Electric Wire Insulator
An insulator is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, as insulation. The term is also used to refer to insulating supports that attach electric power transmission wires to utility poles. Some materials such as glass, paper, or Teflon are very good electrical insulators.
Government Printing Office The Official Gazette of the United States Patent Office (Washington, DC: Government Printing Office, 1895)
Courtesy the private collection of Roy Winkelman