Page:The evolution of worlds - Lowell.djvu/63

Rh themselves may be moving before the encounter. Suppose, in the first place, that they were travelling in every possible direction, with the average velocity of the most erratic members of the family, the great comets. On this supposition calculation shows that we ought to meet 5.8 times as many at six in the morning as at six at night. If their orbits were smaller than this, say, something like those of the asteroids, we should find 7.6 to 1 for the ratio.

Suppose, however, that they were all travelling in the same sense as the Earth, direct as it is called in contradistinction to retrograde, and let us calculate what proportion in that case we should meet at the two hours respectively. It turns out to be 2.4 to 1 for the parabolic ones, 3.3 to 1 for the smaller orbited, or almost precisely what observation shows to be the case.$1$ Here, then, a bit of abstract reasoning has apprized us of a most interesting family fact; to wit, that the great majority of shooting-stars are travelling in the same orderly sense as ourselves. Furthermore, as some must be moving in smaller orbits than the mean, others must be journeying in greater; or, in other words, shooting-stars are scattered throughout the system. In short, these little bodies are tiny planets themselves, as truly planets as the asteroids,—asteroids of a general instead of a localized habit.