On the Nehida around Eta Argus. 15 



Art. I. — On the Nebula aroiind Eta Argus, by H. C. 

 Russell, Esq., B.A. 



(Read May 12, 1871.) 



In the months of January and February of the present year I 

 surveyed carefully, with- the fine refractor of the Sydney Observa- 

 tory, the stars and nebula about the remarkable variable Eta 

 Argus. The observations I have already printed and sent to Sir 

 John Herschel, who has shown the greatest interest in the 

 changes which have from time to time been reported in this 

 object, and whose beautiful monograph of 1843 enables us 

 now to trace some of the most wonderful changes that have ever 

 been witnessed by astronomers. 



I then omitted some results of the survey, as I did not wish to 

 give anything as evidence which might be biassed by my personal 

 convictions. Upon these I have based the few remarks I have to 

 make this evening. And, as the subject may be new to some of 

 the members of this Society, a few historical notes may not be 

 out of place. 



In 1677, when observed by Halley, at St. Helena, Eta Argus was 

 of the fourth magnitude, thence to 1751 it does not appear to have 

 been observed, but in that year Lacaille called it second magnitude. 

 Another long interval and Mr. Burchell — 1811 to 1815 — noticed 

 that it was fourth magnitude. 1822 Fallows calls it second 

 magnitude, and in 1827 Burchell noticed that it had increased to 

 the first magnitude, and writing to Mr. J. Duncan, in 1827, says 

 " I am curious to know whether any one has observed that Eta 

 Argus which is marked as fourth magnitude, and, was always so 

 when I was in Africa, is now of the first magnitude, or as large 

 as Alpha Crucis." No one, however, but himself seems to have 

 noticed it, and he did not publish the fact. When Sir John 

 Herschel went to the Cape in 1831 he began his observations on 

 Eta Argus, which was then about the second magnitude, and 

 continued so up to November, 1837 ; on the 16th of December, 

 when again examining the star, he was very much surprised to 

 find it had increased to the first magnitude, and was one of the 

 brightest stars in the heavens. This, naturally, excited his 

 curiosity, and led him to watch it closely to the following April 

 (1838), when his departure from the Cape prevented further 

 observations of it. Up to the 2nd of January, 1838, it continued 



