satellites. He had seen, as he supposed, no less than six of these
bodies. As only two of these had been seen again, while two more were
discovered by Lassell, the inference was that Uranus has eight
satellites in all. These for a long time flourished in our text-books of
astronomy; and many writers, confident in the care and skill of Sir W.
Herschel, were unable for a long time to believe that he had been
deceived. Thus Admiral Smyth, in his 'Celestial Cycle,' wrote of those
who doubted the extra satellites:--'They must have but a meagre notion
of Sir W. Herschel's powerful means, his skill in their application, and
his method of deliberate procedure. So far from doubting there being six
satellites' (this was before Lassell had discovered the other two) 'it
is highly probable that there are still more.' Whewell, also, in his
'Bridgewater Treatise,' says, 'that though it no longer appears probable
that Uranus has a ring like Saturn, he has at least five satellites
which are visible to us, and we believe that the astronomer will hardly
deny that he' (Uranus, not the astronomer), 'may possibly have thousands
of smaller ones circulating about him.' But in this case Sir W.
Herschel, anxiously though he endeavoured to guard against the
possibility of error, was certainly mistaken. Uranus may, for anything
that is known to the contrary, have many small satellites circulating
about him, but he certainly has not four satellites (besides those
known) which could have been seen by Sir W. Herschel with the telescope
he employed. For the neighbourhood of the planet has been carefully
examined with telescopes of much greater power by observers who with
those telescopes have seen objects far fainter than the satellites
supposed to have been seen by the elder Herschel.
The third of the Herschelian myths was the lunar volcano in eruption,
which he supposed he had seen in progress in that part of the moon which
was not at the time illuminated by the sun's rays. He saw a bright
star-like point of light, which corresponded in position with the crater
of the lunar mountain Aristarchus. He inferred that a volcano was in
active eruption because the brightness of the point of light varied from
time to time, and also because he did not remember to have seen it
before under the same conditions. There is no doubt something very
remarkable in the way in which this part of the moon's surface shines
when not illumined by the sun. If it were always bright we should
conclude at once that the earth-light shining upon it rendered it
visible. For it must be remembered that the part of the moon which looks
dark (or seems wanting to the full disc) is illuminated by our earth,
shining in the sky of the moon as a disc thirteen times as large as that
of the moon we see, and with the same proportion of its disc sunlit as
is dark in the moon's disc. Thus when the moon is nearly new our earth
is shining in the lunar skies as a nearly full moon thirteen times as
large as ours. The light of this noble moon must illumine the moon's
surface much more brightly than a terrestrial landscape is illumined by
the full moon, and if any parts of her surface are very white they will
shine out from the surface around, just as the snow-covered peak of a
mountain shines out upon a moonlit night from among the darker hills and
dales and rocks and forests of the landscape. But Herschel considered
that the occasional brightness of the crater Aristarchus could not be
thus explained. The spot had been seen before the time of Herschel's
observations by Cassini and others. It has been seen since by Captain
Kater, Francis Baily, and many others. Dr. Maskelyne tells us that in
March 1794 it was seen by the naked eye by two persons.
Baily thus describes the appearance presented by this lunar crater on
December 22, 1835: 'Directed telescope to the moon, and pointing it to
the dark part in the vicinity of Aristarchus, soon saw the outline of
that mountain very distinctly, formed like an irregular nebula. Nearly
in the centre was a light resembling that of a star of the ninth or
tenth magnitude. It appeared by glimpses, but at times was brilliant,
and visible for several seconds together.'
There can be little doubt, however, that the apparent brightness of this
lunar crater, or rather of its summit, is due to some peculiar quality
in the surface, which may perhaps be covered by some crystalline or
vitreous matter poured out in the far distant time when the crater was
an active one. Prof. Shaler, who examined the crater when it was
illuminated only by earthshine, with the fine 15-inch telescope of the
Harvard Observatory (Cambridge U.S.), says that he has been able to
recognise nearly all the craters over 15 miles in diameter in the dark
part. 'There are several degrees of brightness,' he says, 'observable in
the different objects which shine out by the earth-light. This fact
probably explains the greater part of the perplexing statements
concerning the illumination of certain craters. It certainly accounts
for the volcanic activity which has so often been supposed to be
manifested by Aristarchus. Under the illumination by the earth-light
this is by far the brightest object on the dark part of the moon's face,
and is visible much longer and with poorer glasses than any other object
there.'
