NEBULA. 41 



The nebula, in the midst of which lies the star 77 Argus, 

 which has become so celebrated for the alterations observed 

 in the intensity of its light, covers a space of more than four 

 sevenths of a square degree.^ The nebula itself, which is 

 divided into many unsymmetrical masses of unequal lumin- 

 ous intensity, nowhere exhibits the speckled, granular ap- 

 pearance which admits of the assumption of its resolvability. 

 It incloses a singularly shaped, oval vacancy, covered with a 

 faint glimmer of light. A fine delineation of the entire ap- 

 pearance, the result of two months' measurements, is given 

 in Sir John Herschel's Observations at the Cape.\ This 

 observer determined no less than 1216 positions of stars, 

 mostly from the fourteenth to the sixteenth magnitudes, in 

 the nebula of 77 Argus. These extend far beyond the nebula 

 into the Milky Way, where they stand clearly forth on the 

 deep black ground of the sky, and they are probably, there- 

 fore, unconnected with, and far removed from, the nebula it- 

 self. The whole contiguous portion of the Milky Way is, 

 moreover, so rich in stars (not clusters), that by means of the 

 telescopic star-gauges 3138 stars have been found for every 

 mean square degree between R. A. 9h. 50m. and llh. 34m. 

 These numbers even increase to 5093 in the sweeps for R. A. 

 llh. 24m., that is to ^ay, for one square degree of the firma- 

 ment, a number of stars greater than those which are visible 

 to the naked eye in the horizon of Paris or Alexandria, from 

 the first to the sixth magnitude. :j: 



The nebula in Sagittarius, which is of considerable size, 

 appears as if composed of four separate masses (R. Asc. 17h. 

 53m. ; N. P. Decl. 114° 21'), one of which is again three- 

 membered. All are interrupted by spots free from nebulous 

 matter, and the whole was imperfectly observed by Messier. § 



The nebulce in Cygnus are several irregular masses, one 

 of which forms a very narrow divided band, passing through 

 the double star ?/ Cygni. Mason was the first to recognize 

 the connection of these masses, so widely different, by means 

 of a singular cellular tissue. || 



The nebula in Vulpes was imperfectly seen by Messier (No 



* Cosmos, vol. iii., p. 177-179. 



+ Observ. at the Cape, § 70-90, pi. ix. Outlines, $ 887, pi. iv., fig. 2 



% Cosmos, vol. iii., p. 107. 



$ Observ. at the Cape, $ 24, pi. i., fig. 1, No. 3721 of the Catalogue 

 Outlines, § 888. 



II The nebula iu Cygnus, partly in R. Asc. 20h. 49m. ; N. P. Decl 

 58^ 27'. {Outlines, $ 891.) Compare Catalogue of 1833, No. 2092 

 pi. xi., fig. 34. 



