The most familiar type is the lightning we see in stormy weather; it flashes in brilliant zigzags from zenith to horizon, darts from cloud to cloud, or strikes like a javelin toward earth. At night, particularly in the country where no city lights mask its brilliance, lightning can be a frightening elemental force. A form popularly called “heat” or “sheet” lightning is a familiar, almost playful phenomenon in the midwest and southwest, although comparatively rare on the east coast. In hot, humid weather it flares intermittently near the horizon, noiseless because the luminous “sheets” are merely reflections of an ordinary zigzag flash that is too far away to be heard. “Bead lightning” has also been reported, appearing as a chain of spheroids that gradually fade away as they discharge. A spectacular display of “pinched lightning,” an even rarer phenomenon (see Plate Va), was photographed in late August 1961 at Los Alamos, New Mexico, during a severe thunderstorm[IX-7]. Ball lightning, which seems to be commoner in Europe than in North America (just as tornadoes are commoner in North America than in Europe) is so little understood that some scientists have doubted its reality. In recent years, laboratory research has added much to our knowledge of ball lightning and Soviet scientists in particular have studied it as a possible weapon against enemy planes[IX-8]. Ball lightning is usually described as a luminous ball whose diameter ranges from a few inches to several feet; the color may be red to orange or blue to white. These lightning balls appear most frequently toward the end of an electrical storm when the air is highly ionized, often just after a nearby lightning flash. They look and act like solid objects. They can hang motionless or drift in the air, glide along telephone wires or fences, roll down chimneys and across the floor to radio or TV sets, float a few inches above the ground or high in the sky. The ball persists as an entity for a time ranging from several seconds to many minutes; it may then evaporate noiselessly, or may disappear with an explosive noise and a force that can damage nearby objects[IX-8a]. One of the few existing photographs of ball lightning was taken at Lincoln, Nebraska, on August 30, 1930 (see Plate Vb). American, European, and Soviet scientists have suggested various theories, none of them entirely satisfactory, to explain the formation of ball lightning[IX-9, IX-10, IX-11]. These evanescent fiery globes probably represent some sort of continuous electric current perhaps held together by its own magnetic field, like the fabled hoop snake that could roll along the ground by holding its tail in its mouth.