140 THE NATIONAL SCIENTIFIC INSTITUTIONS AT BERLIN. 



apparatus, and fifty-one apparatus of a peculiar construction. Two 

 hundred and eighty-two wires center at Berlin ; of these fifty-six are 

 underground and serve the larger circuit, thirty-seven, seventy, and 

 twenty-eight overhead wires are used for foreign, the larger and smaller 

 domestic circuits, respectively, while fifty-six underground wires accom- 

 modate the city trade. Within the city limits all wires, with the ex 

 ception of those used in telephoning, are placed underground. 



One hundred and twenty-four batteries, representing 7,350 elements, 

 together with eight batteries for special purposes representing 290 ele- 

 ments, are employed in the central office. 



Tlje Berlin service comprises 351.8 kilometers (218.G miles) of lines, 

 with 2,428.5 kilometers (1,509 miles) of wire; the ])neumatic service 

 comprises 40.5 kilometers '25 miles' of lines, with 40.3 kilometers (29 

 miles) of tubes. 



The i)neumatic line commences at the Central Telegrap.i Bureau, 

 radiates in six principal directions, and together with the branch lines 

 forms connection with thirty-three pneu matic offices. Each line runs one 

 train every fifteen minutes in either direction, with a velocity of 1,000 

 meters (3281 feet) per minute. The pressure and vacuum are produced 

 at eight stations, each of which is provided with a double set of en- 

 gines of a total force of 133 horse-power. Forty-four comi)artments of a 

 total capacity of 772 cubic meters serve to hold the compressed air and 

 the air ejected by the tubes. Each line controls a special series of sig- 

 nals. 



The telephone service was established in 1881. At the beginning 

 two central offices were established. Each of these received two switch- 

 boards for fifty plugs each. The great advantages of immediate personal 

 communication and the extraordinary simplicity of the arrangement 

 became so ai)parent that this mode of communication soon came into 

 general use. The increase is best illustrated by stating that from the 

 end of November, 1881, to June, 1886, the number of participants had 

 increased from 442 to 5,104, while the line had increased from 1,319 

 to 10,477 kilometers (819 to 6,510 miles.) 



In order to enable the subscribers to communicate with their own 

 homes or places of business from more distant i^arts and also to throw 

 the service open to general utility, public stations" were established 

 which could be used by any one so desirous upon the payment of a small 

 fee. At present there are twelve such stations. 



The constant increase in the number of telephones rendered it desira- 

 ble to extend the telephonic service beyond the city limits. The prog- 

 ress made in this field of technic, especially in the construction of long- 

 distance microphones, rendered it practicable to establish, in November, 

 1882, connection between Berlin and Charlottenburg ; in May, 1883, it 

 was extended to Berlin and Potsdam ; in December 1883 connection was 

 made between the exchanges of Berlin and Magdeburg ; in the years 

 1884 and 1885 with the surburban places: Westend, Kopenick, Steg- 



