16 Cn the Nebula around Eta Argus. 



to increase, and was then equal to Alpha Centauri ; aftei' this it 

 faded gradually, and on the 14th of April was about equal to 

 Aldebaran. 



In 1813, Sir Thomas Maclear, at the Cape, observed it much 

 brighter than Alpha Centauri, and rather brighter than Canopus, 

 and on the 11th of March thought it almost equal to Sirius. As 

 Sir John Herschel estimated Canopus as double, and Sirius as 

 quadruple of Alpha Centauri, Eta was at that time probably 

 triple Alpha Centauri; it then faded again, but in 1815 was 

 brighter than Canopus, and had been so for some time. These 

 observations proved the extraordinary iluctuations of the light of 

 this star, and made it one of the most interesting objects in the 

 heavens and the observations of various astronomers since have 

 in no way tended to decrease the interest then excited. From 

 their published results I have, for convenient reference, drawn up 

 the attached list. It contains the observations from which 

 Professor Loomis, in April, 1869, deduced the generally accepted 

 period of 67 years, and some additional ones. 



Professor "Wolf, in 1863, thought that a period of forty-six 

 ■years would satisfy the observations ; but Professor Loomis 

 found that subsequent observations, especially those of Mr. 

 Tebbutt, could not be satisfied except by assuming a longer 

 period, and gives the result of his investigation in vol. xxviii 

 E. A. S. notices. His diagram exhibits minor fluctuations of light 

 which may, perhaps, in some cases be accounted for by errors in 

 the observations, but not in all ; and there can be no doubt that 

 Eta is subject to strange minor fluctuations of light in addition 

 to its periodical variation. 



Sir John Herschel,. (in 1843) (at page 36 of the Cape Observa- 

 tions) says, " A strange field of speculation is opened up by this 

 phenomenon — the temporary stars heretofore recorded have all 

 become totally extinct. Variable stars, so far as they have been 

 attended to, have exhibited periodical alterations, in some degree at 

 least regular, of splendour and comparative obscurity. But here 

 we have a star fitfully variable to an astonishing extent, and 

 whose fluctuations are spread over centuries. Its future career 

 will be a subject of high physical interest." Since 1845 Eta has 

 gradually faded, and is now (1871) only a 7th magnitude star ; 

 less than it has ever been observed before, and, perhaps, going 

 like all other temporary stars into darkness : certainly with its 

 fading light throwing many dark shadows in the way of any 

 speculations on the constitution of temporary stars. 



Of the nebula about it little notice seems to have been taken 

 for a number of years ; the difiiculty of dra^ving it would deter 

 most observers, and the diflerences observed naturally attributed 



