16 



the observer's eye. If, therefore, it has taken so long a time, 

 and been so difficult to trace the fluctuations in the nebula of 

 Orion with the late Earl of Itosse's six feet speculum, and the 

 fine refractor with 15 inches aparture of the late Professor 

 Bond, how much greater aud more apparent must be the 

 alterations which are taking place in the nebula around ?? Ai'gus 

 to be discovered with a five feet refractor with only four 

 inches clear aperture. These singular and newly-discovered 

 motions in nebulous masses at so remote a distance, are well 

 calculated to open up new inquiries into the physical and 

 dynamical laws which determine the conditions and relations 

 of the forces which produce them. The singularity of the 

 nebulous portion of this region has but recently been made a 

 subject of systematic examination, and but for the observa- 

 tions and beautiful monograph of Sir John Herschel 

 the pecularities attached to it might have remained unknown 

 for a long time to come. In 1677 the star rj was recorded by 

 H alley as of the 4th magnitude. Its maximum was first 

 noted by Burchell in 1827, it being then of the 1st magnitude, 

 and on the 30th March, 1863, it was found for the first time 

 reduced to the 6th magnitude. Independent, however, of the 

 variability of the star itself, there is a much more singular 

 property belonging to the surrounding nebula, the particular 

 features of which I now purpose to describe. The mutability 

 of the nebula will be best made apparent by the accompanying 

 drawing, which will at once shew the different forms of the 

 dark space, and the relative position of v Argus to it, from 

 1834-7 to 1868. It must not be considered, however, that the 

 positions and characters here given are the only ones in which 

 the object has appeared ; a system of photographs only would 

 be the means of assisting materially the recognition of a 

 principle of irregularity pervading the whole structure. The 

 missing portion of the nebulous matter, as compared with the 

 Cape Monograph, may be thought by some to be owing to the 

 want of a larger optical power, but when the same instru- 

 ments have been used throughout this objection as to varia- 

 bility must fail to have any weight. The principal instrument 

 used is a 5ft. equatorial by Dallmeyer. The building being 

 situated in a garden the view of a small portion of the cir- 

 cumpolar stars is intercepted by fruit trees — to make good 

 this want a five feet portable refractor by Yarley is used in 

 the open air, so that the object has been watched and noted 

 throughout its entire revolution round the pole. The eye- 

 pieces in general use, and found most suitable for this purpose, 

 are a comet one of 28, and orthoscopic of 45, and an annular 

 micrometer of about the same power. A more powerful 

 instrument, would, no doubt, at any one observation, alter the 



