EARL ROSSE’S OBSERVATIONS ON THE NEBULA. 
509 
and therefore they have been inserted at random to complete the general effect, and 
many minute details are still wanting to make the figure complete. 
As we have proceeded with our task of re-examining Sir John Herschel’s Cata- 
logue, several groups of nebulae have been discovered, although new objects have not 
been as yet sought for. In some cases a nebulous connection has been detected be- 
tween the individuals of the g’roup, in others not. Sketches have been made and 
some measures taken. The whole subject of the grouped or knotted nebulae is one of 
deep interest ; but we have not proceeded sufficiently far Avith it to make it worth 
Avhile to enter upon it in the present paper, and it only remains to point out a defect 
common to all the sketches which might mislead if not specially noticed. In sketch- 
ing AA^e necessarily employ the smallest amount of light possible, very feeble lamp-light, 
especially where the objects or their details are of the last degree of faintness. To 
see the sketch as we proceed it is often necessary to mark it too strongly : this would 
be of little moment if the excess of colour was alvA’^ays in the same proportion, espe- 
cially as different eyes form a very different estimate of the relative intensities of a 
nebula and its representation on paper, but it is not so ; the contrast between the 
faint and bright nebulse and between the faint and bright parts of the same nebula 
is very liable to be made too slight. The most important error to guard against is 
that of supposing that the well-marked confines of the nebula on paper really repre- 
sent the boundaries of the object in space in all cases. Frequently there is a very 
gradual fading aAvay at the edge, the last trace of which is either a luminous mist 
becoming rarer till imperceptible; a gauge-like tissue of the faintish imaginary floc- 
culi, or hairy filaments, which become finer and more scattered till they cease to be 
visible, showing that the real boundary has not been seen, and that the form of the 
object Avould alter if additional optical power could be brought to bear upon it. The 
same remark applies to the faint interior details, in most cases probably only in part 
seen. 
Plate XXXV. figs. 1 and 2 are seen on a scale of half an inch to a minute ; the 
others are on no regular scale : they are about the size of the figures Avhich accom- 
pany Sir John Herschel’s Catalogue, the smaller however have been somewhat 
enlarged Avhere there were details which otherAvise could not have been well repre- 
sented. 
Annexed are a few remarks relating to each figure, Avhich seem to make the in- 
formation conveyed by it more complete: they are for the most part extracts selected 
from our journal of observations ; in a few cases, hoAA^ever, to save space, merely the 
substance is given. 
Where the 3-feet instrument was employed it is specially mentioned; in every 
other case it was the 6-feet instrument. 
Plate XXXV. fig. 1, H. 1622. — This object has been observed twenty-eight times 
with the 6-feet instrument; it had been repeatedly observed previously Avith the 3-feet 
instrument. 
September 18, 1843. — Observed with the 3-feet instrument; poAver single lens. 
