If such a journey to the moon as the one described two chapters back were indeed possible, the voyage aloft would hardly be so easily and safely performed as is there taken for granted. Putting aside the thought of other difficulties, such as lack of conveyance and lack of air, there would be the danger of passing through a very considerable storm of missiles--a kind of “celestial cannonade”--which, to say the least, would prove very far from agreeable. These “starlets” and “meteor planets,” as they have been called, are not visible in a normal condition, because of their minuteness. But on entering our atmosphere they are rendered luminous, owing to the heat evolved by the sudden and violent compression of the air in front of the moving body. According to this view, shooting-stars, which simply dart across the heavens, may be regarded as coming within the limits of the atmosphere, and carried out of it again, by their immense velocity, passing on in space. Meteoric showers may result from an encounter with a group of these bodies, while aërolites are those which come so far within the sphere of the earth’s attraction as to fall to its surface. More than two thousand years ago the Greeks venerated a famous stone which fell from the heavens on the river Ægos. [Illustration: METEOR EMERGING FROM BEHIND A CLOUD (NOV. 23, 1877).] It will scarcely be believed what numbers of these shooting-stars or meteorites constantly fall to the earth. As she travels on her orbit, hurrying along at the rate of nineteen miles each second, she meets them by tens of thousands. They too, like the earth, are journeying round the great center of our family. But they are so tiny, and the earth by comparison is so immense, that her strong attraction overpowers one after another, drags it from its pathway, and draws it to herself. And then it falls, flashing like a bright star across the sky, and the little meteorite has come to his end. His myriads of companions, hastening still along their heavenly track--for the meteorites seem to travel commonly in vast flocks or companies--might, had they sense, mourn in vain for the lost members of their family. Any one taking the trouble to watch carefully some portion of the sky after dark, may expect to see each hour about four to eight of these shooting-stars--except in the months of August and November, when the number is much larger. About six in an hour does not sound a great deal. But that merely means that there have been six in one direction, and near enough for you to see. Somebody else, watching, may have seen six in another direction; and somebody else, a few miles away, may have seen six more. It is calculated that, in the course of every twenty-four hours, about four hundred millions of meteorites fall to earth, including those visible only through telescopes.