872 EEPORT— 1892. 



3. Secondarij Batteries ill use at the Central Telegraph Office, London, for 

 Telegraphic Purposes. Bi/ W. H. Peeece, F.B.S. 



In a paper entitled ' The Use of Secondary Batteries in Telegraphy,' com- 

 municated to the British Association at the meetiug held at Montreal in 1884, an 

 account of a series of experiments was given whicli had been carried on during 

 the preceding twelve months to determine the suitability of secoadary batteries 

 for telegraphic purposes. 



Since that time the use of secondary batteries has been extended, and for the 

 past seven years they have been used to supply current to two large groups of 

 circuits, one group consisting of 110 single needles, and the other of 100 Morse 

 inkers and sounders. 



To provide a ready means of replacing the battery in case of failure, the leads 

 from the working and reserve cells, which are placed in the basement, are first led 

 up to the test-board in the instrument room, and there joiaed to a switch ; thence 

 the leads are again led to a test-board in the battery room, where the two groups 

 are split up into sub-groups of ten circuits each. The connections are made in 

 this manner for two reasons : first, for facilitating a change of a faulty battery, and 

 second, to prevent a general stoppage of the whole group in the event of a short 

 circuit at any of the instruments, tlie resistance of the leads between the instru- 

 ments and the subdividing connections in the basement beiug sulHcient to prevent 

 more than three amperes being taken from the battery by any one of the instru- 

 ments, even when a short circuit is on. To prevent any damage to the instruments 

 or risk of fire fuses are placed in the battery leads at each instrument. 



The circuits on the groups mentioned are all metropolitan, and are all, 

 approximately, of the same resistance, no equalising resistances being therefore 

 necessary. The current in each circuit ranges between seventeen and twenty 

 milliamperes. 



The E.M.F. for the single needles is twenty volts, ten cells positive and ten 

 cells negative, with earth in the centre. For Morse working the E.M.F. is 

 eighteen volts. 



In addition to these two groups another set of twenty-two cells has been in 

 use since 1889, supplying current for driving the motors of the Delany multiplex 

 distributors. Each of these motors requires a current of about -12 ampere, and 

 there are ten of them at present driven from this source. Fuses are placed in the 

 leads to each motor. There is no spare set for this work. 



A considerable extension of the accumulator system has recently been made, 

 advantage being taken of the transfer of all the Continental service to the General 

 Post Office building in St. Martin's-le-Grand. This transfer was made on 

 October 17, 18!)1, and since that date the whole of the Continental circuits have 

 been operated by currents from secondar}- cells. 



There are fifty-nine of these Continental circuits, and as they are of various 

 lengths, some requiring repeaters in England, whilst others go direct to the 

 Continent, a somewhat different arrangement has been adopted. In addition to 

 these varying conditions it was found Impossible to use the same polarity in all 

 countries, the German, Dutch, and Belgian lines taking positive, and the French 

 negative. 



It was also necessary to provide an arrangement which would cause the stop- 

 page of the minimum number of lines should a main fuse be burned or a battery 

 fail. 



The fifty-nine lines are divided into four groups ; but as the force required for 

 these long lines is 100 volts it is evident that the risks of allowing a dangerously 

 heavy current passing out from the instrument to line, should it make earth neaV 

 the sending station, are increased. To provide against this, resifitances of 100 volts 

 are placed in the battery leads at each instrument, so that it is absolutely im- 

 possible that more than one ampere can flow even with earth on the line close up 

 to the instrument. Independent three-ampere fuses are also fitted to each instru- 

 ment to prevent any damage to lines or instruments should the safety resistance 

 be short-circuited. 



