may, however, conclude that in its voyages through space the meteorite pursues a track which generally or frequently crosses the earth's track. This conclusion is a most essential point, and in it lies the fundamental argument in favour of the terrestrial origin of meteorites.
Have we not seen the improbability that a meteorite projected from a minor planet, such as Ceres, shall fulfil the necessary condition of crossing the earth's track, for there are so many chances against it? Have we not also seen that a meteorite projected from a globe lying in the stellar regions would almost certainly fail even to cross the orbit of our earth, inasmuch as the probability of its doing so would be only one against many thousands of millions? When, however, we locate the volcanoes which are presumed to be the origin of meteorites on the earth, these improbabilities disappear altogether. Instead of the chances against the orbits of these bodies crossing the earth's track being millions to one, or thousands to one, the fact that they must generally or frequently do so has become a demonstrable certainty. Indeed, they would always do so were it not possible in certain cases for the existence of disturbances, such as would be produced by the passage of a meteorite near the moon, to derange the path so far as to warp the little body into a direction which passed slightly within or slightly without the earth's track, instead of directly through it. There is also the effect of planetary perturbation both on the orbit of the meteorite and on that of the earth to be borne in mind. But the probabilities of the situation have been entirely transformed when we consider the terrestrial theory of meteorites. The probabilities are now that the missile does fulfil the necessary condition of crossing the earth's