Here my record of astronomical myths must be brought to a close. It will
be noticed that in every instance either the illusion has affected the
actual observations of eminent and skilful astronomers, or has caused
such astronomers to put faith for a while in illusory observations. Had
I cared to include the mistakes which have been made by or have misled
observers of less experience, I could have filled many sheets for each
page of the present article. But it has seemed to me more instructive
to show how error may affect the observations even of the most careful
and deservedly eminent astronomers, how even the most cautious may be
for a time misled by the mistakes of inferior observers, especially when
the fact supposed to have been observed accords with preconceived
opinions.
XII.
_THE ORIGIN OF THE CONSTELLATION-FIGURES._
Although the strange figures which astronomers still allow to straggle
over their star maps no longer have any real scientific interest, they
still possess a certain charm, not only for the student of astronomy,
but for many who care little or nothing about astronomy as a science.
When I was giving a course of twelve lectures in Boston, America, a
person of considerable culture said to me, 'I wish you would lecture
about the constellations; I care little about the sun and moon and the
planets, and not much more about comets; but I have always felt great
interest in the Bears and Lions, the Chained and Chaired Ladies, King
Cepheus and the Rescuer Perseus, Orion, Ophiuchus, Hercules, and the
rest of the mythical and fanciful beings with which the old astronomers
peopled the heavens. I say with Carlyle, "Why does not some one teach me
the constellations, and make me at home in the starry heavens, which are
always overhead, and which I don't half know to this day."' We may
notice, too, that the poets by almost unanimous consent have recognised
the poetical aspect of the constellations, while they have found little
to say about subjects which belong especially to astronomy as a science.
Milton has indeed made an Archangel reason (not unskilfully for Milton's
day) about the Ptolemaic and Copernican systems, while Tennyson makes
frequent reference to astronomical theories. 'There sinks the nebulous
star we call the Sun, if that hypothesis of theirs be sound,' said Ida;
but she said no more, save 'let us down and rest,' as though the subject
were wearisome to her. Again, in the Palace of Art the soul of the poet
having built herself that 'great house so royal, rich, and wide,'
thither--
... when all the deep unsounded skies
Shuddered with silent stars, she clomb,
And as with optic glasses her keen eyes
Pierced through the mystic dome,
Regions of lucid matter taking forms,
Brushes of fire, hazy gleams,
Clusters and beds of worlds and beelike swarms
Of suns, and starry streams:
She saw the snowy poles of moonless Mars,
That marvellous round of milky light
Below Orion, and those double stars
Whereof the one more bright
Is circled by the other.
But the poet's soul so wearied of these astronomical researches that the
beautiful lines I have quoted disappeared (more's the pity) from the
second and all later editions. Such exceptions, indeed, prove the rule.
Poets have been chary in referring to astronomical researches and
results, full though these have been of unspeakable poetry; while from
the days of Homer to those of Tennyson, the constellations which
'garland the heavens' have always been favourite subjects of poetic
imagery.
It is not my present purpose, however, to discuss the poetic aspect of
the constellations. I propose to inquire how these singular figures
first found their way to the heavens, and, so far as facts are available
for the purpose, to determine the history and antiquity of some of the
more celebrated constellations.
