CLUSTERS 9F STARS. 143 



of Cambridge, United States (March, 1848), and testifies to 

 the admirable illuminating power of the refractor of that Ob- 

 servatory, which has an object-glass fifteen inches in diam- 

 eter ; since even a reflector with a speculum of eighteen inch 

 es in diameter did not reveal " a trace of the presence of a 

 star."* Although it is probable that the cluster in Adrom- 

 eda was, at the close of the tenth century, already recorded 

 as a nebula of oval form, it is more certain that Simon Ma- 

 rius (Mayer of Guntzenhausen), the same who first observed 

 the change of color in scintillation,! perceived it on the 1 5th 

 of December, 1612 ; and that he was the first who described 

 it circumstantially as a new starless and wonderful cosmical 

 body unknown to Tycho Brahe. Half a century later, Bouil- 

 laud, the author of Astronomia Philolaica, occupied himself 

 with the same subject. This cluster of stars, which is 2^- 

 in length and more than 1 in breath, is specially distinguish- 

 ed by two remarkable very narrow black streaks, parallel to 

 each other, and to the longer axis of the cluster, which, ac- 

 cording to Bond's investigations, traverse the whole length 

 like fissures. This configuration vividly reminds us of the 

 singular longitudinal fissure in an unresolved nebula of the 

 southern hemisphere, No. 3501, which has been described 

 and figured by Sir John Herschel. (Observations at the 

 Cape, p. 20, 105, pi. iv., fig. 2.) 



Notwithstanding the important discoveries for which we 

 are indebted to Lord Rosse and his colossal telescope, I have 

 not included the great nebula in Orion's belt in this selection 

 of remarkable clusters of stars, as it appeared to me more ap- 

 propriate to consider those portions of it which have been re- 

 solved in the section on Nebulae. 



The greatest accumulation of clusters of stars, although 

 by no means of nebulas, occurs in the Milky WayJ (Galaxias, 



* Outlines, $ 874, p. 601. 



t Delambre, Hist, de VAstr. Moderne, t. i., p. 697. 



t We are indebted for the first and only complete description of the 

 Milky Way, in both hemispheres, to Sir John Herschel, in his Results 

 of Astronomical Observations, made during the Years 1834-1838, at the 

 Cape of Good Hope, 316-335, and still more recently in the Outlines 

 of Astronomy, 787-799. Throughout the whole of that section of the 

 Cosmos which treats of the directions, ramifications, and various con- 

 tents of the Milky Way, I have exclusively followed the above-named 

 astronomer and physicist. (Compare also Struve, Etudes d'Astr. Stel- 

 laire, p. 35-79 ; Madler, Ast., 1849, 213 ; Cosmos, vol. i., p. 103, 150.) 

 I need scarcely here remark that in my description of the Milky Way, 

 in order not to confuse certainties with uncertainties, I have not refer- 

 red to what I had myself observed with instruments of a very inferior 



