NEBULvE. 17 



circumstance which distinguished it from the nebulous stars 

 in Cancer, and from other nebulous clusters. All that could 

 be recognized was a whitish glimmering appearance, bright- 

 er in the center, and fainter toward the margins. With a di- 

 ameter of one fourth of a degree, the whole resembled a light 

 seen from a great distance through half-transparent horn 

 plates (similis fere splendor apparet, si a longinquo cande- 

 la ardens per comic pellucidum de noctu cernatur)." Si- 

 mon Marius hazards a conjecture whether this singular star 

 be not of recent formation, # but will not give a decided opin- 

 ion, although it strikes him as singular that Tycho Brahe, 

 who had enumerated all the stars in the girdle of Andromeda, 

 should have said nothing of this nebulosa. The Mundus Jo- 

 vialis, which first appeared in 1614, indicates, therefore, as I 

 have already observed elsewhere,* 1 the difference between a 

 nebulous spot unresolvable by the telescopic powers of that 

 age, and a cluster of stars,! to which the mutual proximity of 

 its numerous small stars, not visible to the naked eye, imparts 

 a nebulous luster. Notwithstanding the great improvements 

 made in optical instruments, the nebula in Andromeda was 

 considered for nearly two centuries and a half — as at its dis- 

 covery — to be wholly devoid of stars, until two years since, the 

 transatlantic observer, George Bond, of Cambridge, in Massa- 

 chusetts, discovered 1500 small stars within the limits of the 

 nebula. I have not hesitated to class it among the stellar 

 clusters, although the nucleus has not hitherto been resolved 4 

 It is probably only to be ascribed to some singular acci- 

 dent that Galileo, who, when the Sidereus Nuntius appear- 

 ed in 1610, had already made frequent observations of the con- 

 stellation of Orion, should have subsequently mentioned, in 

 his Saggiatore, no other nebulae in the firmament but those 

 which his own weak optical instruments had resolved into 

 stellar clusters, although he might long before have learned, 

 through the Mundus Jovialis, of the discovery of the starless 

 nebula in Andromeda. When he speaks of the nebulose del 

 Orione e del Prescpe, he understands by the expression merely 

 "aggregations (coacervazioni) of innumerable small stars. "$ 

 He successively delineates, under the deceptive designations of 

 nebidosce capitis, cinguli, et ensis Orionis, clusters of stars, 



* 



Cosmos, vol. ii., p. 320. 

 t Germ., Sternhaufen ; French, amas d'etoiles. 

 t Cosmos, vol. iii., p. 142. 



§ Galilei notd che le Nebulose di Orione null 1 altro erano die mucchi e 

 coacervazioni (V innumerabili Stelley — Nelli, Vita di Galilei, i., p. 208- 



