1904: Physicist Nikola Tesla attempts to explain the phenomenon of "ball lightning."

Ball lightning (if it exists at all) is an electrical discharge, usually appearing in spherical shape that, unlike regular lightning, tends to linger awhile. It occurs naturally but rarely, and despite the best efforts of Tesla and others, the exact origin of the phenomenon remains a mystery.

Although reported sightings are most common during storms and other unsettled weather, ball lighting has been observed during periods of absolute calm. It has also been spotted in some pretty screwy places: hovering over a kitchen stove, following a car down a street and, most famously, flying alongside aircraft during World War II. Allied pilots, mistaking the glowing spheres for the lights of enemy aircraft, referred to them as "foo fighters."

"I never saw fire balls," Tesla wrote in Electrical World and Engineer on March 5, 1904, "but as compensation for my disappointment I succeeded later in determining the mode of their formation and producing them artificially," He regarded ball lightning as a manifestation of a larger phenomenon: "[T]his planet, with all its appalling immensity, is to electric currents virtually no more than a small metal ball."

Tesla hoped to use this phenomenon to transmit through the air not only telegraph and voice signals, but electrical power itself. Contemporary reports say Tesla used a generating apparatus to create electrical balls about 1½ inches in diameter and played with them to wow onlookers.

Tesla is perhaps better known for his pioneering work on alternating current as the basis for an electrical-distribution grid. George Westinghouse bought Tesla's patents, and AC power eventually triumphed over Thomas Edison's competing direct-current system.

Source: PhysicsWeb, Scientific American

Image: Tesla sits in his lab in Colorado Springs, Colorado, circa 1900.

An earlier version of this article appeared on Wired.com March 5, 2007.