We are all familiar with the appearance of the instrument maker's induction coil; its polished mahogany base, its lacquered brass fittings, and its secondary bobbin constructed of and covered with ebonite.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
These coils are, however, destitute of any iron core, and they generally consist of coils of wire wound on a fibre, wooden or ebonite frame, and must be immersed in a vat of oil to preserve the necessary insulation.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
ebonite has the further advantage on land that it takes but a single wire.
"A brief sketch of the work of Matthew Fontaine Maury during the war, 1861-1865"
Richard L. Maury