Clusters of Stars and Nebulce. 59 



similarity of magnitude in the individuals, are only partially 

 applicable. The forms of clusters and nebulae are indefinitely 

 varied ; many being elliptical, a few spiral, others perforated, 

 others again extended in length, branching, or contorted in 

 various figures, while their components are by no means always 

 all equally bright, the reverse frequently opposing a difficulty in 

 the way of complete resolution, when the telescope can master 

 the more resolvable portion, but leaves the smaller individuals 

 merged in a general haze. In another respect, too, our state- 

 ment requires qualification. It has been asserted that the 

 apparent minuteness of the individual stars in certain clusters, 

 as compared with others, may be the result of increased dis- 

 tance from the spectator, and the series which we have ima- 

 gined is based upon this idea. It was that of Sir W. Herschel, 

 who thus assigned the probable distances of nebulas, in progres- 

 sive remoteness, till they passed even beyond the space-pene- 

 trating power of his forty-feet reflector, which he estimated 

 one hundred and ninety -two times greater than that of the eye 

 — a value corresponding to three hundred thousand times the 

 distance of Sirius ! But this magnificent conception has been 

 entirely overthrown by more recent discoveries. It rested 

 upon the assumption that the distances of the stars are, on an 

 average, in the inverse ratio of their apparent magnitudes — an 

 assumption not merely recommended by its simplicity and 

 facility, but by its being probably the only one whose adoption 

 could lead to any positive or numerical result. Of late years, 

 however, its inadequacy has become more and more evident, 

 upon grounds so lately stated in the present publication (Intel- 

 lectual Obseever, xviii. 454), that they need not be repeated 

 here ; and now it must be admitted that after so many years 

 we find ourselves without a guide in the interminable wilder- 

 ness of nebulas. It is very possible that Sir W. HerscheFs 

 hypothesis may yet be correct as regards the majority of these 

 objects, and it is unquestionably supported by the evidence of 

 sense; but how deceptive this is has been demonstrated in the 

 case of insulated stars and systems, and analogy has begun to 

 lead us in an opposite direction. Analogy, with all its defi- 

 ciencies, is like the one-eyed man, who has been said to be a 

 king in the country of the blind; and reasoning from its indi- 

 cations where no others are attainable, we should have to con- 

 clude that the brightest and most resolvable clusters may be 

 possibly as distant from us as some of those little heaps of 

 ' ' star-dust," whose aspect would bespeak for them a far more 

 inconceivable remoteness, and that certain, again, of these latter 

 may be even nearer to our system than some of those great and 

 conspicuous stars, beyond which they were formerly placed at 

 an immeasurable distance. In fact, whatever may appear pro- 



