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The primary electrical property of a telegraph circuit on land is resistance. The artificial line for such a circuit is a simple "resistance box."
Artificial line for land line, late 1800s National Museum of American History, from Western Union |
Some operations - such as sending two messages on the same wire at the same time in opposite directions - need the help of an "artificial line." This is a set of components that duplicates the electrical properties of the telegraph circuit. Compare the artificial lines for overland and underwater circuits. You can see at a glance the complexity of the underwater circuit.
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The primary electrical property of a telegraph circuit on land is resistance. The artificial line for such a circuit is a simple "resistance box."
Artificial line for land line, late 1800s National Museum of American History, from Western Union |
| An underwater circuit combines resistance and capacitance (and sometimes inductance). You need a careful arrangement of components to mimic its electrical properties. The icebox-like insulated cabinet kept the equipment at a constant temperature. Note the improvised changes. Every time the real cable was repaired, its electrical properties changed, and the artificial line had to be adjusted to match. | |
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Components from artificial line for underwater cable, 1928
National Museum of American History |
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| Explore Resistance and Capacitance | |
| Resistance | |
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| Capacitance |  |
