THE STELLAR UNIVERSE. 



393 



powerful telescopes so plainly that the individual stars which compose them 

 can be distinguished, and these accordingly are called resolvable nebula ; that 

 some more remote give doubtful appearances in the telescope, leaving the ob- 

 server convinced that a little greater proximity of the object, or a little greater 

 power of the telescope, would render the stars composing them distinctly 

 visible ; that others, still more remote, are at such enormous distances as to 

 present no appearance, even to instruments of the greatest powers, except that 

 of a faint nebulous patch ; and finally, that every augmentation of the power 

 of telescopes will resolve a greater number of these nebulae into distinct stars, 

 and bring others which now can not be seen at all into view ; and that this 

 progression will go on without limit, the universe still expanding wider and 

 more wide into the depths of infinite space, before the increasing power of 

 science. 



But is this all which can be inferred ? That innumerable clusters may ex- 

 ist at such distances as only to appear as nebulous patches, even under the 

 space-penetrating power of instruments so colossal as those of Sir William 

 Herschel, and the more recent ones constructed by Lord Rosse, can not be 

 disputed ; but are all nebulous appearances of this character 1 Distance is 

 indisputably a cause of nebular phenomena, but is it the only cause ? This is 

 a question which will require some discussion. 



Sir William Herschel, who was the first to explain the phenomena of clus- 

 ters and nebulae by the supposition of distinct and separate masses of stars 

 removed to such a distance as to subtend a small visual angle, was also the 

 first to raise a doubt whether this cause alone be sufficient to explain all the 

 nebular phenomena. After long, patient, and minute surveys of the heavens, 

 he was at last impressed with the belief that certain appearances indicated also 

 the actual existence of luminous matter in situations comparatively near to us, 

 and presenting the same or nearly the same appearance as masses of stars 

 would whose distinctness would melt away in the magnitude of their distance. 

 Among the phenomena which suggested this idea, the most prominent were 

 those of nebulous stars. These objects appear as a bright stellar point, some- 

 times of the seventh or eighth magnitude, surrounded by a faintly luminous 

 atmosphere of several minutes diameter. The star appears exactly in the 

 centre, and the atmosphere around it perfectly circular in its outline is so 

 diluted, faint, and equal throughout, as to suggest no idea of its consisting of 

 stars. " If," says Sir William Herschel, " the nebulosity in this case consists 

 of stars, appearing nebulous because of their distance which causes them to 

 run into each other, what must be the size of the central body, which, at so 

 enormous a distance, yet so far outshines all the rest ? In the next place, if 

 the central star be no bigger than common, how very small and compressed 

 must be the other luminous points which send us only so faint a light ? In 

 the former case the central body would far exceed what we call a star ; and 

 in the latter, the shining matter about the centre would be too small to come 

 under that designation. Either, then, we have a central body, which is not a 

 star, or a star involved in a shining fluid of a nature wholly unknown to us." 



There is one other supposition which will suggest itself. The central 

 bright star may be immeasurably nearer to us than the cluster which, by its 

 enormous distance, is reduced to a luminous haze, and may be projected upon 

 it in the direction of the visual ray. Against this is to be advanced the im- 

 probability of such a casual projection, throwing the nearer star into the 

 mathematical centre of the distant cluster. Such an accident might possibly 

 occur in one or two instances, but we find it taking place in all cases of nebu- 

 lous stars. In some parts of the heavens these stars appear in considerable 

 numbers. Sir John Herschel mentions the nebulae surrounding the quadruple 



