Ball lightning is an atmospheric phenomenon, the physical nature of which is still controversial. The term refers to reports of a luminous object which varies in size from golf ball to several meters in diameter. It is sometimes associated with thunderstorms, but unlike lightning flashes arcing between two points, which last a small fraction of a second, ball lightning reportedly lasts many seconds. There have been some reports of production of a similar phenomenon in the laboratory, but some question whether it is the same phenomenon.

Reports
One of the earliest and most destructive occurrences was reported to have taken place during The Great Thunderstorm at Widecombe-in-the-Moor, Devon, in England, on October 21, 1638. Four people died and around 60 were injured when what appeared to have been ball lightning struck a church.

Homemade experiments
Currently there is no widely accepted explanation of what exactly ball lightning is, despite several theories that have been advanced since the phenomenon was brought into the scientific realm by the French Academy scientist François Arago.
An early attempt to explain ball lightning was recorded by Nikola Tesla in 1904.
Singer in his monograph, The Nature of Ball Lightning, published by Plenum Press critiques several classes of theory. Most theory can match some of the reported properties of ball lightning but not all. In addition there are several difficulties that need to be overcome with many of the proposed theories.
Ball lightning theories are distinguished by having the energy either self-contained or with energy being supplied to the ball by an external source. In the latter case much longer life times are possible.
The types of theories vary widely. There are electrical discharge theories, spinning electric diplole theory, electro-static Leyden jar theories, nuclear theories, trapped microwave theories, fractal aerogel theories, magnetically-trapped plasma theories, vortex theories, metallic vapour theories, Rydberg matter theories, chemical combustion theories, black hole theories, antimatter theories, optical illusions (e.g. lightning after image on the retina theory etc).
Each of these theories is now described. These are the types of candidate theories but they need to be able to account for eyewitness accounts. No one theory has been widely accepted so there needs to be some debate within the scientific community as to the likely cause of ball lightning.

Spinning electric dipole theory. (Endean (1976) published this theory. He postulated that ball lightning could be described as an electric field vector spinning in the microwave frequency region.)
Electrostatic Leyden jar models. (Singer (1971) discusses this type of theory and suggested that the electrical recombination time would be too short for the ball lightning lifetimes often reported.)
Nuclear theories
Trapped microwave theories
Maser caviton theory
Fractal aerogel theories (Smirnov (1987) put forward a charged aerosol cluster theory.)
Magnetically trapped plasma theories
Vortex theories (Coleman (2006) described ball lightning as a vortex fireball or natural vortex burning a combustible fuel. Ball lightning under this theory is essentially a turbulent swirling flame inside a vortex.
Rydberg matter theories
Chemical combustion theories
Black hole theories
Anti-matter theories
Optical illusions. Analysis/Theories
Ball lightning has been connected to reports of several supernatural phenomena, ranging from will o' the wisps to UFOs. Some people believe the ball lightning phenomena are ghosts or spirits, or are related to poltergeists and spontaneous human combustion.

Esoteric explanations
Among the ancients of Japanese mythology, there is a myth that ball lightning is the wrath of the thunder god, Raijin from Japanese mythology. In Basque mythology ball lightning were believed to be either main deity, Mari or Sugaar, travelling from one mountain to another. M. l'abbé de Tressan in, Mythology compared with history: or, the fables of the ancients elucidated from historical records,
..during a storm which endangered the ship Argo, fires were seen to play round the heads of the Tyndarides, and the instant after the storm ceased. From that time, those fires which frequently appear on the surface of the ocean were called the fire of Castor and Pollux. When two were seen at the same time, it announced the return of calm, when only one, it was the presage of a dreadful storm. This species of fire is frequently seen by sailors, and is a species of ignis fatuus. (page 417)
Some phenomena known from folklore, such as the will o' the wisp, may be related to ball lightning.
An early fictional reference to ball lightning appears in a children's book set in the 1800s by Laura Ingalls Wilder.

See also

Barry, James Dale (1980). Ball Lightning and Bead Lightning. New York: Plenum Press. 
Cade, Cecil Maxwell; Delphine Davis (1969). The Taming of the Thunderbolts. New York: Abelard-Schuman Limited. 
Coleman, Peter F. (2004). Great Balls of Fire—A Unified Theory of Ball Lightning, UFOs, Tunguska and other Anomalous Lights. Christchurch, NZ: Fireshine Press. 
Coleman, P.F. 2006, J.Sci.Expl., Vol. 20, No.2, 215–238.
Endean, V.G.,1976, Nature, 263,753,754.
Golde, R. H. (1977). Lightning. Bristol: John Wright and Sons Limited. 
Golde, R. H. (1977). Lightning Volume 1 Physics of Lightning. Academic Press. 
Singer, Stanley (1971). The Nature of Ball Lightning. New York: Plenum Press. 
Smirnov, 1987, Physics Reports, (Review Section of Physical Letters,152, No. 4, 177–226.
Stenhoff, Mark (1999). Ball Lightning, An Unsolved Problem in Atmospheric Physics. New York, Boston, Dordrecht, London, Moscow: Kluwer Academic/Plenum Publishers. 
Uman, Martin A. (1984). Lightning. Dover Publications. 
Viemeister, Peter E. (1972). The Lightning Book. Cambridge: MIT Press.