving material to form part of tho conductor ; 

 tho area of the conductor is therefore increased ; and 

 there is no danger of the conductor knuckling through 

 the gutta-percha from the resiliency of tho latter. This 

 addition to the conducting area increases tho induction 

 of tho cable iu the full ratio of the increased area, but it 



