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whatever doubts we may have respecting the actual habitudes prevailing there, we may be sure that they are fully as well suited to the wants of the inhabitants of those systems as are terrestrial habitudes to the wants of the inhabitants of earth.
The nebulæ again afford an interesting subject of speculation. Some of these objects have been shown by spectroscopic analysis to shine with true stellar light, while others are simply immense masses of incandescent gas. It is a moot point amongst astronomers whether we are to regard nebulæ of the former sort as belonging to our own sidereal system, or as lying far beyond it-forming, in fact, to use the expressive verbiage of German astronomers, vast island universes' scattered throughout the sea of space.' Nor does it greatly signify, so far as our present subject is concerned, which view we take. For if it should be proved that no outlying universes have yet been seen by man, yet every astronomer who recognises the true teaching of his science holds that our sidereal system is no more to be regarded as the only sidereal system of the universe, than our sun is to be regarded as the only sun in the sidereal system. Beyond that system, then, we look into the outlying spaces, and still the mental eye sees myriads of worlds richly stored with endless forms of life.
What opinion we are to form respecting the gaseous nebulæ, or respecting their correlatives in our solar system—the comets—it would at present be difficult to say. Until we know the purposes which these objects subserve in the economy of the universe, it would not be easy to indicate their association with the question of other inhabited worlds. Our knowledge respecting the actual nature of these bodies is too recent to permit us to speculate respecting their functions.
THE ROSSE TELESCOPE SET TO NEW
The great Rosse telescope, with its monster tube down which a tall man can walk upright, and with a light-gathering power so enormous that even by day the stars seen through it shine like miniature suns, has not remained idle since the lamented death of the astronomer who constructed it. Not only has the work to which Earl Rosse devoted it—the delineation of those strange stellar cloudlets that fleck the dark vault of the heavens--been continued with unrernitting assiduity, but its unrivalled powers have been devoted to aid the progress of those new and subtle modes of research which have recently been invented. The task was no simple one. The gigantic tube, with its ponderous six-feet mirror, had been poised so skilfully that a child could guide its movements. But for the new work which it was to be called on to perform much more was wanted. A new power had to be given to the telescope—a power of self-motion so exactly regulated that the gigantic eye of the telescope might remain steadily fixed on any given star or planet, notwithstanding the swift rotation of the earth, by which in the ordinary condition of the tube, the celestial objects are carried in a few moments across its field
of view. This power has now been given to the great reflector, and thereby the value of the instrument as an aid to scientific research has undoubtedly been more than doubled. Already it has solved a question which had been found to lie far beyond the powers of inferior instruments; and what it has done is, we believe, the merest foretaste of what it is likely to do in coming years.
Let us briefly consider a few of the qualities of this wonderful telescope, so that we may be able to appreciate its unequalled adaptability to the subtle modes of research which our physicists are now applying to the celestial bodies.
As a light-gatherer the Rosse reflector is facile princeps among telescopes. Sir William Herschel's great four-feet reflector and Lassell's equally large telescope come next to it; but the power of either of these instruments is less than one half that of the Parsonstown reflector, the illuminating surfaces of their mirrors being, in fact, exactly four-ninths of that of the Rosse telescope. It is, however, when we compare the power of the great mirror with that of the unaided eye, that we see its enormous capability as a light-gatherer. On a very moderate computation the light-gathering power of this wonderful instrument is found to be upwards of twenty thousand times that of the unaided eye; and it follows that if the faintest star visible to the unaided eye were removed to 140 times its present distance, it would still remain visible to the giant eye of the Rosse reflector.
If the other qualities of the great telescope were all proportioned to the one we have been considering, we might leave the reader to conceive what its powers would be, from the simple consideration that any celestial object would appear as distinctly when seen by its aid as it would if the unaided eye were brought to only one-140th of its actual distance from the object. Unfortunately this would be largely to overestimate the telescopic'powers of the instrument. We have spoken of its strength, we have now to speak of its weakness; and the inquiry is rendered so much the less unpleasing by the consideration that in some of the new modes of research to which the telescope is to be applied, the faults which are inseparable from a reflector of such enormous aimensions are of comparatively small moment.
The fault, then, of the Rosse reflector, as of all very large reflectors hitherto constructed, is that it does not present objects in a perfectly distinct manner. It used to be remarked of the great four-feet reflector of Sir William Herschel, that it'bunched a star into a cocked hat;' and it is whispered that Lassell's great mirror once exhibited an occultation of one of Saturn's satellites when no such phenomenon had in reality taken place. The fact seems to be that in the present state of mechanical science, it is impossible to construct a reflector of such enormous dimensions as these, with that perfect truth of figure which Mr. De la Rue has given to his 13-inch reflector, and which Mr. With seems able to give, in every instance, to the mirrors