Tyndall, John, 1820-1893 · New York, D. Appleton · leaf 112
string which passes over the grooved edge of the wheel,keeps the wire gently stretched. The wheel is accompaniedin its motions by the index, i, which is simply a long,light straw. If the wire be tightened, the index moves inone direction; if it be relaxed, the index moves in theopposite direction.… … for a moment with this free wire, the battery currentpasses through the platinum wire; it is heated, and its ex-pansion is instantly declared by the fall of the index. Onbreaking the circuit the wire cools, contracts, and theindex returns to its first position. A momentary touchagain brings the…
Heat
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