Long before astronomy had any existence as a science men watched the
stars with wonder and reverence. Those orbs, seemingly countless--which
bespangle the dark robe of night--have a charm and beauty of their own
apart from the significance with which the science of astronomy has
invested them. The least fanciful mind is led to recognise on the
celestial concave the emblems of terrestrial objects, pictured with more
or less distinctness among the mysterious star-groupings. We can imagine
that long before the importance of the study of the stars was
recognised, men had begun to associate with certain star-groups the
names of familiar objects animate or inanimate. The flocks and herds
which the earliest observers of the heavens tended would suggest names
for certain sets of stars, and thus the Bull, the Ram, the Kids, would
appear in the heavens. Other groups would remind those early observers
of the animals from whom they had to guard their flocks, or of the
animals to whose vigilance they trusted for protection, and thus the
Bear, the Lion, and the Dogs would find their place among the stars. The
figures of men and horses, and of birds and fishes, would naturally
enough be recognised, nor would either the implements of husbandry, or
the weapons by which the huntsman secured his prey, remain unrepresented
among the star-groupings. And lastly, the altar on which the
first-fruits of harvest and vintage were presented, or the flesh of
lambs and goats consumed, would be figured among the innumerable
combinations which a fanciful eye can recognise among the orbs of
heaven.
In thus suggesting that the first observers of the heavens were
shepherds, huntsmen, and husbandmen, I am not advancing a theory on the
difficult questions connected with the origin of exact astronomy. The
first observations of the heavens were of necessity made by men who
depended for their subsistence on a familiarity with the progress and
vicissitudes of the seasons, and doubtless preceded by many ages the
study of astronomy as a science. And yet the observations made by those
early shepherds and hunters, unscientific though they must have been in
themselves, are full of interest to the student of modern exact
astronomy. The assertion may seem strange at first sight, but is
nevertheless strictly true, that if we could but learn with certainty
the names assigned to certain star-groups, before astronomy had any real
existence, we could deduce lessons of extreme importance from the rough
observations which suggested those old names. In these days, when
observations of such marvellous exactness are daily and nightly made,
when instruments capable of revealing the actual constitution of the
stars are employed, and observers are so numerous, it may seem strange
to attach any interest to the question whether half-savage races
recognised in such and such a star-group the likeness of a bear, or in
another group the semblance of a ship. But though we could learn more,
of course, from exacter observations, yet even such rough and imperfect
records would have their value. If we could be certain that in long-past
ages a star-group really resembled some known object, we should have in
the present resemblance of that group to the same object evidence of the
general constancy of stellar lustre, or if no resemblance could be
recognised we should have reason to doubt whether other suns (and
therefore our own sun) may not be liable to great changes.
The subject of the constellation-figures as first known is interesting
in other ways. For instance, it is full of interest to the antiquarian
(and most of us are to some degree antiquarians) as relating to the
most ancient of all human sciences. The same mental quality which causes
us to look with interest on the buildings raised in long-past ages, or
on the implements and weapons of antiquity, renders the thought
impressive that the stars which we see were gazed on perhaps not less
wonderingly in the very infancy of the human race. It is, again, a
subject full of interest to the chronologist to inquire in what era of
the world's history exact astronomy began, the moon was assigned her
twenty-eight zodiacal mansions, the sun his twelve zodiacal signs. It is
well known, indeed, that Newton himself did not disdain to study the
questions thus suggested; and the speculations of the ingenious Dupuis
found favour with the great mathematician Laplace.
Unfortunately, the evidence is not sufficiently exact to be very
trustworthy. In considering, for instance, the chronological inquiries
of Newton, one cannot but feel that the reliance placed by him on the
statements made by different writers is not justified by the nature of
those statements, which were for the most part vague in the extreme. We
owe many of them to poets who, knowing little of astronomy, mixed up the
phenomena of their own time with those which they found recorded in the
writings of astronomers. Some of the statements left by ancient writers
are indeed ludicrously incongruous; insomuch that Grotius not unjustly
said of the account of the constellations given by the poet Aratus, that
it could be assigned to no fixed epoch and to no fixed place. However,
this would not be the place to discuss details such as are involved in
exact inquiries. I have indicated some of these in an appendix to my
treatise on 'Saturn,' and others in the preface to my 'Gnomonic Star
Atlas'; but for the most part they do not admit very readily of familiar
description. Let us turn to less technical considerations, which
fortunately are in this case fully as much to the point as exact
inquiries, seeing that there is no real foundation for such inquiries in
any of the available evidence.
