VOLTAIC ELECTRIC! TV 



213 





wo can stop its tendency to oscillate, and make its deflections 

 -i^'ht or left of a more marked and cert tor. It 



is obvi lose movements, by being repeated and alter- 



. can bo made to represent a variety of distinct signals, 

 i number can bo chosen to represent the letters 

 alphabet, the numerals, and other necessary nigns, so 

 that words and sentences can be transmitted. Such, in brief, 

 is the single needle instrument, although, in its working form, 

 "f course, more conveniently arranged, the change of 

 >ii in the current being, for instance, managed by the 

 depression of two keys, which give the right or left-hand deflec- 

 tion of the needle as required. 



Morse key, which we select as the other representative 

 of Class I., works in a different manner altogether. In this case 

 we have no change in the direction of the current sent, but only 

 in it< duration. The key is simply a knob, the depression of 

 n lii.-H by the finger will cause contact to be made with tho 

 y, and so send a current along the line-wire. According 

 to the time for which the knob is depressed, so is the duration 

 of the current, and the signals therefore resolve themselves into 

 short and long impulses, technically called dots and dashes. 

 By making the dot to represent a left-hand movement of the 

 galvanometer needle, and a dash, or long impulse, a right-hand 

 movement, an alphabet used for the needle instrument is 

 readily adapted to the Morse key. At the receiving end of tho 

 line these dots and dashes can be read off in two different 

 ways. In the one case the message is recorded automatically 

 upon paper, in the other case the operator trusts to his ear 

 alone, although as a check there is generally a needle attached, 

 whose movements he can watch at the same time. The Morse 

 ink-writer in its simplest form consists of a little wheel at the 

 end of a lever, which is covered with printing ink. The lever 

 forms the armature of an electro-magnet, and is attracted to 

 that magnet whenever a current is sent through its coils. The 

 same movement causes the little ink-wheel to touch a band of 

 paper kept moving by means of clock-work. If the current be 

 ehcrt, the mark impressed upon tho paper is a dot, but if the 

 current be long, the wheel is of course kept for a longer time 

 against the paper, and a dash is the result. 



In what is known as the Morse sounder, the printing attach- 

 ment is dispensed with, and a spring armature, which gives a 

 click every time it is attracted towards the magnet, takes its 

 place. The experienced operator can read off the meaning of 

 these sound signals as easily as an ordinary person can com- 

 prehend speech ; but, as already stated, a galvanometer needle 

 is sometimes attached as a check on the correctness of his work. 

 According to Mr. Preece, sound-reading is steadily gaining 

 ground in this country. "There are," he says, "now 2,000 

 sounders ; in 1869 there were none. In America scarcely any 

 other instrument is used, but on the continent of Europe there 

 is scarcely one." We learn from the same authority with re- 

 gard to tho needle instrument that 3,791 are employed by the 

 Post Office, and that the different railway companies have in 

 use no fewer than 15,702. Although, as we have seen, the 

 needle instrument must be in skilled hands, its cheapness and 

 general efficiency render it peculiarly suitable for railway work. 



