19th century illustration of the phenomenon known as St. Elmo's Fire, from "Naturwunder Im Reiche der Luft" by Dr. W.F.M. Zimmerman, ca. 1860. First identified as an electrical phenomenon by Benjamin Franklin in 1749, St. Elmo's fire is a bluish-white plasma caused by the release of electrons in a strong electric field (200 or more volts per cm); the electrons have enough energy to ionize atoms in the air and cause them to glow. The phenomenon appears near pointed objects because electrical fields generated by charged surfaces are strongest where curves are sharpest. It is named after St. Elmo, the patron saint of mariners, as the phenomenon was often observed by sailors during thunderstorms at sea.