it would be in the highest degree improbable that any of these objects should now be from time to time descending to the earth. For suppose that a meteorite is shot away from the moon, it presently comes so completely under the attraction of the earth that it must revolve about it in accordance with the laws imposed by the earth's gravitation. The question, therefore, as to whether it is to fall on the earth or not, is simply decided by whether the distance of the little body when at perigee would be less than the radius of the earth. If this were so, then of course the body would strike the earth at its first revolution. If, however, the circumstances under which the body was projected were such that its movement did not bring it into collision with the earth at the first approach, then it would remain as a permanent satellite to our globe. It could never then fall to the earth except under the possible action of such disturbing forces as are generated by the attraction of the sun or the moon. No doubt it is conceivable that under the influence of these disturbing forces it might happen, in extremely rare instances, that a missile, after wandering for ages round the earth in an elliptic orbit, should at last be so deflected from its original path as to strike against the earth's surface. But a little attention will show that such an occurrence must be of a rarity so extraordinary, that it may be dismissed from consideration as the probable source of meteorites, at all events when a more rational explanation is at hand.
The question as to the lunar origin of meteorites has thus become narrowed down to a simple issue. Are there at present any active volcanoes on our satellite? If there are, then it might be quite conceivable that
