36 
NATURE 
| Mov. 10, 1881 
THE AUTUMN SKY" 
Il. 
a attempt was made in a preceding paper to point 
out the most remarkable features of the planets that 
are at present so attractive for telescopic inquiry. We 
will now proceed to pass in review a few of the more in- 
teresting sidereal objects in that part of the heavens that 
is well placed for the observer. It is needless to say that 
within our limits nothing more can be expected than a 
very scanty selection, for the use of inexperienced students, 
of some of the most conspicuous of the many hundreds of 
double stars and nebule that are within the reach of 
ordinary instruments. We begin with the constellation 
Flercules, because it is rapidly gliding away from us, and 
the search for our first object should be undertaken as 
early as possible in the evening, especially if we are unac- 
quainted with its position. The possessors, of course, of 
equatorial mountings and divided circles wiil readily find 
anything in our selection from its assigned place ; but we 
propose to give such instructions as may be serviceable 
with altazimuth stands, aided by any common map, which 
will be occasionally supplemented by small diagrams. 
These, it must be borne in mind, correspond with a 
neridian position, and must be inclined one way or other 
to represent objects lying east or west of it. 
If then we wish to find without an equatorial, set to 
R.A. 16h. 37m., D.N. 36° 41’, the great globular cluster in 
the constellation Hercules, known as M(essier) 13, we 
must look out west-north-west for a Jarge triangle, nearly 
equilateral, of 3rd mag. stars B, 6, ¢, the left-hand angle of 
which at 8 is nearest the horizon ; at the other end of this 
side is ¢; if we continue the line 8 ¢ nearly as far again 
to the-right, bending a little upwards, we come upon a 
similar star n, and between ¢and 7, but rather nearer to 
the latter, our object is found. It is easily visible with 
the slightest telescopic aid, and discernible even without 
it in a clear dark sky. It will be instantly recognised as 
a round ball of misty light, which nearer the meridian 
would be of considerable brightness. It will not be 
favourably placed for examination; but those who have 
once caught sight of it will look out for it in a better 
position another year. At any time its resolution into 
stars will of course depend on the aperture; as this and 
the power are increased the mass will soon begin 
to sparkle, and the more brilliant points will rise out 
of the general haze; but it will require a large tele- 
scope to resolve it throughout. The great Copen- 
hagen achromatic of 11 inches aperture in the hands 
of d’Arrest effected it with a power of 95. Its com- 
ponents, ranging according to Sir J. Herschel from 
IO or II to I5 or 20 mags., must be thousands in 
number : his father had supposed 14,000. The state of 
compression, he observes, indicates not much greater 
density at the centre. Outliers surround it in streaky 
masses and lines ; and the ball, according to the Earl of 
Rosse, is intersected by three dark rifts confluent towards 
the centre, which I have perceived, as hnow objects, with 
my 93-inch mirror. This is unquestionably the finest 
specimen of a globular cluster visible in our latitudes; 
and even when the eye has recovered from its first sur- 
prise, it is never weary of reverting to this wonderful 
object. It may well be called wonderful, even at the 
distance at which we have to contemplate it. But 
imagination fails utterly to grasp the magnificence of 
such a scene, could we be transported to a standpoint 
two or three of its own diameters distant; or could we 
penetrate to the heart of the resplendent mystery, flaming 
on every side with suns innumerable, and where shade 
would be unknown and impossible. But are those 
thousands upon thousands suns indeed? We only know 
that they possess the solar character of intrinsic light ; 
yet that there is something peculiar in that light appears 
* Continued from p. to. 
by modern analysis, which finds the red end of their 
spectrum deficient ; but as to their nature, or their magni- 
tude, or their distance from us, or among themselves ; 
whether they were formed as they are, or have been 
gradually aggregated through innumerable ages—of all 
this we know absolutely nothing, and nothing are we ever 
likely to know. Nor if, as it is natural to suppose, gravi- 
tation is an inseparable property of matter, can we con- 
ceive how that glorious accumulation can be permanent, 
or escape ultimate transmutation into a fresh form of 
existence by the final coalescence of its members. It has 
indeed been supposed that, under certain admissions as 
to proportionate distance and velocity, such a mass might 
be preserved in a permanent condition of rotation; but 
we are treading here too closely upon the impossible, and 
though all may continue sensibly unvaried for ages, yet a 
secret principle must be at work that will issue in a final 
catastrophe—the opening, it may be, of a new and more 
glorious existence. We beings of a day can but confess 
our ignorance and our nothingness in the contemplation 
of such an evidence of creative power and uncompre- 
hended skill in what is but a minute speck to the keenest 
eye. 
We should not leave this object without noting its 
beautiful configuration in a large field with neighbouring 
stars; probably only an optical vicinity. Yet who after 
all can say which may be the nearest, now that it has 
been so clearly shown that there is but a precarious rela- 
tion between apparent magnitude and actual distance ? 
While we are in this region we should make an attempt 
to see another remarkable, though less-known, cluster, 
M 92, R.A. 17h. 13m., Decl. N. 43° 16.1 It may be found 
without circles, by patient sweeping some distance above, 
and to the left of, the last. Not equal in size to M 13, it 
is more compressed and more brilliant in the centre; 
“ formosissimus” in the Copenbagen telescope. It is a 
singular circumstance that its spectrum resembles that of 
M 13. 
Next, ever-charming Zyra, with its glowing sapphire, 
Wega, the beauty of the northern sky, whose minute 
II mag. attendant at about 46” is a well-known test for 
sensitiveness of vision. If this, as we are warranted in 
supposing, is a sun even more magnificent than our own, - 
a search fora planetary system might not be hopeless. 
Several observers have actually seen minute points in its 
immediate neighbourhood, but there is little agreement 
about them, and they remain for closer investigation. 
The accompanying diagram may serve to guide us to 
some other interesting objects here. Above Wega,a little 
to the left, are the two well-known pairs, e’, &, with the 
intervening debz/issima; long familiar to observers. It is 
no very uncommon feat, though one which I could never 
accomplish, to separate e! and e* at 3} distance with the 
naked eye ; the subdivision of the pairs, and the ruddier 
hue of one of the components of 1, will be apparent with 
a power of 50 or 60. There is of course an abstract 
possibility that this beautiful combination may be merely 
the result of coincident direction : but our optical sense 
revolts from the demand this would make upon it; and 
t This glorious object, discovered by Bode, is omitted in’ Sir J. Herschel’s 
Catalogue. 
