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Rh the Moon. That they are of domestic manufacture is, however, negatived by the paths they severally pursue. Nor can they for like reason have been ejected from the Sun.

The Earth was not their birthplace. It is alien ground in which they lie at last and from which we transfer them to glass cases in our museums. This fact about their parentage they tell by the speed with which they enter our air. They become visible 100 miles up and explode at from 20 to 10, and their speed has been found to be from 10 to 40 miles a second, which is that of cosmic bodies moving in large elliptic orbits about the Sun,—a speed greater than the Earth could ever have imparted.

Four classes of such small celestial bodies tenant space where the planets move: sporadic shooting-stars, meteorites, meteor-streams, and comets. The discovery of the relation of each of these to the solar system and then to each other forms one of the latest chapters of astronomic history. For they turn out to be generically one.

It was long, however, before this was perceived. The first step was taken simultaneously by Professor Olmstead of Yale and Twining in 1833 from reasoning on the superb November meteor-shower of that year. All the shooting-stars, "thick as snowflakes in a storm," had a common radiant from which they seemed to come. D