The vivid flash of light which accompanies a sudden discharge of atmospheric electricity. It occurs in three distinct forms - namely, forked lightning, sheet lightning, and ball-lightning. In forked lightning the path taken by the electricity is that which gives the least resistance, and is distinctly seen to be made up of straight lines and sudden bends. Sheet-lightning appears as a diffused glare of reddish color, spread over a considerable extent of the sky, and is sometimes called summer lightning, as it is of frequent occurrence in warm weather. Ball-lightning is a very destructive and dangerous form of lightning, but happily of rare occurrence.