Feb. 9, 1882] 
NATURE 343 
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the earlier, globular in the two later drawings. This 
difference, while reminding us of the ancient variations 
of Le Gentil, may possibly not imply much, where no 
distinct outline is presented to rectify the judgment of the 
eye. But we have something more tangible in the length 
and form of the canals. Here, assuming equal care on 
the part of Trouvelot in designing, with that claimed by 
Bond both in delineation and description, we seem to 
have indications of change. It is true that Bond’s account 
of the outer or shorter canal, as commencing a few minutes 
np the other, does not altogether agree with his drawing; 
but this is not the sole instance of confused ‘“‘orienta- 
tion” in his memoir ; and at any rate he describes its 
commencement as only 4’ of space distant from the 
other. Trouvelot, as will be seen, has extended it 
much further sf; and should it be objected that this 
slenderer termination may have escaped the eye of Bond, 
it is curious to find it strongly and independently confirmed 
by Perry in two sketches on different nights, and by his 
express statement that “the / rift extends further than 
the / rift on the southern side.’ The greater breadth 
which he has given in each sketch to both canals is also 
worthy of notice. Another point of disagreement between 
Bond and Trouvelot occurs in the form of the longer canal: 
the “ perfectly straight, suddenly terminated, and slightly 
diverging” sides, as far as the nucleus, of Bond’s descrip- 
tion, confirmatory of his drawing, according ill with the 
sinuous direction which Trouvelot has shown. 
This may suffice for the collation of the results obtained 
by great instruments. But acomparison yet remains with 
the appearance in smaller telescopes; and it will be found 
deserving of attention. Let our aperture be restricted to 
5 inches achromatic, or an equivalent light in a reflector: 
then, with ordinary vision and customary skies, the three 
salient points, the great centre, Le Gentil’s ball, and 
Caroline Herschel’s cloud, though much dimmed and 
contracted, keep their places, but all the attendant 
nebulosity will be swept away. Such at least is my 
own experience. On October 5, 1863, a few hours before 
the strong earthquake-shock, that will long be remembered 
in this part of England, I caught a portion of the inner 
canal with a 54 inch achromatic, and on August 24, 1864, 
I saw them both feebly, but certainly, with 8 inches of 
silvered glass, and have several times followed them with 
that mirror, and with my present 9} inch aperture, for a 
considerable length: but though traced, I cannot say that 
they would have been discovered. And latterly, whether 
from decay of visual power, or want of purer air, I have 
failed to detect them. But the general result is unmis- 
takable. Either Bond’s drawing must have exaggerated 
—and that materially—the light which they traverse; 
or that light must have since faded. The latter 
it must be owned is not probable. Yet his figure 
is fairly supported by his words, where he gives both 
canals near the nucleus as “ beautifully distinct,” and the 
light between them 2 as bright as on the inner side of the 
longer one, and his design makes both rifts cleave, not as 
now, the feeble diffusion, but the great mass, not far from 
its very heart. On the other hand it must be admitted 
that probably at a not much later date, Lord Rosse’s 
3-foot speculum showed a much greater contrast between 
the opposite sides of that canal; and Trouvelot comes 
much nearer to the present aspect of things: so that 
nothing very satisfactory can be deduced here. The case 
however may seem stronger with regard to Caroline 
Herschel’s nebula. There are discrepancies in the earlier 
values of its light. Her brother called it “ pretty faint”’ 
with an area of 30’ X 12’, proving that he included with 
it much of the great nebula. His son, reducing it to 
15’ X 7’, found it “pretty bright,” though it stands as 
“very bright” in the General Catalogue. Bond shows 
it of a brilliancy superior to all but the light near the 
great nucleus and the centre of Le Gentil’s ball. The 
Earl of Rosse, with the 6-foot mirror in 1876 complains 
of this delineation as ‘‘ far too bright and sharply defined.” 
Trouvelot again with a softer general effect has a small 
centre as bright as Bond; and this may perhaps be tae 
nucleus faintly suspected by Sir John Herschel, and 
described by Lord Rosse in 1855 as bright and sharp: 
while the cautious and accurate d’Arrest (186t—67) using 
an I1-inch object-glass, and giving its size 12’ X 23’, speaks © 
of it as only moderately bright, much more so towards the 
centre, but without a genuine nucleus. These details, 
needless and tedious as they may possibly at first appear, 
are introduced chiefly from their bearing on our present 
inquiry as to the probability of change, but in some 
measure as illustrative of the uncertainty that hangs 
about such observations. Every one may not be aware 
of the breadth of margin required, where there is no 
distinct outline, and faint diffusions fade out of all but 
the purest skies, and dilate and shrink by turns under 
the anxious gaze, and estimates of brightness are pre- 
carious, and artistic talent is often dissociated from the 
observer’s skill. But after all allowances there can be 
no doubt that the existing aspect of this (Miss Herschel’s) 
nebula with moderate telescopes is much less reconcilable 
with the designs of Bond and Trouvelot than might have 
been expected. 
We can neither at present push this line of inquiry 
further, nor say that it has been very successful. Had it 
yielded us distinct evidence of change either in form or 
brightness, it must of course have been accepted as decisive 
against a stellar constitution ; but we have only met with 
such probabilities as invite close and long research ; and 
it was with a view of stimulating such research that the 
present paper was undertaken. A few more remarks 
may be permitted to render it less incomplete. 
We stated originally that no resolution has ever been 
effected. This seems undoubted as to the grand mass.! 
The Earl of Rosse had indeed thought such development 
approaching with the 3-foot mirror, but only from an 
aspect presented also by the Dumb-bell and Ring nebule, 
since known to be gaseous; and the 6-foot giant broke 
down in its turn: and Newcomb has remarked that ‘‘in 
the most powerful telescopes the light fades away so 
softly and gradually that no such thing as resolution into 
stars seems possible. Indeed, it looks less resolvable 
and more like a gas in the largest telescopes than in 
those of moderate size.’ But there is less unanimity as 
to the two companions. Bond expressly states that 
under high powers 105 appeared to be a coarse cluster 
of stars. The 6-foot at Parsonstown on the contrary 
effected no such result; and we may remember that 
Bond had imagined momentary resolution in the Orion 
nebula. As to the bright ball, the Herschels and Bond 
lay no claim to success; the latter only remarking that 
the field preceding it contained multitudes of very small 
stars on a very even milky nebulous ground. Lord 
Rosse’s 3-foot gave it resolvable ; the 6-foot was silent. 
D’ Arrest once says, ‘nucleus stellatus circa medium” ; 
at other times finds a nucleus equalling a 9 or Io mag. 
star.2. It has been thought resolvable by Buffham, and I 
believe by Key, and has certainly that aspect in my 93- 
inch speculum. But even were these two companions 
found to be of a starry nature, their connection with the 
principal mass (though in the case of 105 supposed by 
Bond to be indicated by a line of stars) would yet remain 
to be demonstrated. It may be improbable, but it is not 
impossible, that each may be a case of mere optical 
juxtaposition. 
The telescope has comparatively failed. But the spec- 
troscope remains—an instrument as superior in analyti- 
cal as it is inferior in optical power. And here we get 
X It is very remarkable that the usually accurate Humboldt should have so 
misapprehended Bond’s meaning as to consider the 1500 stars scattered over 
the nebulous area as a proof of the resolution which he expressly disclaims. 
2 A similar appearance is so often ascribed in these beautiful observations 
to the centres of nebula, as to induce a suspicion of peculiarity, eizher c 
vision or of structure; in the latter case worthy of future attenticn. 