The first obvious feature of the old constellations is one which somehow
has not received the attention it deserves. It is as instructive as any
of those which have been made the subject of profound research.
There is a great space in the heavens over which none of the old
constellations extend, except the River Eridanus as now pictured, but we
do not know where this winding stream of stars was supposed by the old
observers to come to an end. This great space surrounds the southern
pole of the heavens, and thus shows that the first observers of the
stars were not acquainted with the constellations which can be seen only
from places far south of Chaldaea, Persia, Egypt, India, China, and
indeed of all the regions to which the invention of astronomy has been
assigned. Whatever the first astronomers were, however profound their
knowledge of astronomy may have been (as some imagine), they had
certainly not travelled far enough towards the south to know the
constellations around the southern pole. If they had been as well
acquainted with geography as some assert, if even any astronomer had
travelled as far south as the equator, we should certainly have had
pictured in the old star charts some constellations in that region of
the heavens wherein modern astronomers have placed the Octant, the Bird
of Paradise, the Sword-fish, the Flying-fish, Toucan, the Net, and other
uncelestial objects.
In passing I may note that this fact disposes most completely of a
theory lately advanced that the constellations were invented in the
southern hemisphere, and that thus is to be explained the ancient
tradition that the sun and stars have changed their courses. For though
all the northern constellations would have been more or less visible
from parts of the southern hemisphere near the equator, it is absurd to
suppose that a southern observer would leave untenanted a full fourth of
the heavens round the southern or visible pole, while carefully filling
up the space around the northern or unseen pole with incomplete
constellations whose northern unknown portions would include that pole.
Supposing it for a moment to be true, as a modern advocate of the
southern theory remarks, that 'one of the race migrating from one side
to the other of the equator would take his position from the sun, and
fancy he was facing the same way when he looked at it at noon, and so
would think the motion of the stars to have altered instead of his
having turned round,' the theory that astronomy was brought to us from
south of the equator cannot possibly be admitted in presence of that
enormous vacant region around the southern pole. I think, however, that,
apart from this, a race so profoundly ignorant as to suppose any such
thing, to imagine they were looking north when in reality they were
looking south, can hardly be regarded as the first founders of the
science of astronomy.
The great gap I have spoken of has long been recognised. But one
remarkable feature in its position has not, to the best of my
remembrance, been considered--the vacant space is eccentric with regard
to the southern pole of the heavens. The old constellations, the Altar,
the Centaur, and the ship Argo, extend within twenty degrees of the
pole, while the Southern Fish and the great sea-monster Cetus, which are
the southernmost constellations on the other side, do not reach within
some sixty degrees of the pole.
Of course, in saying that this peculiarity has not been considered, I am
not suggesting that it has not been noticed, or that its cause is in any
way doubtful or unknown. We know that the earth, besides whirling once a
day on its axis, and rushing on its mighty orbit around the sun
(spanning some 184,000,000 of miles) reels like a gigantic top, with a
motion so slow that 25,868 years are required for a single circuit of
the swaying axis around an imaginary line upright to the plane in which
the earth travels. And we know that in consequence of this reeling
motion the points of the heavens opposite the earth's poles necessarily
change. So that the southern pole, now eccentrically placed amid the
region where there were no constellations in old times, was once
differently situated. But the circumstance which seems to have been
overlooked is this, that by calculating backwards to the time when the
southern pole was in the centre of that vacant region, we have a much
better chance of finding the date (let us rather say the century) when
the older constellations were formed, than by any other process. We may
be sure not to be led very far astray; for we are not guided by one
constellation but by several, whereas all the other indications which
have been followed depend on the supposed ancient position of single
constellations. And then most of the other indications are such as might
very well have belonged to periods following long after the invention of
the constellations themselves. An astronomer might have ascertained, for
instance, that the sun in spring was in some particular part of the Ram
or of the Fishes, and later a poet like Aratus might describe that
relation (erroneously for his own epoch) as characteristic of one or
other constellation; but who is to assure us that the astronomer who
noted the relation correctly may not have made his observation many
hundreds of years after those constellations were invented? Whereas,
there was one period, and only one period, when the most southernmost of
the old constellations could have marked the limits of the region of sky
visible from some northern region. Thus, too, may we form some idea of
the latitude in which the first observers lived. For in high latitudes
the southernmost of the old constellations would not have been visible
at all, and in latitudes much lower than a certain latitude, presently
to be noted, these constellations would have ridden high above the
southern horizon, other star-groups showing below them which were not
included among the old constellations.
