100 THE ELECTRIC TELEGRAPH. 



through the galvanoscope inserted in the line circuit and 

 give notice to the operator. 



68. Borggreve's Commutator for Intermediate Stations. 

 The many inconveniences arising from delay in the reception 

 and transmission of messages, combined with the possibility 

 of mistakes in stoppering the holes of Nottebohm's commu- 

 tator for the different positions of the apparatus, has shown 

 the necessity of furnishing intermediate stations with two 

 apparatus. This enables them to correspond with the stations 

 on both sides at the same time. 



M. Borggreve, Inspector of Telegraphs in the Prussian 

 service, has arranged a commutator for the use of inter- 

 mediate stations with two apparatus, in which, as in that of 

 Siemens and Halske, only one stopper is required. It is 

 composed of five brass slabs screwed on an insulating base of 

 vulcanite. 



The way in which the commutator is connected with the 

 two Morse-apparatus, as well as its form and appointments, 

 is shown in the plan, Fig. 53. 



The line wires L 1 and L 2 are connected to the upper screws, 

 while the lower screws on the same bars are connected with 

 the levers of the transmitting keys K 1 , K 2 . To the binding- 

 screw of the middle bar is attached the earth-wire, and to 

 the screws of two intermediate bars, the cross-commutators 

 c 1 and c 2 , whose opposite points go to the back contacts of 

 the keys. R I and R 2 are the relays of the two Morse-appa- 

 ratus M 1 and M 2 . The two local circuits are supplied with a 

 common local battery, B, and the two line circuits with a 

 common line battery, L B. When the contact plug is inserted 

 in hole 1 of the commutator u the apparatus are both short- 

 circuited, and currents pass through L 1 , G 1 , stopper 1 of com- 

 mutator, G 2 , L 2 , &c. The employe sees by the deflections or 

 otherwise of his galvanoscope-needle when the direct corre- 

 spondence of the end or distant stations is concluded, usually 

 by an agreed signal. 



If the stopper is in hole 2, apparatus 1 can correspond 

 with the line L 1 , and apparatus 2 with the line L 2 , inde- 

 pendently of each other. The currents arriving by L 1 go 



