If our desire of knowledge did not quicken as its sphere expands, or if man, so long as an eminence is unsurmounted, could lay himself down in peace, satisfied with the view of the vastness and variety which already stretch out beneath him, doubtless our task had now ended, and the volume of Astronomy might have been closed. But Desire, happily insatiable, has no confine on this side the Infinite; and no sooner have we reached the elevation of one thought or idea which resolves some large portion of the unknown, than ambition is fired afresh, and speculation never at rest, takes wing towards remoter regions.

In the present instance indeed there is every encouragement to further venturous inquiry. The Nebular Hypothesis, in its relations to the planetary system, may be termed complete;—it comprehends its beginnings, establishes those elements on which its duration depends, and exhibits the causes and mode of its ultimate transition into a novel form; and thus—surveying it from its commencement to its close—we are as if in possession of that primeval Creative Thought which originated our system and planned and circumscribed its destiny. Now, in reference to one of these epochs, our Hypothesis seems to hold equal connexion with the whole contents of the Heavens,—the epoch, viz.