3. There was absolutely no doubt that on the same day many stones fell in the neighbourhood of L'Aigle.
Biot estimated the number of the stones at two or three thousand; they fell within an ellipse of which the larger axis was 6·2 miles, and the smaller 2·5 miles; and this inequality might indicate not a single explosion but a series of them. With the exception of a few little clouds of ordinary character, the sky was quite clear.
The exhaustive report of Biot, and the completeness of his proofs, compelled the whole of the scientific world to recognise the fall of stones on the earth from outer space as an undoubted fact.
The times and places of fall are independent of terrestrial circumstances.
15. Since that date many falls have been observed, and the attendant phenomena have been carefully investigated. These observations teach us that meteorites, as they are now called, fall at all times of the day and night, and at all seasons of the year, while they favour no particular latitudes: also they are found to be quite independent of the weather, and in many cases have fallen when the sky has been perfectly clear; even where stones have fallen in what has been called a thunder-storm, we may reasonably suppose that in most cases the luminous phenomenon has been mistaken for a variety of lightning, and the loud noise for thunder.
Velocity of meteorites.
16. From observations of the path and the time of flight of the luminous meteor, it is calculated that meteorites enter the earth's atmosphere with absolute velocities ranging from 10 to 45 miles a second: the velocity actually observed is that relative to a person at rest on the earth's surface; for the determination of the absolute velocity of the meteorite, the motion of the observer with the earth (about 18 miles a second) must be allowed for. Let us attempt to follow the course of a small compact body moving at such a rate. So long as the body is traversing "empty space," the only heat it receives is that sent direct from the sun and stars; in general, the meteorite will thus be probably very cold, and, owing to its small size and want of luminosity, it will be invisible to an observer on the earth's surface. After the meteorite enters the earth's atmosphere a very speedy change must take place. The resistance of the air. Assuming the law of resistance of the air for a planetary velocity to be the same as that deduced from experiments with artillery, the astronomer Schiaparelli[11] has shown that if a ball of 8 inches diameter and 32-1/3 lbs. weight enter the atmosphere with a velocity of 44¾ miles a second, its velocity on arriving at a point where the barometric pressure is still only 1/760th of that at the earth's surface will have been already reduced to 3-1/6 miles a second. From this it is clear that the speed of the meteorite after the whole of the atmosphere has been traversed will be extremely small, and comparable with that of an ordinary falling body. From experiments made by Professor A. S. Herschel, it has been calculated that the velocity of the meteorite which fell at Middlesbrough, in Yorkshire, on March 14, 1881, was, on striking the ground, only 412 feet a second. From the depth of the hole (20 to 24 inches) made in stiff loam by the stone which fell at Hvittis, in Finland, on October 21, 1901, it has been estimated by Mr. Borgström that the meteorite had a velocity of 584 feet a second when it reached the earth. He further calculates that the stone would have acquired virtually the same velocity if it had been merely allowed to fall, from a position of rest, under the action of gravity, through an infinite atmosphere having the same density as at the earth's surface. In the case of the Hessle fall, several stones fell on the ice, which was only a few inches thick, and rebounded without either breaking the ice or being broken themselves.
Transformation of the energy.
17. Further, Schiaparelli pointed out that, in the case imagined by him, the energy already converted into heat would be sufficient to raise 198,400 pounds of water from freezing point to boiling point under the ordinary barometric pressure. The greater part of this heat is, no doubt, carried off by the air through which the meteorite passes; but still the wonder is, not that a meteorite is small on reaching the earth's surface, but that any of it is left to "tell the tale."