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Siemens Pocket Line Sounder and Key for Open Circuit Telegraph Lines
1. Iron yoke and cores of Electromagnets
2. Wire coils encircling cores of Electromagnets
3. Iron armature controlled by spring
4. Key with front and back contacts, pivoted in centre of levers.
5. Front or battery contact.
6. Back or relay contact.
This instrument is portable and can be used at every point on a telegraph line, provided the user has a battery of sufficient power. D is the terminal for the Down Line and U for Up Line. The Earth may be used in place of either. The battery is connected to U and C. Suppose a message to be received on the instrument (which is read by sound). A current will enter at U, and passing through the coils 2, 2 will magnetise the cores and attract the armature (3). It then enters the Key at 6, along lever 4 and thence out at D. When the current is stopped the armature falls back: signals are formed according to the Morse Code by its motions. If the station is sending a message and his key is depressed the circuit is from U, which is the zinc pole of the battery, the battery to 5, through 4 to Down Line, to Earth at terminal station, through the Earth to the terminal station of the Up Line and back by Up Line to U. It will be noticed that when the battery is in use the Electromagnet Sounder is not and vice versa.