Lightning Arrester, Counter-electro-motive Force

An invention of Prof. Elihu Thompson. A lightning arrester in which the lightning discharge sets up a counter-electro-motive force opposed to its own. This it does by an induction coil. If a discharge to earth takes place it selects the primary of the coil as it has low self-induction. In its discharge it induces in the secondary a reverse electro-motive force which protects the line.