HISTORY AND PROGRESS. 119 



be raised very quickly, allowing the weight to drop and the 

 cord to run over the axis ; but it cannot be lowered without 

 first turning the wheel, pinion, and fly, and raising the 

 weight, an operation occupying about half- a- second. 



The purpose of this is that the armature may be attracted 

 suddenly to the poles of the electro- magnet when a signal is 

 given, but that on being released the beam shall take some 

 time to return to its position of rest, and that during the 

 greater part of this time the spring /shall remain in contact 

 with the screw w in connection with the reverse battery. 



A plan of the station arrangements at London on the line 

 working to Amsterdam is shown in Fig. 65. 



When transmitting or receiving, contact-pegs are put 

 into the holes 1 and 2 of the commutator c. On giving a 

 signal by pressing down the key, contacts between a and c 

 by the beam, and between a and b by the spring moved by 

 the lever before mentioned, are established. By means of 

 the former, the circuit of the copper battery is closed (c, a, e, 

 m, commutator 1, IT, G, line), and by means of the latter 

 that of the switch (b, coils of switch, z, switch battery, c, a, 

 spring of key). The beam of the switch is in permanent 

 connection with the reposing contact d of the key, and by 

 oscillating puts on one side the relay, on the other the zinc- 

 pole, of the battery into circuit. 



When the switch is at rest the relay is in circuit with the 

 reposing contact of the key, (line, G, n, comm. 1, in, key, e, 

 d, iv, switch-beam, u, v,. coils of relay, earth) ; but as the 

 return currents would take this way when the key is lifted 

 up, the contact u is interrupted by the attraction of the 

 armature. At the same time the contact w with/ is made, 

 and this advances z of the zinc-battery (z, switch, w,f, iv, 

 d) to the back contact of the key, so that the moment the 

 key is let go the circuit of the zinc-battery may be completed 

 (key, d, c, m, comm. 1, n, G) with the line. 



If this takes place at London the positive currents will 

 arrive at Amsterdam by cable, commutator, key, switch, coils 

 of relay, earth. The tongue of the relay at the Amsterdam 

 station will be deflected against the contact-point and close the 



