CHAPTER VII.

NEBULÆ AND THE SYSTEM OF THE UNIVERSE.

A

MONG the strange objects revealed to the eye in

the heavens, the nebulæ may be considered, next to comets, the strangest and the most mysterious; and to the astronomer, perhaps, in reference to the system or plan (if it may be so termed) of the universe, of which they appear to be the indicators or sounding lines, the most interesting and important. Faint blueish misty clouds, hence called nebulæ, of definite form and shape, standing generally, as it were, aloof from every other celestial object, as though they did not belong to their companion stars around them, from the midst of which sometimes their pale mysterious forms may be seen looming and looking downwards, of every strange and fanciful shape,-now as a huge planet, larger than our full Moon, surrounded by a misty envelope; now as a faint ring, with black or white centre, or a double ring, each intersecting the other; now as a huge whirlpool of pale light, with concentric rings one within the other, or a spiral form like ostrich feathers, uniting in the centre and blown round by the wind in the same direction, like the bent sails of a windmill; now even a human face of misty light, with eyes and nose and mouth

of pale blue, and surrounded by bristly hair, actually peers at us out of the depths; sometimes too of a straggling undefined form, as that vast one in Orion, with patches of varied light; now a huge crab walks the shoreless sand of heaven, and spreads its legs of light on every side; now we have a dumb bell; now a beautiful garland of flowers, which resolves itself into stars of many colours, but one and all of such an enormous size, compared to the largest or most brilliant star in the heavens, as apparently to separate them from those bodies entirely as a class. To Sir William Herschel is owing that some of the mysteries attached to these strange bodies are cleared up; and on examining them with his powerful telescope, numbers of them were straightway resolved into myriads of stars like those around them in short, what appeared to be a separate firmament was disclosed. Some of them, however, did not yield even to the power applied to them, and to these Sir W. Herschel gave the name of irresolvable nebulæ. And here an ordinary observer would have concluded that it was only want of power in the telescope that prevented these last from being resolved like the others into their component stars. Sir William Herschel, however, did not arrive hastily at this conclusion, but by certain indications which his wonderful power of observation and experience enabled him to remark, he came to the conclusion that the cause of the irresolvability of many was, not their greater distance, but the fact that all were not firmaments of stars, but some were gaseous bodies. He was enabled, however, to come to a conclusion in his own mind, from his observations of these bodies generally, that they revealed the system of the universe

in infinite space; which was not, as was or might be supposed, an infinite or vast continuance of stars, but a possibly infinite number of separate star systems or galaxies, each constituting a vast island of stars or suns, so to speak, in the heavens, and separated from each other by such enormous distances, that the aggregates alone could be perceived as a faint misty light, until resolved by the highest power of which the telescope is capable. This system of the universe was recognised and adopted by astronomers universally, to the present day, with the exception of the question whether any of those termed by Herschel gaseous in nature, were so, and were not rather more distant, and hence irresolvable nebulæ.

This question was agitated much about twenty years ago, when Lord Rosse's powerful telescope resolved many which had been irresolvable by Sir W. Herschel's forty-feet telescope, and appeared to countenance the fact that there were no nebule to which the term gaseous could be applied: all were firmaments. This supposed discovery, however, did not affect the general question of the system of the universe as laid down by Herschel; and so matters continued until the discovery of the spectroscope, when the whole fabric thought to be established by Lord Rosse's telescope, again fell, and the positive existence of many gaseous nebulæ has restored the original theory propounded by the sagacious Herschel, so far as that fact is concerned; but it has remained for the present age now to question even the reality of the system of separate galaxies suggested by the great astronomer on the testimony of nebulæ, and to bring forward the nebulæ themselves as witnesses