This was constructed of a shallow box placed in a vertical position, with metallic front and back and insulating sides.
In the Hospitalier ondograph, 1 a synchronous electric motor driven in step with the periodic current in the circuit being tested drives a cylinder of insulating material having a metallic slip let into its edge.
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.
Ebonite takes a fine polish, and is valuable to the electrician on account of its insulating properties, and to the chemist and photographer because vessels made of it are unaffected by most chemical reagents.
