"As a physical philosopher be has no superior in our country [at least] among the young men."
Geologist Benjamen Silliman on Joseph Henry
When American Joseph Henry (1797-1878) first became interested in science at the age of sixteen, he found electricity fascinating and began experimenting with electromagnets.
Wires carrying electricity produce weak magnetic fields around them. If, however, the wire is coiled many times around a metal such as iron, the effect is magnified and the resulting magnetic field is much stronger. The first electromagnets were coiled very loosely to prevent the current-carrying wires touching and causing an electrical short circuit. Henry was the first to use an insulating cover for the wires so that they could be wrapped more tightly and in many layers, multiplying the effect. Henry's first insulation for wires
was tediously made from strips of his wife's petticoats.
The material of the insulator has to resist the flow of electricity. This is done by ensuring that the constituent atoms have tightly bound electrons. The first transatlantic telegraph cables were insulated using gutta-percha, a latex sap from a species of tropical tree. This unfortunately deteriorated when exposed to air, so early power cables were wrapped in jute and placed inside bitumen-filled pipes. By the late 1890s wire insulators made of rubber or oil- impregnated paper became common. By World War II insulation made of synthetic rubber and polyethylene was being introduced.
