79 



no two very dissimilar telescopes will show nebulous matter 

 alike ; lake, for instance, the nebulee as portrayed by the Earl 

 of Rosse with those of Sir J. Herschel, and compare them 

 together with the drawings of G. P. Bond. The instruments 

 used by these observers respectively were a 56 feet reflector, 

 with 6 feet speculum ; a 20 feet reflector ; and an achromatic 

 of 22 feet 6 inches in length, with an object glass 15 inches in 

 diameter. The difference between them leads to much confu- 

 sion in Guillemin's fine book of the heavens. I have also a 

 strong opinion that the variations in the position of this 

 fluctuating object will have more or less effect in the sketches 

 made of it at different times. 



The Astronomer Royal takes exception to my drawings on 

 the ground of inaccuracy in points of geometry. If Mr. Le 

 Seur's opinion that the star t? shines with the light of burning 

 hydrogen, and has consumed the nebula, is thought to be 

 correct ; or, if the communicated opinions of Dr. Halley and 

 the late two Herschel's that a nebula may concrete into indi- 

 vidual stars, are of any account, how can geometry be applied 

 to the object under consideration without certain fixed points? 



An elaborate paper, with a drawing, has been prepared by 

 H. C. Russell, Esq., B.A., the Government Astronomer of 

 New South Wales, and read at a meeting of the Royal Society 

 of that colony, which I lay on the table. Mr. Russell, while 

 doing full justice to the object with the Sydney telescope, has 

 given due credit to the observations previously made at 

 Hobart Town. 



If the Astronomer Royal had offered some opinion as to 

 the cause of the fluctuations of this extraordinary and 

 interesting object it would have been a boon to physical 

 astronomy. 



As regards the accuraey of the Hobart Town drawings I 

 can refer to Mr. Piguenit, of the Survey Department, who is 

 now present, by whom they were checked and confirmed 

 previous to their transmission to the Royal Astronomical 

 Society. 



The following is a reply to the notes and queries made by 

 the Astronomer Royal on the " Observations of v Argus and 

 its nebula." Monthly Notices, R.A.S., for June 9th, 1871, 

 pp. 233 and 234:— 



"Note 1. — See in particular the line of four stars convex towards 

 17 Argus. 



"These stars have retained their apparent position, <fec., more 

 than any others in the same object, although variations to a small 

 degree have taken place. In carefully looking over the drawings it 

 will be found that a similarity exists in the position of many of the 

 stars, but as a rule some changes have taken place. 



