HISTORY AND PROGRESS. 



107 



It is evident, therefore, that the currents arriving by L 1 

 and transmitted along L 2 , exactly correspond with each other, 

 and that, with regard to the battery c z, and the line L 2 , the 

 beam b of the apparatus in the figure replaces a common 

 transmitting key. 



Each station corresponding with two lines, however, is 

 almost invariably provided with two instruments, so that 

 correspondence in both directions may be carried on at the 

 same time. 



When this is the case, the two instruments are connected 

 up, as is shown in the plan Fig* 58, in which the necessary 



Fig. 58. 



commutators for altering the position of the apparatus for 

 other uses are left out. The currents arriving by L 1 on the 

 left, go across to the beam 1 of the Morse apparatus H 2 , on 

 the right, which remains passive, through contact, 2, to coils 

 of Morse H L on the left, earth, &c. Each movement of the 

 beam of the latter closes the circuit of the line-battery, c z, 

 with the line L 2 , through c, 3 (beam of Morse Hj), 1, L 2 , 

 opposite station apparatus, earth, back to z of battery. 



72. Varky's Translating Apparatus. A highly ingenious 

 arrangement has been invented by Mr. C. Yarley, formerly 

 engineer to the Electric and International Telegraph Com- 

 pany, and is used on the company's lines. 



