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This arises from the concussion of the air compressed by the rapid flight.

In rare cases the mass is so large that it reaches the earth without being melted or evaporated. Then we have the fall of a meteoric stone, as it is called, which commonly occurs several times a year in some part or another of the world. There is at least one case on record in which a man was killed by the fall of such a body. When these stones are dug up they are found to be composed mostly of iron. Specimens of them are kept in our museums, where they may be examined by anyone who wishes to see them. Some remarkable ones are found at the Smithsonian Institution, Washington, D. C.

How these objects originated we cannot say, and even a guess on the subject would be hazardous. When found they bear marks on their surface of having been melted; this, however, is a natural result of their passage through the air, by which the surface is always heated far above the melting point.

The greatest discovery of our times on the subject of meteors is connected with the meteoric showers already referred to, which occur at certain seasons of the year. The most remarkable of these occur in November, and the meteors of the shower are called Leonides, because their lines of apparent motion all diverge from the constellation Leo. It was found by historical research on the subject that this shower had recurred at intervals of about one third of a century for at least thirteen hundred