HISTORY AND PROGRESS. 117 



The anvils c and c" are in permanent connection with 

 the terminal c of the battery, and 2 and z" with the 

 terminal z. The spring s being down whilst the lever rests 

 on c' and z 1 , therefore the current from z goes through 2', 

 spring, plate p' t spiral of wire, to E, and thence to earth ; the 

 current from the c-pole goes from c, through c, plate p, the 

 connection wire, from this to the contact with the spring s, 

 terminal L, line, opposite station apparatus, to earth, &c. 

 The finger being still kept upon the button, when the lever 

 is pressed down the contacts c and z are broken, and c" and 

 z 1 ' made with the plates p and p. The current from 2' now 

 goes through z, s", plate p, connecting- wire, to E, spring s, L, 

 line, &c.; whilst the current from c goes through c, c", 

 plate p, spiral, E, earth, &c. Thus by keeping the button 

 pressed down and manipulating the key, reversed currents 

 are sent into the line. 



76. Varley's Switch for Submarine Work. This arrange- 

 ment, used on the Electric and International Company's 

 submarine line between England and Amsterdam, is for 

 sending a reverse current into the line when a usual signal 

 has been given by the key, and at the same time for keeping 

 the relay out of circuit so long as to insure it against the 

 injurious effects of the return currents. 



This is done by means of an extra relay, or electro- 

 magnetic switch. 



When the key is depressed at the transmitting station, 

 a positive current passes directly into the line, and a second 

 circuit is closed, which includes the electro-magnetic switch, 

 the attraction of whose armature breaks the relay circuit, 

 but completes the circuit by which a reverse current is sent 

 into the line as soon as the key is let go again. 



The key used in this arrangement is shown in Fig. 63. 

 The customary working and reposing contacts are represented 

 by a and d ; c is the bearing of, and in contact with, the lever. 

 A third contact is brought on in front at a', which is touched 

 by the spring r, attached to the terminal b, when the spring is 

 pressed down. F is, of course, pressed down by an insulated 



