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 a while. It occurs naturally but rarely, but 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."
(Source: PhysicsWeb, Scientific American)