This phenomenon may occur by day as well as by night. It is often accompanied by one or several explosions, the report of which is sometimes perceptible to a considerable distance, and by a shower of meteorites. The globe of fire bursts, and splits up into luminous fragments, scattered in all directions. The different parts of the fire-ball fall to the surface of the Earth, under the name of aerolites, or rather of uranoliths, since they arrive from the depths of space, and not from our atmosphere. From the most ancient times we hear of showers of uranoliths to which popular superstitions were attached; and the Greeks even gave the name of _Sideros_ to iron, the first iron used having been sidereal. [Illustration: FIG. 56.--Fire-Ball seen from the Observatory at Juvisy, August 10, 1899.] [Illustration: FIG. 57.--Explosion of a Fire-Ball above Madrid, February 10, 1896.] No year passes without the announcement of several showers of uranoliths, and the phenomenon sometimes causes great alarm to those who witness it. One of the most remarkable explosions is that which occurred above Madrid, February 10, 1896, a fragment from which, sent me by M. Arcimis, Director of the Meteorological Institute, fell immediately in front of the National Museum (Fig. 57). The phenomenon occurred at 9.30 A.M., in brilliant sunshine. The flash of the explosion was so dazzling that it even illuminated the interior of the houses; an alarming clap of thunder was heard seventy seconds after, and it was believed that an explosion of dynamite had occurred. The fire-ball burst at a height of fourteen miles, and was seen as far as 435 miles from Madrid! In one of Raphael's finest pictures (_The Madonna of Foligno_) a fire-ball may be seen beneath a rainbow (Fig. 58), the painter wishing to preserve the remembrance of it, as it fell near Milan, on September 4, 1511. This picture dates from 1512. The dimensions of these meteorites vary considerably; they are of all sizes, from the impalpable dust that floats in the air, to the enormous blocks exposed in the Museum of Natural History in Paris. Many of them weigh several million pounds. That represented below fell in Mexico during the shower of meteors of November 27, 1885. It weighed about four pounds. [Illustration: FIG. 58.--Raphael's Fire-Ball (_The Madonna of Foligno_).]