On the Nebula around Eta Argus. 21 



and corrected until it was deemed a faithful representation of it 

 as seen now. 



On comparing this with the Cape monograph startling differ- 

 ences are found ; not so great near Eta as some observers have 

 thought, but far greater than any which astronomers have before 

 witnessed. In the nebula in Orion the changes are so small as 

 to be with difficulty made out ; but here the densest part in 

 1834-8 is now one of the faintest, while close to this another part 

 of peculiar form has 'become the brightest patch in the nebula. 



Examining it more in detail, it is seen that the mass in which 

 the lemniscate (or dark enclosed space) is situated is in general 

 outline very much the same as it was thirty years since, and in 

 some of its marked features exactly the same ; as for instance, 

 the definite outline beginning at 70 s. — 240," and running still 

 exactly as Sir John Herschel has described it amongst some 

 small stars ; but round the border of the lemniscate great 

 changes iu the relative brightness of the diflFerent parts of the 

 outline have taken place, and some slight changes in the outline 

 itself; the greatest being at 17 seconds preceding — 100 seconds 

 where one point now occupies the space of two in the Cape 

 drawing ; and it is remarkable that it is just at this point that 

 the large Melbourne reflector reveals rapid change at the present 

 time ; the nebula also seems much brighter at this point than it 

 was in 1834-8, judging from the parts which appear unchanged. 



It is, however, at the south end and following side that the 

 most remarkable change has taken place, this end and half the 

 side have now become so faint, that with small telescopes no 

 nebula is seen at all ; while the other half of the same side has 

 so much increased in brightness that it is now the most marked 

 feature of the nebula, its outline on the preceding and north sides 

 being very like that in the Cape drawing, while the following and 

 south side of it form a curved line which seems faintly indicated 

 in the same drawing ; this is a very curious feature and seems to 

 indicate that this is a nebula seen upon the fainter one. It has 

 evidently become much brighter since 1834-8, and is, I think, one 

 of the principal causes of the increased visibility of the nebula, 

 being now always more conspicuous than any other part, and 

 visible when they are lost in twilight or haze. In other respects 

 this drawing seems to represent the same object as the Cape 

 monograph, allowing for difference in the telescopes. The star 

 jN^o. 11 (664 H) is just in the edge of the nebula ; and about 

 midway between it and Eta is another star about 15 magnitude, 

 not in this drawing or in the Cape list. 



Passing now to the branches we find changes even more surprising 

 than those already noted ; I think without a parallel, and pointing 



