344 Clusters and Nebulce. 



in striking contrast to the generality of these objects, bears 

 remarkably well. I used to notice repeatedly with my former 

 achromatic a frequent fluctuation of light, or twinkling, as it 

 were, of the whole mass, much like the flickering of a gas 

 illumination beneath a gentle breeze ; and I still perceive it 

 with my larger aperture. Its form is distinctly elliptical : 

 Arago says as 83 to 100 ; Lassell gives 68" x 89" from actual 

 measurement. Herschel I. considered it resolvable ; his son 

 found the edges not quite sharply defined, and discovered a 

 nebulous light in the interior,* but did not perceive in its mottled 

 aspect any sign of resolution. The Earl of Eosse, when he 

 brought powers of 600, 800, and 1000 to bear upon it in his 

 3-foot reflector, found the internal light collected into wisps 

 or stripes, and saw branching appendages at the outer margin, 

 but he did not feel confident as to its resolvability ; and eight 

 subsequent observations with the 6-foot speculum, notwith- 

 standing Humboldt's assertion to the contrary, still left the 

 matter doubtful. Bond, with the great American telescope, 

 recognized many stars in it. Secchi seems to have been still 

 more successful with his clearly- defining achromatic in the 

 Roman air; he says that in 1854 he resolved it entirely "en 

 tres petits points lumineux brillants comme une poussiere 

 d' argent tres fine," observing at the same time that its light 

 is feeblest at the ends of the longer axis; and this result has 

 subsequently been confirmed b}^ Chacornac in the use of the 

 great FoiTcault silver-on-glass reflector of about 2i feet in 

 diameter. He resolves it into a mass of stars, of which the 

 brightest lie at the extremities of the inner axis ; the nebulous 

 veil across the opening he also sees transformed into a thin 

 layer of stars, and mentions a singular sensation of giddiness 

 as the result of the twinkling of such a multitude of luminous 

 points. There is nothing surprising in this ; but it is matter 

 of surprise indeed to learn that the investigations of Huggins, 

 carried on by means of the spectroscope, lead to a most op- 

 posite conclusion. This observer, whose researches, in con- 

 junction with Dr. Miller, into the constitution of the stars, are 

 attracting so much and such deserved attention, found, in 

 turning his instrument upon this nebula, that in common with 

 several others of somewhat similar aspect, its light had a com- 

 position entirely unlike that of the stars, so far as they have 

 been hitherto examined. It exhibited no trace of any of those 

 metallic elements whoso existence is so probable in them as 

 well as in our sun ; but, on the contrary, gave indications which, 

 from their similarity to those of some terrestrial materials, 



* This had, however, been previously noticed by Sehioter and Von Jlahn ; the 

 former also thought ho saw changes in this nebula. 



