FIG. PAGE
A MEDIÆVAL ASTRONOMER. _From a painting by Gerard Dow_ 200
ASTRONOMY. _From a fresco in the Spanish Chapel
of Santa Maria Novella, Florence_ 217
38. The Half-Moon shape of the Habitable Earth (Ristoro) 247
CLIMATE MAP OF ABOUT A.D. 1110. _Reproduced from
Beazley’s Dawn of Modern Geography_ 248
39. Sun, Moon, and zenith. To illustrate _Par._ xxix 1-6 267
40. The Zodiac and the Months 276
41. The Ram on the Ecliptic. _From the Cosmi Historia
of Robert Flud_, A.D. 1612.
_Reproduced from Brown’s Aratos._ 279
MAP OF STARS VISIBLE BEFORE DAWN IN PURGATORY 295
42. Ursa Minor as a Horn. _Par._ xiii. 10 299
43. The Sun at the Equinox, seen from the poles and
the equator. _Conv._ III. v. 327
44. Lunar and Solar Eclipses 339
MAP OF THE WORLD BY HEINRICH OF MAINZ,
about A.D. 1110. _Reproduced from Beazley’s
Dawn of Modern Geography_ 344
45. The Universe of Dante 355
46. The Signs of the Zodiac at sunrise from the Mountain
of Purgatory 375
47. Northern Slope of the Mountain of Purgatory 377
48. Dante’s View of Earth from the stars. _Par._ xxii. 395
49. do. Six hours later. _Par._ xxvii. 396
50. An impossible interpretation of _Par._ xxvii. 399
51. The Rising Sun at the spring equinox. _Par._ i. 39 403
52. The Moon’s Epicycle and Deferent 449
53. Comparative sizes of the Sun and his satellites 490
ABBREVIATED TITLES OF BOOKS USED IN THE TEXT.
Dante’s Works:—
_Inf._ Inferno.
_Purg._ Purgatorio.
_Par._ Paradiso.
_Canz._ Canzone.
_Son._ Sonetto.
_Ball._ Ballata.
_Ecl._ Eclogue.
_V. N._ Vita Nuova.
_Conv._ Convivio.
_De Mon._ De Monarchia.
_V. E._ De Vulgari Eloquentia.
_Ep._ Epistola.
_Qu._ Quæstio de Aqua et Terra.
_El. Ast._ Elementa Astronomica (Alfraganus).
_Comp. del Mond._ Della Composizione del Mondo (Ristoro).
DANTE AND THE EARLY ASTRONOMERS.
INTRODUCTION.
In a beautiful passage of the _Convivio_ Dante describes how he first
began to devote himself diligently to science and philosophy. When
the gentle soul of Beatrice had passed to heaven, a great darkness
fell upon him: the streets of Florence were to him as a deserted city,
and his life empty and purposeless. It was long before he could find
any comfort, but at last he bethought himself of studying a book by
Boëthius, who when exiled, imprisoned, and unjustly condemned to death,
had strengthened his soul with the “Consolations of Philosophy.” This
led him on to Cicero’s book “On Friendship,” in which Lælius explains
how he is consoled for the death of Scipio.
Books in those days could only be had in manuscript, full of
abbreviations, and often also of errors, and at first the young
student found the Latin hard to master; but as he struggled on,
half deciphering and half divining the meaning, the mists cleared a
little, and the weight was lifted from brain and heart. With elation
he discovered that obscure passages were becoming luminous, and to
the exhilarating sense of conquest was added the joy of finding,
beautifully expressed, thoughts which had already floated in his own
mind, but dimly, as in a dream. He compares himself to one who, seeking
silver, should light (not without Divine guidance) on a treasure of
gold; for he found not only relief from his tears, but a door into a
new world of literature, philosophy, and science. Henceforth, he tells
us, he eagerly frequented the schools of the religious orders and the
discussions of the philosophers; and how extensive and thorough was his
learning we can see in his writings. In them we find a reflection of
thirteenth-century thought in every field of intellectual research.
Among all his studies was one which evidently had a great attraction
for him, even in the early days of the _Vita Nuova_, before learning
had become a passion. Astronomy appealed to many sides of his nature.
The beauty of the skies stirred his imagination; their suggestive
symbolism touched his religious sense; the harmony of the celestial
movements and the accuracy with which they can be foretold delighted
his instinct for order and precision. He must have read, and perhaps
possessed, some of the best text-books then available, and he grasped
with singular clearness the phenomena observed and the theories taught
in his day. His works are full of allusions to astronomy. In the _Vita
Nuova_ he finds pleasure in connecting the story of his lady with the
revolutions of the spheres; in the _Convivio_ he teaches the elements
of the science; in the Vision of the _Divine Comedy_ he journeys
through the universe as it was depicted by mediæval astronomers;
and throughout his works are scattered similes drawn from celestial
phenomena and descriptions of “le belle cose che porta il ciel.”[1]
------------------------------------------------------------------------
[1] “The fair things that Heaven holds.” Inferno XXXIV. 137, 138.
