In the earliest the conductor was represented by long metal wires, supported by silk or other insulating material, and left to pick up the air's potential.
Thomson (Lord Kelvin) at a meeting of the Philosophical Society of Glasgow in 1854, because its greater flexibility renders it less likely to damage the insulating envelope during the manipulation of the cable.
17 and a thickness of insulating material which formerly would have been considered quite insufficient is now very generally adopted with complete success.
This surface is divided into two parallel halves by a short insulating space on which the arm normally rests, so that two separate conducting surfaces are provided, with either one of which the arm will make contact in its excursions in one direction or the other from the central position, the direction and duration of contact being governed by the motion of the suspended coil.
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