342 
NATURE 
[ Fed. 9, 1882 
The negative or ambiguous results hitherto obtained do 
not preclude—-on the other hand they rather invite— 
attempts of a different kind. If again defeated, we are 
only where we were before. If in any measure successful, 
we may indeed find the mystery only increased by partial 
solution ; but such, after all, is the progress and the limit 
of all earthly knowledge. An obvious line of inquiry 
presents itself in the present instance, which seems not to 
have been adverted to in modern times—the possible 
evidence of variation either in form or brightness ; and 
the following notices, neither as exhaustive nor as minute 
as the subject would otherwise admit, have been chiefly 
put together with this view. 
The history of this nebula, which includes the ancient 
evidence, such as it is, of variation, is in brief as follows. 
The first mention of it, according to the late Prof. G. P. 
Bond, the eminent observer at Harvard College, Cam- 
bridge, U.S. America, to whose memoir we shall be in- 
debted for a considerable portion of our materials, occurs 
in an ancient star-catalogue with charts, supposed to date 
back as far as the close of the tenth century,! where it is 
represented of an oval form, Its previous omission in 
ancient catalogues is more easily accounted for than the 
remarkable silence of Tycho Brahe and Bayer. Marius 
(Mayer) in 1612 was the first to apply to it the recently 
invented telescope; his description of whitish rays, 
brightening to a dull and pallid centre, like a candle 
shining throug. horn, agrees sufficiently with its present 
aspect in a similar instrument. It again attracted notice 
in 1664, in consequence of the vicinity of a comet, for one 
of which bodies it has been several times mistaken, and 
it has never since been lost sight of, though Bouillaud 
thought its brightness variable between 1664 and 1666. 
In 1676 Kirch was of a similar opinion. Cassini in 1740 
described it somewhat unaccountably as nearly triangular. 
Mairan in 1754 endorsed the description of Marius. Le 
Gentil in 1749 observed it circular and of uniform 
density ; but oval, with central condensation, in 1757-58 ; 
and, from a consideration of all the known observations, 
believed it variable, without, however, being insensible to 
the differences arising from the inequality of optical 
means. Messier, on the other hand, whose familiarity 
with cometary phenomena rendered him a peculiarly 
competent witness, perceived no variation in a form 
similar to the present during the fifteen years ending in 
1771; and since that time none appears to have been 
suggested. In fact when we bear in mind the imperfec- 
tion of the ancient telescopes, and the known differences 
of vision and of judgment, by no means confined to earlier 
periods, we shall probably be of opinion that the evidence 
of change, though not to be rashly set aside, is far from 
amounting to demonstration. 
We must however pass on to more recent times. Sir 
W. Herschel described it in 1785 as 1$° long, and 16’ 
broad where narrowest ; his son in 1826 noted that its 
brightness, yradually augmenting from the oval circum- 
ference, receives a sudden increase at the centre, so as 
to form a nucleus, but without any distinct outline, of 10” 
or 12” in diameter. The whole light he describes as of 
the most perfectly milky and absolutely irresolvable 
character, without the slightest tendency to the flocculent 
appearance of the Great Nebula in Orion. Ten years 
afterwards Lamont, with the Munich refractor of 11°2 
(? English) inches, and a power of 1200, found the nucleus, 
of about 7”, longish in form, composed of very minute 
granulations, but without resolution. 
Thus matters stood till July, 1847, when, soon after its 
erection, the great Merz acbromatic of Harvard College 
was brought to bear upon it, with the confirmation of the 
almost star-like nucleus, but, owing no doubt to the un- 
favourable background of the summer sky, it was not till 
September 14 that the two dark rifts or canals were 
* The Persian astronomer Sf, Flammarion informs us, referred to it 
about the same period as a well-known object. 
detected, which form so strange and peculiar a feature in 
this grand object. But no resolution was attained. It 
was estimated that owing to the light and sharpness of 
| this admirable instrument upwards of 1500 stars were 
visible within the limits of the nebulosity, without the 
least apparent connection with it. And on which side 
they may lie who will presume to say? 
We may now give a reduction from the drawing of Prof. 
G. P. Bond, adequate to our present purpose, though, 
from the difference of material, far inferior in delicacy to 
the original steel engraving. Great pains were taken in 
delineation, and numerous measures were obtained from 
the divided circles of the instrument ; but an important 
admission of his must be borne in mind as to possible 
error in the comparative brightness of the different 
regions. 
The drawing includes, it will be observed, two bright 
patches, one on either side of the grand central mass, 
but each involved in its diffusion, and therefore presum- 
ably, though not demonstrably, a part of the same com- 
plex structure. The more distant one below to the left, 
or north-preceding (for our diagrams give the inverted or 
telescopic view), was discovered by Caroline Herschel in 
1783, and is known as HIV18, or No. 105 in the General 
Catalogue of Nebulz. The other attendant, pointed out 
by Le Gentil, No. 32 in Messier’s, 117 in the General 
Catalogue, is much smaller, but brighter, and of a cir- 
cularform. The interior canal is the longer and more dis- 
tinct, 14’ broad, very uniform for about halfa degree, with 
straight, sharp, and slightly diverging sides ; further north 
it begins to bend, and becomes fainter and less regular. 
The second is about 4’ distant from it, shorter, and less 
distinct, as occurring in fainter light. The two rifts are 
inclined at an angle of about 3°, opening towards the 
north, and their sides seem to have a common point of 
divergence ; and in several places along the course of 
the axis, which was distinctly marked, there were gather- 
ings of brighter knots and darker openings. 
We next give a copy, reduced to the same ‘scale, of a 
beautiful drawing with the same telescope by Trouvelot, 
in 1874; omitting, as unimportant for our present pur- 
pose, a large diffusion of faint nebulosity beyond the 
south extremity of Bond’s figure. Of this drawing, how- 
ever, itis expressly noted that it only gives a good gene- 
ral idea, and must be considered not as a map, but a 
picture. 
Lastly, we shall add a sketch obligingly made for the 
express purpose of this paper by the Rev. Jevon J. Mus- 
champ Perry, on December 14, 1881, with his great 18}- 
inch silvered glass reflector by Calver, an instrument 
of such perfection as to admit of not only separation, but 
measurement of that excessively difficult pair y* Andro- 
mede, the position of which Mr. Perry found, on De- 
cember 10, 1881, by two measurements with a power of 
600, 95° and 96°, with a distance of 0”°3.* It must be 
borne in mind that this is not, like Bond's and probably 
Trouvelot’s drawings, a combination of results, but a single 
sketch; according, however, precisely with one taken on 
a previous night, and it is no less material to add that 
subsequent examination in clearer air revealed, as might 
be expected from the light-grasp of such an instrument, 
a much greater extension of nebulosity in every direction, 
equal, as it would seem, to that shown in the American 
observations. 
In these two views taken with the same instrument 
after an interval of twenty-seven years, and a third six 
years later with a telescope of fairly equivalent power, 
we have before us the materials of an interesting com- 
parison. The general similarity is obvious ; but there are 
variations which it may not be well to ignore. One is, 
the form of the principal mass of light, spindle-shaped in 
* The agreement is remarkable, in so close an object, with one of th 
Washington measures, 1880°039, 95°°8, 0°35; their average for three year 
being 101°, 0°58. 