------------------------------------------------------------------------
Therefore, for full enjoyment and understanding of Dante’s works it is
necessary to have a rudimentary knowledge of astronomy.
Many of his readers think that Dante’s astronomy is very complicated
and difficult to understand. What makes it seem difficult is that in
this age we are generally unfamiliar with the skies. We do not eat our
breakfast or go to our office by the sun, nor do we watch the stars
to see when grouse-shooting begins or the summer holidays end. If it
is important for us to know at what hour the sun sets and lamps must
be lighted, or if we wish to see a view by moonlight, we consult an
almanac. When we think at all of the movements of the heavenly bodies,
our notions are usually taken from diagrams and tables, not from what
is actually seen in the skies. We only think, for instance, of the
seasons as caused by the earth’s journey round the sun, and the tilt
of her axis: therefore, when Dante speaks of Venus as a Morning Star
veiling the Fishes with her rays, or the horn of the Celestial Goat
touching the sun, it conveys little, although the seasons of spring
and of winter are as clearly indicated as if he had spoken of the
blossoming of primroses or the fall of snow. When Cacciaguida, in the
heaven of Mars, tells the date of his birth by counting how many times
the planet had since then returned to his Lion, those who only think of
Mars as circling round the Sun, and have never traced his path among
the stars, are at a loss, and think the method very far-fetched. A
short description, and especially a little individual watching, of the
apparent movements of the heavenly bodies, would put us in a position
to realize the meaning of a large number of Dante’s astronomical
descriptions and allusions, without any knowledge of any theory.
Others complain that the subject is dull. Dante’s astronomy, when
interpreted only by means of notes on single passages, is undoubtedly
dull—as dull as the history of his own times learned in the same way.
But when either subject is studied as a whole these passages acquire a
special interest; and they in their turn give new life to the subject
they illustrate.
Other readers say that Dante’s astronomy is so entirely false and
obsolete that it is not worth study. This is hardly true. Where Dante
speaks of appearances he is remarkably accurate, far more so than
most modern artists and writers of fiction. Where he speaks of the
heavens as he supposes them actually to exist, he is interpreting the
appearances according to the astronomical theories of his day, with
which he was very well acquainted. This interpretation was not correct,
but it was an ingenious and beautiful system, and very successful in so
far as it enabled astronomers to calculate the positions of sun, moon,
stars, and planets for any date. Its main outlines can be explained in
a few pages, with the help of a couple of diagrams, but when presented
thus, especially to those unfamiliar with the skies, it seems very
strange and artificial. To appreciate it at its true worth, we must
know just what are the phenomena it was intended to explain, and trace
its gradual development out of man’s first clear perception that the
movements of sun, moon, and stars follow unchanging laws.
The story of this development is of enthralling interest, and after
the system had been completed by one of the greatest mathematicians
the world has seen, its later history reads like a romance. Though of
classical Greek origin, it was almost wholly lost to Europe for many
centuries, it returned at last in Oriental dress, and its final form
was given by a devout and learned Dominican friar.
It was at this time that Dante was born, and the scholar-poet
immortalized the Ptolemaic system of astronomy in his verse, adding
to its popularity in his own day, and making it known to thousands of
readers since, who might otherwise scarcely have heard of it.
Dante’s astronomy, therefore, is of wide and deep significance. To
study its history is to learn a chapter in the development of the
human intellect; to see the universe with his eyes is to know how it
appeared, not only to his contemporaries but to men in many lands and
many centuries. The system of Ptolemy was already a thousand years
old when Dante studied it, and it continued to be taught long after
Copernicus had introduced a truer one; nor has it ever been completely
swept away, for much that it taught was accurate. The new astronomy
has developed from the old, and bears traces to this day, in its
phraseology, its written symbols, and its methods, of the many races
and ages which have contributed to its progress.
This book, therefore, is divided into two parts. In the first, I put
before my readers the elementary facts which form the foundations upon
which all astronomy is based, the movements of sun, moon, stars, and
planets, so far as they can be easily observed by the naked eye; then
follows a sketch of the attempts which were made to interpret these
observations from very early days until Dante’s time. Unnecessary
technicalities are avoided, but we shall try to enter into the thoughts
of past generations concerning the stars, to see why they were
interested, how they worked, what hindered and what helped them in
their search for truth.
In the second part, we shall examine Dante’s works, and see how
familiar he was with the movements of the skies, and how well he
understood the theories which in his time were held to explain them.