I have before me as I write a picture of the southern heavens, drawn by
myself, in which this vacant space--eccentric in position but circular
in shape--is shown. The centre lies close by the Lesser Magellanic
cloud--between the stars Kappa Toucani and Eta Hydri of our modern maps,
but much nearer to the last named. Near this spot, then, we may be sure,
lay the southern pole of the star-sphere when the old constellations, or
at least the southern ones, were invented. (If there had been
astronomers in the southern hemisphere Eta Hydri would certainly have
been their pole-star.)
Now it is a matter of no difficulty whatever to determine the epoch when
the southern pole of the heavens was thus placed.[57] Between 2100 and
2200 years before the Christian era the southern constellations had the
position described, the invisible southern pole lying at the centre of
the vacant space of the star-sphere--or rather of the space free from
constellations. It is noteworthy that for other reasons this period, or
rather a definite epoch within it, is indicated as that to which must be
referred the beginning of exact astronomy. Amongst others must be
mentioned this--that in the year 2170 B.C. _quam proxime_, the Pleiades
rose to their highest above the horizon at noon (or technically made
their noon culmination), at the spring equinox. We can readily
understand that to minds possessed with full faith in the influence of
the stars on the earth, this fact would have great significance. The
changes which are brought about at that season of the year, in reality,
of course, because of the gradual increase in the effect of the sun's
rays as he rises higher and higher above the celestial equator, would be
attributed, in part at least, to the remarkable star-cluster coming then
close by the sun on the heavens, though unseen. Thus we can readily
understand the reference in Job to the 'sweet influences of the
Pleiades.' Again at that same time, 2170 B.C. when the sun and the
Pleiades opened the year (with commencing spring) together, the star
Alpha of the Dragon, which was the pole-star of the period, had that
precise position with respect to the true pole of the heavens which is
indicated by the slope of the long passage extending downwards aslant
from the northern face of the Great Pyramid; that is to say, when due
north below the pole (or at what is technically called its sub-polar
meridional passage) the pole-star of the period shone directly down that
long passage, and I doubt not could be seen not only when it came to
that position during the night, but also when it came there during the
day-time.
But some other singular relations are to be noted in connection with the
particular epoch I have indicated.
It is tolerably clear that in imagining figures of certain objects in
the heavens, the early observers would not be apt to picture these
objects in unusual positions. A group of stars may form a figure so
closely resembling that of a familiar object that even a wrong position
would not prevent the resemblance from being noticed, as for instance
the 'Chair,' the 'Plough,' and so forth. But such cases are not
numerous; indeed, to say the truth, one must 'make believe a good deal'
to see resemblance between the star-groups and _most_ of the
constellation-figures, even under the most favourable conditions. When
there is no very close resemblance, as is the case with all the large
constellations, position must have counted for something in determining
the association between a star-group and a known object.
Now the constellations north of the equator assume so many and such
various positions that this special consideration does not apply very
forcibly to them. But those south of the equator are only seen above the
southern horizon, and change little in position during their progress
from east to west of the south point. The lower down they are the less
they change in position. And the very lowest--such as those were, for
instance, which I have been considering in determining the position of
the southern pole--are only fully visible when due south. They must,
then, in all probability, have stood upright or in their natural
position when so placed, for if they were not rightly placed then they
only were so when below the horizon and consequently invisible.
Let us, then, inquire what was the position of the southernmost
constellations when fully seen above the southern horizon at midnight.