8. It has already been supposed, by many astronomers, that shooting stars, and meteoric stones, are bodies of connected nature and origin; and that they are cosmical, not terrestrial bodies;--parts of the solar system, not merely appendages to the earth. It has been conceived, that the luminous masses, which appear as shooting stars, when they are without the sphere of terrestrial influences, may, when they reach our atmosphere, collapse into such solid lumps as have from time to time fallen upon the earth's surface: many of them, with such sudden manifestations of light and heat, as implied some rapid change taking place in their chemical constitution and consistence. If shooting stars are of this nature, then, in those cases in which a great number of them appear in close succession, we have evidence that there is a region in which there is a large collection of matter of a nebulous kind, collected already into small clouds, and ready, by any additional touch of the powers that hover round the earth, to be further consolidated into planetary matter. That the earth's orbit carries her through such regions, in her annual course, we have evidence, in the curious fact, now so repeatedly observed, of showers of shooting stars, seen at particular seasons of every year; especially about the 13th of November, and the 10th of August. This phenomenon has been held, most reasonably, to imply that at those periods of the year, the earth passes through a crowd of such meteor-planets, which form a ring round the sun; and revolving round him, like the other planets, retain their place in the system from year to year.[7] It may be that the orbits of these meteor-planets are very elliptical. That they are to a certain extent elliptical, appears to be shown, by our falling in with them only once a year, not every half year, as we should do, if their orbit, being nearly circular, met the earth's orbit in two opposite points. That the shooting stars, thus seen in great numbers when the earth is at certain points of her orbit, are really planetoidal bodies, appears to be further proved by this;--that they all seem to move nearly in the same direction.[8] They are, each of them, visible for a short time only, (indeed commonly only for a few seconds), while they are nearest the earth; much in the same way in which a comet is visible only for a small portion of its path: and this portion is described in a short time, because they move near the earth. They are so small that a little change of distance removes them beyond our vision.