TELE GRAPHIC APPARATUS . 
213 
carries iho handle, is made of brass, in two parts, d and F, 
which are separated by insulating material : n is connected 
with the copper pole, and f with the zinc pole. Two steel 
springs, p p\ connected respectively with the pieces b b\ put jt? b 
into communication with A, that is to say, with the coils, and 
connect p' p' with 'b, i.e., with the earth. These two springs 
press strongly against the part I) and F, and thus the con¬ 
tinuity of the line is main¬ 
tained. The f half of the 
armor has a projection, m (fig. 
147), which rests between the 
two springs p and p without 
touching either of them so 
long as the handle is at rest. 
We know that b p and b ' p 
are in metallic contact. If 
now the handle is turned to 
the left, m follows the move¬ 
ment, and by pressing against 
b (which is in communication 
with A through p) connects 
the copper pole with the line; 
at the same instant the pro¬ 
jection m is turned to the 
right, and pressing on the 
spring p\ it puts 5', and there- - 
fore b and 0 into communica- 
tion; and thus carries the 
zinc current into earth. If 
now the handle is turned to 
the right, all the movements 
are reversed; the projection ml 
is brought into contact with b 
and therefore connects the copper with the earth ; whilst m 
pressing against p sends the zinc current into the line. The 
current may then be considered as passing through the earth 
to the coils of the distant station and deviating the needle 
there in the direction opposite to that in the former case, and 
then returning through the line wire to A, by which it reaches 
the zinc of the battery. 
Fra. 147. 
