According to Arago’s investigations, the evolution of Lightning is of
three kinds: zigzag, and sharply defined at the edges; in sheets of
light, illuminating a whole cloud, which seems to open and reveal the
light within it; and in the form of fire-balls. The duration of the
first two kinds scarcely continues the thousandth part of a second; but
the globular lightning moves much more slowly, remaining visible for
several seconds.