Mean-while, two other distinct periods of meteoric showers have, as already intimated, been determined; namely, about the ninth of August, and seventh of December. The facts relative to the history of these periods have been collected with great industry by Mr. Edward C. Herrick; and several of the most ingenious and most useful conclusions, respecting the laws that regulate these singular exhibitions, have been deduced by Professor Twining. Several of the most distinguished astronomers of the Old World, also, have engaged in these investigations with great zeal, as Messrs. Arago and Biot, of Paris; Doctor Olbers, of Bremen; M. Wartmann, of Geneva; and M. Quetelet, of Brussels. But you will be desirous to learn what are the _conclusions_ which have been drawn respecting these new and extraordinary phenomena of the heavens. As the inferences to which I was led, as explained in the twenty-sixth volume of the 'American Journal of Science,' have, at least in their most important points, been sanctioned by astronomers of the highest respectability, I will venture to give you a brief abstract of them, with such modifications as the progress of investigation since that period has rendered necessary. The principal questions involved in the inquiry were the following:--Was the _origin_ of the meteors within the atmosphere, or beyond it? What was the _height_ of the place above the surface of the earth? By what _force_ were the meteors drawn or impelled towards the earth? In what _directions_ did they move? With what _velocity_? What was the cause of their _light_ and _heat_? Of what _size_ were the larger varieties? At what height above the earth did they _disappear_? What was the nature of the _luminous trains_ which sometimes remained behind? What _sort of bodies_ were the meteors themselves; of what _kind of matter_ constituted; and in what manner did they exist _before they fell to the earth_? Finally, what _relations_ did the source from which they emanated sustain to our earth? In the first place, _the meteors had their origin beyond the limits of our atmosphere_. We know whether a given appearance in the sky is within the atmosphere or beyond it, by this circumstance: all bodies near the earth, including the atmosphere itself, have a common motion with the earth around its axis from west to east. When we see a celestial object moving regularly from west to east, at the same rate as the earth moves, leaving the stars behind, we know it is near the earth, and partakes, in common with the atmosphere, of its diurnal rotation: but when the earth leaves the object behind; or, in other words, when the object moves westward along with the stars, then we know that it is so distant as not to participate in the diurnal revolution of the earth, and of course to be beyond the atmosphere. The source from which the meteors emanated thus kept pace with the stars, and hence was beyond the atmosphere.