490 



NATURE 



[September 24, 1891 



Two separate buildings are devoted respectively to 

 electrical railway signalling and to telegraphic and tele- 

 phonic exhibits. The Government have contributed an 

 interesting collection of historical telegraphic appa- 

 ratus, from which it may be seen that the signalling 

 instruments have been going through the same sort of 

 evolutionary changes in Germany as in England, with this 

 difference, however, that our apparatus has reached a 

 much later stage of development than theirs. The Ger- 

 man telegraph wires have been well erected, although 

 less attention than would satisfy an English telegraph 

 engineer has been paid in obtaining that perfect symmetry 

 in the hanging of the wires which is necessary to avoid 

 contacts being produced between them as they are 

 swayed backwards and forwards by the wind. The 

 underground wiring is especially good, but the methods 

 of testing and signalling are antiquated, and the routine 

 of the Telegraph Department generally is fettered with 

 red tape. 



There is one detail, however, in connection with the 

 German Post Office, that forces itself on the admiration 

 of the foreigner. If you desire to send money, you hand 

 in the sum at the post-office, with a postcai-d costing 

 2^(/, which youaddresstoyour correspondent with details 

 of the sum sent, and receive a receipt in exchange. But 

 you need write no letter, send no postal order nor receipt, 

 nor trouble your correspondent to go to the post-office ; 

 the postman delivers to your correspondent at his house 

 or office your postcard, and in return for half of it hands 

 him at once in cash the sum of money sent. 



The display of telephonic apparatus at the Exhibition 

 is large and complete, but owing to the activity of the 

 commercial traveller of the day in keeping English 

 engineers acquainted with practically all that is being 

 done abroad, there is little that strikes the English tele- 

 phone engineer as new. A new telephone exchange 

 switch-board, constructed by Messrs. Mix and Genest, 

 contains, however, a point of novelty, and a switch-board 

 of this description has just been adopted at the Berlin 

 Telephone Exchange. 



The general arrangement of an exchange switch-board 

 is as follows :— The wires from all the subscribers are 

 brought to all the clerks at the exchange, so that it is 

 possible for any clerk to connect any subscriber with any 

 other, to enable the two subscribers to talk to one another. 

 The calls, however, from certain subscribers only are re- 

 ceived by any particular clerk ; for example, of all the 

 wires coming to clerk A, only those from, say, i to loo 

 are provided with drop shutters, so that if any subscriber 

 from I to 100 rings up the exchange, one of the drop 

 shutters in front of clerk A will fall, whereas if a sub- 

 scriber from 200 to 300 rings up the exchange, it will be a 

 drop shutter in front of clerk C that will fall. Each clerk, 

 therefore, deals with the calls from a certain set of sub- 

 scribers only, but this clerk may have to connect any one 

 of this set of subscribers with any other of the same set 

 or with any subscriber of any of the other sets ; since, of 

 course, any subscriber to the exchange has the right to 

 be put in communication with any other. 



Suppose, now, that clerk A receives a request from 

 subscriber 85 to be put in communication with subscriber 

 560, the first thing to find out is whether the line of sub- 

 scriber 560 is free, or whether it has been already con- 

 nected with some other subscriber by one of the other 

 clerks. This is usually ascertained by means of what is 

 known as a "testing wire," which permeates all the 

 switch-boards of all the clerks, and enables any clerk to 

 see whether any line coming into the exchange is free or 

 not. But in a large exchange the running of this testing 

 wire throughout all the switch-boards necessitates the 

 employment of many miles of wire, and it is to avoid this 

 that Messrs. Mix and Genest have adopted the following 

 new device : — 



The ends of the plugs which the clerk presses into the 



NO. 1 143, VOL. 44] 



various holes, or " spring jacks " as they are technically 

 called, for the purpose of connecting one subscriber with 

 another, are made electrically in two parts, the tip of the 

 plug being insulated from the remainder by a piece of 

 ebonite ; a couple of cells are joined up at the exchange 

 to each pair of plugs, in such a way that on inserting the 

 tip of the second of a pair of plugs into a spring jack, an 

 instantaneous current passes, deflecting the needle of a 

 galvanoscope if the second line be free. For example, 

 clerk A receives a call from subscriber 85 to connect him 

 with subscriber 560 : he inserts one of a pair of plugs into 

 the spring jack 85, he then inserts the second plug into 

 spring jack 560, and as the top of this second plug enters 

 the spring jack there will be an instantaneous swing of 

 clerk A's galvanoscope if line 560 be free, in which case 

 the clerk pushes the plug home, and completes the con- 

 nection between subscribers 85 and 560. If, however, 

 the needle of the galvanoscope does not deflect, the clerk 

 knows that line 560 is occupied, having been connected 

 up by one of the other clerks, and instead of pushing 

 home the plug he pulls it out, and tells subscriber 85 to 

 wait, as line 560 is engaged. 



Long-distance telephony is admirably illustrated by 

 the opera at Munich being heard every evening with 

 marvellous clearness at the Frankfort Exhibition, some 

 200 miles away. 



The most striking feature of the Exhibition — indeed, 

 the exhibit that has brought many a foreigner hundreds 

 of miles to Frankfort — is the electrical transmission of 

 power from Lauffen, over a distance of 109 miles. No mea- 

 surements have yet been made by the jury of the exact 

 amount of power that is received, or of the efficiency of 

 the transmission ; but as over 1000 sixteen-candle lamps 

 are daily fed by the current, as well as an electro-motor 

 pumping up water to form a large artificial waterfall, the 

 actual power received must be something like 100 or no 

 horse. 



The plans had to be rapidly formed, for it was not until 

 May I that it was definitely decided to carry out the 

 experiment. The transformers have, on the one hand, been 

 duplicated, from an anxious dread on the part of each 

 firm of contractors that the other would not have finished 

 their work in time ; while, on the other hand, the insulators 

 of the proper size are yet only partly ready, and many are 

 defective from too hurried baking. Permission to carry 

 the wires had to be obtained from the four Governments 

 of Baden, Hesse, Wiirtemburg, and Prussia, and every 

 step of construction had to be taken under the depressing 

 influence of cavilling criticism. But in spite of all these 

 difficulties, it has been conclusively proved that, by 

 means of three overhead bare copper wires, each only 

 o"i58 inch in thickness, supported on poles such as are 

 used for ordinary telegraph lines, it is possible to deliver 

 some no horse-power at a distance of nearly no miles 

 from the water stream where the power is produced ; and 

 further, that this may be done without excessive loss by 

 actually maintaining a potential difference of some 18,000 

 volts between each pair of wires. 



The result is of international importance. The methods 

 that have been employed (and which will be fully 

 described) will probably not be copied in detail on a 

 future occasion ; there are doubtless faults which the 

 cautious engineer can criticize ; but the broad fact still 

 stands out prominently, that, by an experiment as bold 

 in conception as it has been successful in its realization, 

 the Allgemeine Electricitiits Gesellschaft of Berlin, in 

 conjunction with the Oerlikon Works of Zurich, have 

 made the thoughtful realize that towns like Milan, which 

 are within 30, 40, or 50 miles of vast water-power, may 

 become the industrial centres of the future. It is, indeed, 

 as if it had been shown that such towns stood on an 

 inexhaustible field of smokeless, dustless coal. 



{To be continued^ 



