38 



NATURE 



\Nov. 14, 1878 



The small carbon is pointed at its upper extremity and 

 retains this point while burning. A small electric arc is 

 formed round the points of junction, and to this is due 

 the greater part of the light and not to incandescence alone. 

 The carbons are kept in contact by chains attached to 

 the lower end of the pencil passing over pulleys and 

 down again to a weight of about i^ lbs., which is 

 sufficient to keep the pencil pressing gently against the 

 disc. 



The sketch. Fig. i, shows the arrangement of the 

 lamp ; a is the negative carbon, connected by the 

 semicircular piece of metal f to the conductor e on the 

 right-hand side which forms part of the lamp-post. The 

 metal / is hinged so that the top carbon may be moved 

 back when a globe is put on. b is the pencil or 

 positive carbon sliding in the tube c, this tube being con- 

 nected to the conductor e on left-hand side. The pressure 

 of the contact upon the small carbon is regulated by the 

 spring d. The tube is shown in perspective for greater 

 clearness. The arrangement and details of the lamp 

 being thus shown, we will now describe the experiments 

 which hare recently been exhibited at the works of the 

 British Telegraph Manufactory in the Euston Road. 

 The display was mostly of an experimental character, 

 the lamps being somewhat different in construction to 

 those which will be made use of in actual practice, but the 

 principle remains the same. The chief object of the 

 inventor was to demonstrate that a number of lights can 

 be steadily maintained in one circuit. The first experi- 

 ment tried was that of putting two large lamps such as 

 will be used for street-lighting in circuit with a Gramme 

 electro-plating machine. It may be here remarked that 

 this is probably the first time that such a machine was 

 ever used for the purpose of producing an electric light. 

 The two lamps were said to give a light equal to 360 

 candles each, but they gave to all appearance a conside- 

 rably higher illuminating power. 



A pure white light was given out, perfectly steady, and 

 showing none of the blue or purple rays observed so fre- 

 quently in the ordinary form of electric arc. The wonder- 

 ful steadiness of the light is one of its chief features. After 

 burning for some considerable time the current was 

 switched on to a row of ten smaller lamps arranged on a 

 shelf. The light from each lamp was apparently of the 

 same strength and the effect was very brilliant, but the 

 total illuminating power was not nearly so great as in the 

 case of the two larger ones. But it seemed to show that 

 a form of light had been devised that could be split up 

 into a considerable number of smaller ones, each of 

 which could be made use of in a practical way. The ten 

 lamps were estimated to have a lighting power of forty 

 candles each, but this is probably somewhat above the 

 mark. But the results obtained, both as regards the 

 wonderful regularity of the lamps and the practical de- 

 monstration of dividing the light, seem to have been 

 satisfactory ; and the more remarkable from the fact of 

 the weak electro-motive force of the machine, which is 

 only equal to that of four Daniell's cells. More lamps 

 could have been lighted even from this machine had they 

 been at Mr. Werdermann's command, but of course with 

 a diminution of light. When suitable machines have 

 been constructed Mr. Werderman is confident of being 

 able to put 50 or 100 lights in circuit, but he does not 

 telieve in the indefinite division of the current for 

 lighting purposes. 



The lights were all connected parallel, as shown in 

 diagram, Fig. 2. The thick wires -f- and — connect the 

 lamps with the machine, the first lamp on the -}- cable 

 being last on the — wire. The spirals a are extra resist- 

 ances put in the circuit of each lamp, the object being to 

 render the divided current less sensitive to any slight 

 variation in the resistance of the lamps themselves, due 

 to unequal pressure of contact, &c. The resistance of 

 each lamp, including the wire a, is about o'39 ohms. The 



resistance of the ten in parallel circuit about 0*037 ohms J 

 The carbon pencil consumes at the rate of from i^ to 

 2 inches per hour in the small lamps ; the large ones taking 

 4^ millimetre carbons, consume about i\ or 3 inches in 

 the same time. The pencils are made in Paris, costing 

 about I franc per yard, which length will last for twelve 

 hours. The discs are of ordinary carbon. 



However many lights may be in use, one, two, three, 

 or any number can be put out without affecting the 

 others, the regulation of the current being provided for 

 by a switch attached to each lamp. But if necessary, the 

 current which originally went through those that are ex- 

 tinguished can be added to those kept alight, of course 

 increasing their illuminating power. The lamps are set 

 in action simultaneously, can be as easily put out, and 

 again re-lighted. 



Returning again to the intensity of the light, it was 

 stated that the large lamps were equal to 360 candles. 

 Now the effect of this light upon the eyes is apparently 

 not injurious, and it is Mr. Werdermann's intention to 

 use only globes of ordinary glass, as in the present form 

 of gas-lamps ; by this means the loss of light will be very 

 slight indeed as compared with other systems, where the 

 loss is from 20 to 30 per cent., incurred by using opal or 

 ' ground glass globes. ; 



Owing to the very small electromotive force of the 

 machine the insulation of the cables can easily be pro- 

 vided for, and Mr. Werdermann hopes, with sufficiently 

 powerful machines, to be able to carry the current to a 

 considerable distance without any appreciable loss. 



In conclusion, it may be worth while giving a few 

 details in regard to the Gramme machine used. It is an 

 electro-plating machine of the old pattern, having four 

 upright electro-magnets and two bobbins, one for feeding 

 the electro-magnets, the other for taking off the light- 

 producing current. The bobbins are wound with thick 

 copper bands. The electromotive force, as before stated, 

 is only equal to four Daniell's cells, and the resistance of 

 the taking-off bobbin is about o-oo8 ohms. The quantity 

 of current produced is of course large. 



It may be mentioned that the large lamps were con- 

 nected parallel, but having no extra resistances, as in the 

 case of the 10 ; their resistance is also a trifle less. 

 The resistances given are when the lamps are not alight ; 

 when burning it would be somewhat less. The power 

 required to drive the machine described is about two 

 horse-power. 



A curious fact about the light is that the top carbon is 

 not consumed, or at any rate so slowly, that it is not 

 noticeable ; therefore, to all intent and purpose, the lower 

 carbon only is wasted. 



T. E. Gatehouse 



DUPLEXING THE ATLANTIC CABLE 



THE simultaneous transmission of two telegraphic] 

 messages in opposite directions upon one wire, now] 

 known by the name of duplex telegraphy, dates back 

 from the year 1853. In that year Dr. Gintl, the director 

 of state telegraphs in Austria, described a rnethod by 

 which this feat could be accomplished, and in July of 

 the same year the method suggested by Gintl was tried 

 between Prague and Vienna. An improvement on this 

 method was suggested by a German electrician, Frischen, 

 by Messrs. Siemens and Halske, of Berlin, and other 

 workers at this subject. Nevertheless, owing to practical 

 difficulties, the experiments were little more than interest- 

 ing additions to our knowledge. So little hope, indeed, 

 was there of the practical realisation of this important 

 matter that, in a standard work on telegraphy, published 

 in 1867, after describing the early methods of duplex 

 telegraphy, the author remarks :— " Systems of telegraph- 

 ing in opposite directions and of telegraphing in the same 