We will now select two instruments as representative of 

 Class II., where the signals are received, and in many cases also 

 printed, as ordinary letters of the alphabet. As our first ex- 

 ample, we may point to Sir Charles Wheatstone's ABC 

 instrument, which was so commonly used for private lines 

 before the advent of the telephone. This form of telegraph was 

 particularly well adapted for private use, not only because the 

 signals given were expressed by ordinary letters of the alphabet, 

 but also because it required no battery. The current was 

 afforded by a small magneto-electric machine, which formed 

 part and parcel of the instrument, and the mere act of keeping 

 a handle turning with one hand, while the other was employed 

 in signalling, caused a current to flow through the line-wire 

 whenever required. The action of the magneto-electric machine 

 will receive attention later on, and it is necessary here only to 

 refer to its existence in the ABC instrument now under dis- 

 cussion. Outwardly, the instrument has the appearance of a 

 mahogany box with a dial and pointer. Arranged round the 

 dial are the letters of the alphabet. The pointer moves as 

 required to tho different letters, and the same movements are 

 repeated on a similar dial at the other end of the line. As 

 already indicated, this instrument has been mostly used for 



short circuit*, but it hat been tried on a line 100 miles locf 

 wi-li SJMOsm 



The other instrument which we ecloct to illustrate tboe 

 contained under Chum II. in Hughe*' printing telegraph. In 

 thin itiHtrunient a little wheel having letters on iU edge revolve* 

 at an equal speed at either end of the line-wire. These wheels 

 are so arranged that the same letter on each if always in the 

 same position that in to say, supposing there is a fixed mark 

 at the lowermost part of each wheel, the tame letter will pa* 

 that mark at the name time as each revolves. By the action 

 of an electro-magnet, a little roller bearing a travelling strip 

 of paper is brought against the type wheel when required, and 

 a letter is printed without stopping the revolution of the wheel. 

 A scries of keys, like the keys of a pianoforte, each bearing a 

 letter of the alphabet, are so arranged that their depression 

 causes the particular letter which each represents to be printed 

 on the paper. Each wheel is driven by clockwork, and special 

 precautions are taken by mechanism we need not describe to 

 ensure that the action of both is synchronous. 



We therefore see that in all forms of electric telegraph the 

 signals are produced by two well-known effects of the elec- 

 tric current, the one being tho tendency of a magnetised 

 needle to place itself at right angles to a wire conveying 

 a current, and the other the circumstance that a piece of iron 

 becomes magnetic when a current flows through a coil of wire 

 surrounding it, the needle telegraph being an example of 

 one, and the Morse sounder and printer, and the Hughes 

 printing telegraph, being examples of the other. 



In the British postal telegraph system we find that there 

 are three forms of batteries in use namely, the Daniel!, the 

 Leclanche, and the Bichromate. The currents can be conveyed 

 overground, underground, or beneath the sea. Overground 

 wires are commonly seen by the side of our railways, our canals, 

 and many of onr country roads. The poles to support them 

 are in this country mostly of wood, but in onr colonies iron 

 supports are more commonly used. Iron wire is the material 

 in general use for conductors, but in the neighbourhood of large 

 towns, where smoke and corrosive vapours are prevalent, iron 

 is often replaced by copper. Another metal called phosphor 

 bronze, which possesses the conductivity of copper and the 

 strength of iron, is also coming into extensive use. Those 

 little porcelain knobs or cups, which are such familiar objects 

 on our telegraph poles, are to insulate the wires, so as to pre- 

 vent the current leaking to earth, as it certainly would do if 

 placed in contact with anything acting as a conductor of elec- 

 tricity. 



The underground lines, of which there are several thousands 

 of miles in the United Kingdom, we occasionally get a glimpse 

 of when under repair in our streets. The wires are of copper, 

 encased in gutta-percha, and bundles of them are hud side by 

 side in iron pipes, generally just below the curbstone of the 

 pavement. Underground lines are far more expensive than 

 overground lines, and it is estimated that if the whole of the 

 telegraphs if this country were so laid, it would involve an ex- 

 pense of twenty millions sterling. There is occasionally, when 

 wind and snow has broken down communication for a time, a 

 loud outcry that all wires should be laid below ground, but, aa 

 we have stated, the expense is almost prohibitory, besides 

 which there are technical reasons against such a course being 

 pursued. 



The art of laying submarine cables is now so well under- 

 stood, that there is seldom any failure in that operation. The 

 story of tho laying of the first cable across the bed of the At- 

 lantic is familiar to all ; we know how it parted and was picked 

 up again from the depths of the ocean, and how, finally, the 

 great work was completed. There are now more than 80,000 

 miles of such cables at work, and no fewer than nine different 

 lines span the Atlantic floor. The first enterprises of the kind, 

 with their difficulties and failures, have been studied and im- 

 proved upon with splendid results, and, although the cables as 

 now constructed are of much the same pattern as formerly, the 

 materials, from the inner metallic core to the outer protecting 

 skin, have been brought to such perfection in their manufacture 

 that the whole can be made to bear a breaking strain of little 

 less than one hundred tons to the square inch. The inner core 

 or conducting wire of the cable is usually made of the purest 

 copper that can be obtained, and for greater strength is con- 

 structed of seven wires twisted together. Next to this core 



