It has been remarked that the best evidence of the truth of a theory, is its ability to refer to some general principle, the greatest number of relevant phenomena, that, like the component masses of the chiselled arch, they may mutually bind and strengthen each other. This we claim to be the characteristic of this theory. At the outset it was not intended to allude to more than was actually necessary to give an outline of the theory, and to introduce the main question, yet untouched. We have exhibited the stones of which the arch is composed; but they may be pasteboard,--for the reader has not handled them. We will now produce the keystone, and put it in its place. This he shall handle and weigh. He will find it hard,--a block of granite, cut from the quarry of observed facts, and far too heavy to be held in its place by a mere pasteboard structure. ENUNCIATION OF THE THEORY. Quitting, therefore, the region of the planets, we will come down to the surface of our own globe, to seek for some more palpable evidence of the truth of the following propositions: 1st. That space is filled with an elastic fluid, possessing inertia without weight. 2d. That the parts of this fluid in the solar system circulate, after the manner of a vortex, with a direct motion. 3d. That there are also secondary vortices, in which the planets are placed. 4th. That the earth is also placed in a vortex of the ethereal medium. 5th. That the satellites are passively carried around their primaries, with the ethereal current, and have no rotation relative to the ether, and therefore they always present the same face to their primaries, and have no vortex. The consideration of these propositions involves many others, many difficulties, many apparent anomalies and contradictions, which should bespeak for such a theory,--the offspring of observation, without the aid afforded by the knowledge of others, and of toil without leisure,--a large share of indulgence. With this we will close these preliminary remarks, and present our theory of the physical cause which disturbs the equilibrium of our atmosphere, and which appears the principal agent in the production of storms, in the following words: The dynamical axis of the terral vortex passes through the centre of gravity of the earth and moon, and is continually circulating over the earth's surface in both hemispheres, in a spiral,--its latitude and longitude, at any particular time, being dependent,-- 1st. On the relative mass of the moon. 2d. On the inclination of the axis of the vortex to the earth's axis. 3d. On the longitude of the ascending node of the vortex on the lunar orbit. 4th. On the longitude of the ascending node of the lunar orbit on the ecliptic. 5th. On the eccentricity of the lunar orbit at the time. 6th. On the longitude of the perigee of the lunar orbit at the time. 7th. On the moon's true anomaly at the time. MASS OF THE MOON.