We shall see how astronomy was generally regarded in his day, what
books he read, and which authors influenced him most. We shall see how
false is the assertion often made that in the Middle Ages men studied
astronomy only for the sake of astrology, and how closely the science
of the stars was connected with religion and the loftiest speculations
of philosophy.
We shall also examine in particular some difficult passages connected
with astronomy which occur in Dante’s works, but my aim is not so much
to explain all the astronomical references as to put the reader in a
position to attempt an explanation himself.
My greatest ambition is to share with others the pleasure I have had in
learning what Dante knew and thought about the stars, and who were the
master builders who had erected through the ages the system so vividly
pictured in his immortal poem.
_FIRST PART._
THE STORY OF ASTRONOMY FROM PRIMITIVE TIMES
UNTIL THE AGE OF DANTE.
I. APPARENT MOVEMENTS OF THE HEAVENLY BODIES AS SEEN FROM EARTH.
The stars appear to us like points of light, differing greatly in
brightness, and scattered very irregularly over the dome above us. All
are moving, some much more quickly than others, yet a little attention
shows that they do not change their relative positions, and therefore
that all must share in one connected movement. If, for instance, any
one group be singled out, and looked for again some hours later, it
will be evident that it has moved considerably as a whole, yet the
stars composing it have kept the same places with regard to one another.
Careful and prolonged observations prove that to observers in the
northern hemisphere one star has hardly any perceptible movement, that
those nearest to it sweep round it in small circles, and those further
away in larger and larger circles, parts of which are hidden below
the horizon. All these circlings are performed in the same time, and
therefore the stars near the stationary point move more slowly in their
small circles than those further away.
All this is precisely what we should see if the sky were a great hollow
sphere, turning about the earth on an axis which runs close to the
almost stationary star—known therefore as the Pole Star. The direction
is from east to west, and a complete revolution is made in a day and
night.
We can plot the stars on a globe, and draw an equator on it, which will
everywhere be at an equal distance from the poles, and we may add other
circles, as on a terrestrial globe: then the position of each star can
be referred to these circles as towns on earth are found by latitude
and longitude, and the path of any moving body, such as a comet, may be
traced.
The stars fade out when the sun rises, but he too sweeps across the
sky as though carried round by the same sphere, and he sets like them,
in the west. Has he a fixed place on the sphere, keeping always the
same position relatively to the stars? No, for in the place where he
has just set we do not always see the same stars. Night after night
those which were clear in the western sky as soon as it was dark enough
to see them, grow closer to him, till at last they are lost in his
twilight beams. Thus the sun, though sharing in the daily east to west
movement, has a slow movement of his own on the sky-sphere, slipping
back from west to east, until in a year he has accomplished the whole
round, and sets again among the same stars.
Moreover, this peculiar movement of the sun is not a mere lagging
behind the stars, for his west to east motion is combined with a north
and south motion. If we note the star-groups which are just behind him
when he sets (or just before him when he rises), we shall find that
they form a great circle round the globe, half of which lies north
and half south of the celestial equator. The Greeks named this circle
the Zodiac, or “Path of the Animals,” because the star-groups forming
it were mostly called by the names of animals (the Ram, Lion, Fishes,
etc.). When the sun is in the most northerly part of the zodiac it is
summer in the northern hemisphere; when he is in the most southerly, it
is summer in the south. (See Map).
[Illustration: Fig. 1. The Sun’s path in the sky at different seasons.]
This north and south motion of the sun may be noted more directly in
another way. Seen from any given place on the earth, each star rises
and sets at the same points of the horizon always, and has the same
course in the sky; but the rising and setting points of the sun,
which on about the 21st of March are due east and west, travel daily
further north, and the sun mounts daily higher in northern skies until
about the 20th of June; then he returns towards the south, passing
the east and west points again about September 23, and reaches his
furthest point south about December 21. (The dates vary slightly
owing to Leap Year). The dates on which the sun reaches his furthest
north and furthest south points in this yearly journey are called the
“solstices,” because his motion seems to be checked, and he pauses or
“stands” before reversing his direction; the dates on which he passes
the midway point are the “equinoxes,” because at those points he is on
the equator, and makes day and night equal all over the earth.
The time taken by the sun to pass from one vernal (spring) equinox to
another is 365 days, 5 hours, 48 minutes, 45 seconds. Since this slow
motion along the zodiac is from west to east, contrary to the rapid
east to west motion which he shares with all the stars, he takes a
little longer to complete a daily revolution than they do; and if we
reckon a solar day as consisting of 24 hours, a “sidereal” (or star)
day is equal to 23 hours, 56 minutes, 4 seconds.
