fifty thousand stars, each of the same brightness as the obvious star. What seems to the unassisted vision a nebula, a patch of diluted light, in which no distinct luminous point can be detected, may, by such an instrument, be discriminated or resolved into a number of bright dots; as the stippled shades of an engraving are resolved into dots by the application of a powerful magnifying glass. Similar results of the application of great telescopic power had of course been attained long previously; but, as the nature of scientific research is, each step adds something to our means of knowledge; and the last addition assumes, includes, and augments the knowledge which we possessed before. The discussions in which we are engaged, belong to the very boundary region of science;--to the frontier where knowledge, at least astronomical knowledge, ends, and ignorance begins. Such discoveries, therefore, as those made by Lord Rosse's telescope, require our special notice here. 4. We may begin, at what appears to us the outskirts of creation, the Nebulæ. At one time it was conceived by astronomers in general, that these patches of diffused light, which are seen by them in such profusion in the sky, are not luminous bodies of regular terms and definite boundaries, apparently solid, as the stars are supposed to be; but really, as even to good telescopes many of them seem, masses of luminous cloud or vapor, loosely held together, as clouds and vapors are, and not capable by any powers of vision of being resolved into distinct visible elements. This opinion was for a time so confidentially entertained, that there was founded upon it an hypothesis, that these were gaseous masses, out of which suns and systems might afterwards be formed, by the concentration of these luminous vapors into a solid central sun, more intensely luminous; while detached portions of the mass, flying off, and cooling down so as to be no longer self-luminous, might revolve round the central body, as planets and satellites. This is the _Nebular Hypothesis_, suggested by the elder Herschel, and adopted by the great mathematician Laplace. 5. But the result of the optical scrutiny of the nebulæ by more modern observers, especially by Lord Rosse in Ireland, and Mr. Bond in America, has been, that many celestial objects which were regarded before as truly nebulous, have been resolved into stars; and this resolution has been extended to so many cases of nebulæ, of such various kinds, as to have produced a strong suspicion in the minds of astronomers that _all_ the nebulæ, however different in their appearance, may really be resolved into stars, if they be attacked with optical powers sufficiently great.