On the Nebula around Eta Argus. 17 



to the difference in the instruments. The Cape drawing being 

 always received as its appearance in a large telescope ; for this 

 drawing the observations extended over the years 183J?, 5, 6, 7, 

 and part of 8, and nothing was then seen to lead to the supposi- 

 tion that any change was going on in the nebula or stars. 



It is not surprising, then, that Mr. Powell, who appears to 

 have been the first to notice change in the nebula, attributed it 

 to his comparatively small telescope, and did not then publish 

 his observations. Amongst his photometric observations of Eta 

 are found these notes about the nebula. March 23rd, i860, 

 "nebula about Eta Argus magnificent; April 15th, 1860, nebula 

 much fainter than formerly ; March 23rd, 1860, again, ' Eta is 

 in a rough sketch placed outside the bright portion of the 

 nebula.' And the lemniscate is described as a cliannel. Several 

 entries follow, noting openness of the lemniscate on the south, 

 and greatly diminished brightness of the nebula. April 4th, 

 1862, Eta Argus beautifully round and clear out of the lemniscate 

 altogether; two patches of nebula with passage between them to 

 the left, or preceding." 



These were not published till May,' 1864 (R. A. S, notices), 

 after Mr. Abbott had published his observations ; to Mr. Abbott 

 is therefore due the credit of first publishing notice of a change 

 in. the appearance of the nebula. He had been observing the 

 star for a number of years ; but the first observation on the 

 nebula that I can find is dated May 22rd, 1863, and runs thus : 

 "A drawing made of the object Eta Argus quite distinct within 

 the dark space." This was given to the Eoyal Society of 

 Tasmania on the 9th June, 1863, in a paper on the " Variable 

 star Eta Argus." 



A further remark occurs in that paper to this effect : " Com- 

 paring the present description with the Cape drawing, it will, I 

 think, appear conclusive that the apparition of the surrounding 

 nebula is also variable." " The open space given in the Cape 

 monograph and also in the last addition of the outlines is some- 

 what in the form of a dumb-bell compressed in the centre and 

 surrounded with nebula, in the most dense part of which is 

 situated Eta Argus. The appearance of the open space now 

 assumes the form of a crooked billet, wide in the centre and 

 open at both ends, with Eta Argus situated 1' + within the open 

 space or dark part, and surrounded with an almost innumerable 

 quantity of brilliant stars, some of a blue and some of a ruddy 

 colour." 



In May, 1868, some additional observations and a drawing by 

 Mr. Abbott were published in the R. A. S. Notices. Sir John 

 Hereehel was very much interested, and carefully compared the 



