Clusters and Nebulas. 265 



optician, speaks of having seen two of them, and added a fresh 

 one in 1857 with his enormous object-glass of 2 If inches, about 

 which such conflicting opinions have been expressed, and so 

 little seems to be really known. This last may, perhaps, be 

 the star discovered also by Lassell in 1862. It, appears, how- 

 ever, from the researches of Otto Struve, that other minute stars 

 in this region show variable light ; a circumstance, as he re- 

 marks, sufficiently singular in connection with their position in 

 the central part of this wonderful nebula ; and whatever fault 

 may be justly found with Schroter's figure, on comparing it with 

 those of Herschel and Bond, I am inclined to think that it 

 points to the same conclusion. It has been noticed, as far back 

 as Pond's day, that the interior of the trapezium is compara- 

 tively free from nebulous matter ; and this does not seem to be 

 a mere effect of contrast : on the other hand, an isolated star 

 lying N. of the mouth of the great dark gulf was discovered by 

 Mairanin 1731 to be encompassed by a haze, and has continued 

 so ever since. The whole extent of the nebulous glow appears 

 very considerable ; much greater, from its undefined character, 

 than might at first be supposed. By giving a rapid motion to 

 his telescope, so as to induce the effect of contrast, Secchi has 

 succeeded in tracing it through a space which may be described 

 as roughly triangular, with a base of nearly 4° and a height of 

 more than 5|°, reaching from its apex at £ Ononis, with a 

 break about cr, almost as far as v ; and a great part of this 

 feeble light has been perceived by Goldschmidt with a little tele- 

 scope of not much more than three inches aperture. A special 

 investigation by the present director of Harvard University, 

 the son of the late W. 0. Bond, into the arrangement of 

 the more luminous portion, has induced him to conclude that, 

 notwithstanding its apparent confusion and real intricacy, it 

 may be decomposed into a number of curved wisps or wreaths, 

 of which he has distinctly traced about twenty, indicating a 

 spiral structure, similar to that which the Earl of Bosse has de- 

 tected in so many nebulas, and which has been repeatedly found 

 associated with a stellar constitution. Secchi also observed a 

 spiral curve around one of the stars. 



This summary of modern discoveries has extended itself to 

 a length for which it is hoped that the exceeding interest of the 

 subject may be a sufficient apology. It is to be regretted that 

 the amount of optical power required for these researches is not 

 likely to be at the disposal of many of our readers. They need 

 not, however, be altogether discouraged. My comparatively 

 small aperture shows sufficiently well the peculiar appearance 

 which Lassell has described as masses of very light clouds, 

 packed one behind another, their edges being very light and 

 filmy, so that the sky is evidently seen through, or like little 



