St. elmo's fire

From Glossary of Meteorology

St. Elmo's fire

(Also called Elmo's fire, corposant.) Corona or point discharges that occur when the environmental electric field is high, typically at the tips of sharp conductors that enhance the electric field.

This name was given the phenomenon by Mediterranean sailors who regarded it as a visitation of their patron saint, Elmo (Erasmus). Their superstition also led to the equivalent term corposant. An appearance of St. Elmo's fire was regarded as a good omen, for it tends to occur in those latter phases of a violent thunderstorm when most of the surface wind and wave disturbance is over.

Schonland, B. F. J. 1950. The Flight of Thunderbolts. 44–47.