2j6 
THE 1ELEGRAPH 
contact with s', and thence to the line through the binding 
screw 3 ; at the same time a negative current passes through s, 
along L to the stud q , and by the switch s" to the earth screw 
7. The relay is not affected, for the stud p which is connected 
with 4 and the other end of the relay is out of circuit, when the 
commutator s is turned to “ Send.” 
When the key is not pressed down, the levers L and l' rest 
on s” and s'”, then a negative current passes from the spring 
Fig. 169. 
s'” to the lever l', then by the stud o to the switch s', and thence 
through 3 to the line $ at the same time a positive current 
goes from s” through the lever L to the switch s", and by 7 to 
earth. The line is therefore always charged with a positive 
or negative current whether the key be depressed or not. 
When the commutator s is turned to “ Receive,” the battery 
is divided ; the line current enters at 3, the switch s' having 
- been put against the stud p, the current passes to the screw 4, 
traverses the relay and passes to earth. When the commutator 
is at “ Send,” the receiving apparatus is put out of the line 
