HISTORY AND PROGRESS. 35 



Messages were sent with this apparatus at the rate of 

 ninety-two words in a quarter of an hour,* or over six words 

 per minute. 



The line wires were in three parts ; the first included a 

 length of 30,500 feet, erected in the air a few inches over the 

 roofs of the houses between the Royal Academy of Munich and 

 the Observatory at Bogenhausen. The weight of this section 

 was about 200 Ibs. The greatest span between two poles 

 was 400 yards. The second section of the line connected the 

 residence of Professor Steinheil with the Observatory in the 

 Lerchenstrasse, there and back a length of 2,000 yards ; 

 and the third section, a length of about 400 yards, connected 

 the Academy with the workshop of the physical cabinet. 



36. When experimenting on the Nuernburg and Fuerther 

 Railway, to ascertain if the rails could not be made use of 

 as lines for the service of a telegraph, Steinheil made the 

 important discovery that the earth might be used as part of 

 the circuit of an electric current. This discovery, which 

 ranks with those of Yolta and Oersted, was one of the greatest 

 contributions ever made to the progress of the telegraph. 

 Had the identity of the electricities been known earlier, 

 return circuits other than the earth for voltaic currents would 

 never have been used ; for in all the earlier experiments and 

 attempts with frictional electricity, the earth was used as the 

 return circuit. 



Steinheil took advantage of his discovery, and removed the 

 halves of his lines, leading, in their stead, the corresponding 

 connections of his apparatus to plates of metal buried in the 

 earth. 



A communicator of peculiar construction enabled the 

 operator to transmit to, and receive from, either Bogen- 

 hausen or Lerchenstrasse, at pleasure. It was arranged that 

 when the indicator was in circuit with one station, the wire 

 of the other should be connected to the multiplier of the 

 receiving instrument. 



The receiving instrument was not used exclusively to record 

 the messages on the paper strips ; sometimes small hammers 



* Dingier' s Journal, 67, p. 370. 

 D2 



