"A shooting-star!" Frank exclaimed. "Or perhaps a meteor," Fred responded. "Either way you like," said the Doctor, "as both names are used for the phenomenon. It also has the name of 'falling-star,' as the path is generally downward, or apparently so." Frank asked what a shooting-star, meteor, or falling-star was composed of, and what was the reason of its appearance. "That is a question more easily asked than answered," the Doctor replied. "Scientific men in all parts of the world have devoted a great deal of time and attention to the subject, but they are not, as yet, satisfactorily informed as to the character of the meteor." "Don't they fall on the earth sometimes?" Fred inquired. "I have read of aerolites that came from the air to the earth, and were composed of solid matter. Are not these aerolites parts of shooting-stars?" "Circumstantial evidence favors the theory that some of the aerolites come from falling-stars; but, at the same time, no solid matter has reached the earth that can be directly traced to one. The amount of solid matter in an ordinary shooting-star is so small that it is thought to be consumed in its passage through the air, where its great velocity causes it to be heated to a very high degree; whenever anything has fallen from the sky to the earth, and been found at the time of its fall, it is always intensely hot." "How far off was that meteor we just saw?" said Frank. "Fifty or sixty miles, I presume," the Doctor answered. "It has been determined that shooting-stars begin to be visible at distances varying from forty to one hundred and twenty miles, and disappear at from thirty to eighty miles. During the time we saw it, it moved about ninety miles; it was in sight three or four seconds, and its velocity was, therefore, not far from thirty miles a second; a pretty fast rate of travelling." "Ever so much faster than a cannon-ball," Fred remarked. "No wonder it gets heated so that it is consumed." "But you didn't tell us about the aerolites, and what they are made of," Frank protested. "Nor about the circumstantial evidence in favor of their coming from the shooting-stars," added Fred. "Several instances may be given," Doctor Bronson replied; "but the following from Professor Loomis will be sufficient to illustrate the theory: "On the morning of December 14th, 1807, a meteor of great brilliancy was seen moving in the atmosphere over the town of Weston, in Connecticut. Its apparent diameter was about half that of the full-moon; when it disappeared several persons heard a sound resembling the discharge of a cannon, followed by smaller reports like a fire of musketry. Soon after the explosions a man heard a sound like the falling of a heavy body, and upon examination he discovered that a stone had fallen upon a rock near his house and was dashed into fragments, which were quite hot when picked up. When put together they were found to weigh about twenty pounds.