106 On rj Argils and Nebula. 



Aet. XXXII. — On r} Argils and Nebula. By 

 F. Macgeoege. 



[Bead 9th October, 1871.] 



The admirable sketch and description of this wonderful 

 object given by the late Sir John Herschel, and the catalogue 

 of the stars comprised in it, form together — as far as the 

 power of his 18-inch aperture could reach— a complete 

 record of the appearance of -q Argus and Nebula, between 

 the years 1834 — 1838. In that description he gives the 

 position of certain stars on the borders of the lemniscate or 

 central vacuity, close to the star 77, in these words: "Four 

 stars, Nos. 686, 603, 589, and 670 = w of the catalogue, are 

 placed precisely on its edges, and will serve as excellent 

 detectors of change in its form, should any occur. The 

 stars No. Q07 = t, 664< = v, and 6 J 6, though near the edge, 

 are yet fairly immersed in the Nebula, On the other hand. 

 No. 634, situated in the contraction of the oval towards its 

 middle, is yet fairly within the vacancy, and so situated, 

 that the slightest shifting of the nebulous contour at its 

 preceding side, cannot fail to be rendered sensible." This 

 piece of precise word-painting, added to the evidence of 

 the published engraving in Sir John's Cape observations, is 

 most valuable, since a comparison with the nebula, as seen 

 in 1871, will shew beyond doubt or cavil, the inapplicability 

 of such a description, and such a drawing to the present 

 appearance of the lemniscate outline in the Great Telescope. 

 The rough chalk sketch marked H, is a copy from part of 

 the inverted drawing of Herschel, re-inverted to suit ordinary 

 telescopes ; and I hope it will be distinctly understood that 

 this and the other five rough copies from the working- 

 drawings are the work of one hour, and only intended to 

 shew the salient points and the two or three stars referred 

 to, the rest being unimportant. 



From 1838 to 1869 no observations of the nebula around 

 77 of a trustworthy character could be made — owing to the 

 want of a telescope of sufficient power — although most 

 interesting and important observations of the star 7] itself, 

 and of the surrounding stars, have been made with small 

 apertures, and Mr. Tebbutt of New South Wales, in 

 particular, has in the A sir. 80c. Monthly Notices, for May last 

 given a list of magnitudes of 77 Argus from 1854 to 1870, which 



