CHAP, in.] ELECTRIC TELEGRAPHY. 561 



sometimes further from the centre, performing in this way as many 

 oscillations as the handle passes over successive divisions on the 

 dial. 



We now see how the motion given to the handle of the manipu- 

 lator produces a series of completions and interruptions of the current 

 in the line wire. We must next describe the different pieces of the 

 manipulator and the communications they make between the batteries, 

 the line wires, and the apparatus them'selves. 



The wire which comes from the positive pole of the battery reaches 

 the end R, which is connected by a metal band to the screw p. Oppo- 

 site the point of this screw is that of another, Q, which is connected 

 in the same way with the end R' to which is attached the wire 

 of the indicator. Between the points of these screws the oscillation 

 of the branch of the lever T takes place, which touches first one and 

 then the other. Suppose the manipulator at rest, or the handle at the 

 cross, which is the position indicated in Fig. 360. In this case, the 

 current does not pass, for the circuit is not closed, and the same is the 

 case whenever the lever has the same position, that is to say each time 

 that the handle passes over an even division, as B, D, F, or the figures 

 2, 4, 6. If, on the contrary, the needle in moving passes over to an 

 odd division, or stops there, the current enters by the lever T to the 

 movable wheel of the manipulator. It remains to shew how it is sent 

 through one or other of the line wires, to the right or the left of the 

 station. It is in L and L' that these wires end. The two metal tongues 

 L and "if are in permanent connection with two spring cornmu-, 

 tators r r ', which may be turned by means of a handle, and whose 

 springs connect them at will either with the tongues sm s'm' or with 

 ends of the metal band CD. 



If it is required to communicate with the telegraphic station to 

 the left, the spring of the commutator r must be placed upon m; to 

 correspond with the right, the spring / must be placed on m. The 

 two pieces m and m' are in metallic connection with the movable 

 wheel of the manipulator. Then if a current from the battery arrives 

 in this wheel it passes through m, the spring r, the attachment L and the 

 wire to the left as stated. The current sent along the line arrives at 

 the indicator of the receiving station, then through the earth wire of 

 that station, and returns by the earth itself to the negative pole of the 

 sending station. The same process takes place in the line to the right 



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