Since electricity has been recognized as the agent in the phenomena of thunder storms, inquiry as to whether it is a cause or a result of the formation of clouds, has produced evidence in favor of the latter fact (though clouds differently charged have mutual attraction for each other), for rapid motion of gases may be made to generate electricity. A natural sequence would be that thunder storms are most violent where clouds are heaviest. Hence, thunder storms are naturally most frequent and violent in the tropics, where the greater heat produces immense masses of vapor. and are unknown in the polar world, where the comparative dryness of the atmosphere is unfavorable. The unusual amount of electricity in dense clouds in rapid motion is shown by the tremendous electrical displays attendant upon tornadoes and cyclones. Another illustration of lightning resulting from cloud agency, rather than controlling them, may be found in the cloudless Sahara, where evidences of electricity are sometimes to be observed in the time of the Khamsin, while the thunder storm is unknown. One notable exception to the rule that thunder storms are violent and frequent in all tropical regions is to be found in Peru, with its cloudless skies and eternal sun, where a rainfall or a thunder storm would be as great a curiosity as a palm tree at the north pole. The mere fact of elevation renders the thunder storm more violent in mountainous regions, in both temperate and tropical worlds. Knowing the character of this mysterious power, we may not enter upon a lengthy discussion of the changes, chemical, physical and otherwise, that may be produced by it. Within the scope of this work, only its rank as an agent of destruction and a historical factor may be considered. Is electricity to be greatly feared? to be put on a par with the flood, the hurricane, and the earthquake? Has it ever figured in the history of nations sufficiently to directly affect their destinies? The first and most familiar aspect of its power is the thunder storm, which needs not a word of description. It results merely from the discharges passing between two bodies oppositely charged. There is one comparatively rare form of lightning, in which it appears as a globe of fire slowly descending, with wayward and unexpected dashes to the side, sometimes coming down a chimney and playing about the floor like a kitten, much to the discomfiture of the inmates, till it at length explodes with immense force, hurling zig-zag lightnings all about. This peculiar freak, several times observed, is as yet unexplained.