“This, indeed, is the maximum and, I should add, a number altogether inconceivable; but, gentlemen, let us take the minimum, if it be your pleasure, and let us admit that the impact is not direct, but more or less oblique, and that the mean velocity is not greater than 30,000 meters per second. Every kilogram of a bolide would develop in this case 107,946 heat units before its velocity would be destroyed by the resistance of the air; in other words, it would generate sufficient heat to raise the temperature of 1079 kilograms of water from 0° to 100°—that is, from the freezing to the boiling point. A uranolite weighing 2000 kilograms would thus, before reaching the earth, develop enough heat to raise the temperature of a column of air, whose cross-section is thirty square meters and whose height is equal to that of our atmosphere, 3000°, or, to raise from 0° to 30° a column whose cross-section is 3000 square meters. “These calculations, for the introduction of which I crave your pardon, are necessary to show that the immediate consequence of the collision will be the production of an enormous quantity of heat, and, therefore, a considerable rise in the temperature of the air. This is exactly what takes place on a small scale in the case of a single meteorite, which becomes melted and covered superficially by a thin layer of vitrified matter, resembling varnish. But its fall is so rapid that there is not sufficient time for it to become heated to the center; if broken, its interior is found to be absolutely cold. It is the surrounding air which has been heated. “One of the most curious results of the analysis which I have just had the honor to lay before you, is that the solid masses which, it is believed, have been seen by the telescope in the nucleus of the comet, will meet with such resistance in traversing our atmosphere that, except in rare instances, they will not reach the earth entire, but in small fragments. There will be a compression of the air in front of the bolide, a vacuum behind it, a superficial heating and incandescence of the moving body, a roar produced by the air rushing into the vacuum, the roll of thunder, explosions, the fall of the denser metallic portions and the evaporation of the remainder. A bolide of sulphur, of phosphorus, of tin or of zinc, would be consumed and dissipated long before reaching the lower strata of our atmosphere. As for the shooting stars, if, as seems probable, there is a veritable cloud of them, they will only produce the effect of a vast inverted display of fire-works. [Illustration: MAKING FOR THE ANTIPODES. ]