E. S. EoUm—On supposed changes in Nebula M. 17. 



'e 

 strongly suggesting the 

 laea ot an absorption ol tde nebulous matter; and, 2. The much 

 feebler and smaller knot at the [northwestern] end of the same 

 branch, where the nebula makes a sudden bend at an acute angle. 

 With a view to a more exact representation of this curious nebula, 

 I have at different times, taken micrometrical measures of the 

 relative places of the stars in and near it, by which, when laid 

 down as in a chart, its limits may be traced and identified, as I 

 hope soon to have better opportunity to do than its low situation 

 in this latitude will permit." 



From Ast. Obs. at the Cape oj Good Nope .—Aher explaining 

 that his first figum is far from accurate Herschel says :— 



"In particular the large horseshoe shaped arc ... is tlRif 

 represented as too much elongated in a vertical direction and :i> 

 bearing altogether too large a proportion to [the eastern] streak 

 and to the total magnitude of the object. The nebulous diffu^i"|'- 

 too, at the [western] end of that arc, forming the [westeni] anp^' 

 and base-line of the capital Greek omega (iJ), to which the general 

 figure of the nebula has been likened, is now so little conspicuous 

 as to induce a suspicion that some real change may have taken 

 place in the relative brightness of this portion compared with the 

 rest of the nebula ; seeing that a figure of it made on June 25, 

 1837, expresses no such diffusion, but represents the arc as break- 

 ing off before it even attains fully to the group of small stars at 



