HISTORY AND PROGRESS. 129 



terminal bar, F, connected to one side of the galvanoscope. 

 By supplying one or more of these holes with contact pegs, 

 the apparatus may be arranged in different positions. 



When the two apparatus, I. and II., are to work as ter- 

 minals to the two lines L X and L 2 respectively, contact pegs 

 are inserted in the holes s, and between and E, of each of 

 the boards. The circuit is then complete for receiving from 

 L!, through L, B X , F, s, 1 and 2 of D X , coils of H X , > E, earth ; 

 and for transmitting, when the key is pressed down, through 

 Earth, E, ^, z, Battery, c, ^, and 3 and 1 of T> L , s, F, B I? L, 

 LJ, &c. 



For translation between L X and L 2 , contact pegs are put in 

 the holes between T and F, and between ^ and E, of each of 

 the apparatus. The currents from L L then pass through L, B I? 

 F, T, i, to App. II., i , 1 and 2 of H 2 , n, back to App. L, 

 ii, Coils of H L , g, E, Earth, &c. The beam of H L is deflected, 

 and closes the circuit, including Earth, E, , z, Battery, c, 

 to App. II., n r , back to App. L, in, 3 and 1 of H 1? i, to 



App. II., T, F, B 2 , L, L 2 , &0. 



Both apparatus are intermediate when a contact peg is 

 inserted in the hole between s and F of each of the boards. 

 In this case both apparatus are moved by the same currents, 

 and record simultaneously. 



Either of the apparatus may be used alone as intermediate 

 or circular apparatus, when its contact peg is between s and 

 F, while the other apparatus has a peg in the hole between 

 D and F. 



Both apparatus are out of circuit when the pegs of both 

 are put in the holes , F. The through-circuit, L X , L, B X , F, 

 D, z, to App. II., z, p, F, B 2 , L, L 2 , is then established. 



The insertion of pegs in the holes between L and F of the 

 boards short-circuits the galvanoscopes, and between F and L 

 and F and E, at the same time, puts the lines directly to 

 earth a position always advisable during a thunderstorm. 



When the ink- writer is used with a relay, the arrange- 

 ments of the board undergo some modification. This consists 

 in the addition to each board of a relay, G (Fig. 71), and of 

 two terminals, c z, for the poles of a common local battery. 



K 