These are very elementary facts, but they are the fundamental facts
of astronomy, and without recollecting and holding them clearly in
mind we cannot understand Dante’s allusions, nor see the fitness of
any astronomical system, ancient or modern. To those who have only
read about astronomy in books, and have not watched the skies, they
may be puzzling, and I would beg these readers to make a few simple
observations for themselves, as this will help them more than any
written explanation can ever do to see the heavens with Dante’s eyes.
To appreciate the connected movement of the whole sky, some bright
stars near the Pole should first be watched, such as the Great Bear
and Cassiopeia, or for those in the southern hemisphere the Southern
Cross, Canopus, Achernar. Their motions should be compared with those
of bright stars near the equator, such as Orion, Virgo, or Aquila. The
constellations of the zodiac should be studied, and notes made of the
seasons at which each disappears in the rays of the sun.
The sun’s north and south movements can be easily recognized by noting
at what points of the horizon he rises or sets at different times of
the year; and the different heights to which he rises in the sky are
most simply observed by marking the length of the shadow of some tree
or pole at midday. Or if some rough kind of gnomon[2] be made, even
a flat piece of wood, laid on a sunny window-sill, with a long nail
driven vertically into it, the movement and varying length of the
shadow, from hour to hour, and from day to day, will make one realize
vividly the diurnal and the seasonal movement of the sun. This device,
in one form or another, was probably the first astronomical instrument
invented, and by its means ancient astronomers in many lands solved
important problems.
------------------------------------------------------------------------
[2] Greek _gnomon_, an interpreter. A pole set up in order to show the
length of shadow thrown by the sun.
------------------------------------------------------------------------
It is not necessary to explain that the daily apparent movements are
caused in reality by the earth’s rotation on her axis, and the yearly
apparent movements by her revolution round the sun. These are the
book-learned facts which for the most part obscure our perception of
the very things on which they are based. I would ask the reader to do
his best, for the moment, to forget them.
The movements of the moon among the stars are much more easily observed
than those of the sun, since we can see the stars at the same time, and
her revolution is much more rapid. She also is apparently carried round
with the daily east to west movement, and she also has a west to east
motion of her own, but so fast that it takes her round the star sphere
in one month, instead of one year. This revolution also takes place in
the zodiac. She is first visible as a fine crescent, just following
the sun, in the west, after he has set; next night she is markedly
further from the sun, on her eastward course, and is a larger crescent;
she continues increasing her distance from the sun and the size of her
disc, until, as full moon, she is rising in the east when the sun sets
opposite her in the west, and setting when the sun rises. After this,
she begins to wane, and, still travelling in the same direction, rises
later and later at night, and sets in the day; she draws gradually
nearer to the sun on the western side, till at last, as a fine crescent
with the horns turned in the other direction (_i.e._ always away from
the sun), she appears just before the rising sun in the east. Then for
a short time she is lost in his rays, till she emerges as a new moon on
the sunset side again.
[Illustration: Fig. 2. The Moon at Sunset.]
The moon completes a revolution among the stars in 27 days, 8 hours;
but it takes her a little longer to come up with the sun again, since
he has meanwhile been moving in the same direction along his yearly
path; and the ‘synodic’ month, or period from one new moon to the next,
is 29 days, 13 hours.
As well as the moving sun and the moving moon, there are five other
bodies, visible to the naked eye, which move among the stars. They look
like stars, but their movements would lead us rather to class them with
sun and moon. They also are in the zodiac, and they also, while carried
round with the universal movement from east to west, revolve slowly,
each in its own period, from west to east. But their motions are more
complicated than those of sun and moon. Two, which we call Venus and
Mercury, are never seen very far from the sun, and they oscillate
from side to side, sometimes appearing before him near sunrise, and
sometimes after him at sunset. Mercury keeps closest to the sun, and is
not so bright, and therefore less easy to see; but Venus is a brilliant
object when she gradually swings out further from the sun, remaining
longer each evening after sunset in the western sky. Then she gradually
draws back, closer to the sun, is lost in his rays, and a few days
after begins to appear on his other side, as a Morning Star, visible in
the east before sunrise. Here she swings out again, like a pendulum, to
her furthest distance west, and then draws in again, just as she did on
the sunset side of the sun.
In this way, swinging slowly from side to side of the sun, Mercury and
Venus make with him the circuit of the zodiac, completing a revolution
from west to east in about a year. The average period of Mercury’s
oscillation, counting, for instance, from one Greatest Western
Elongation (_i.e._ furthest distance from the sun on the west) to the
next, is 116 days; that of Venus is 584 days.
[Illustration: Fig. 3. The Path of Mars among the Stars, 1909.]
The other three “wandering stars”—or “planets,”[3] as they were named
by the ancient Greeks—Mars, Jupiter and Saturn, are also often seen as
morning or evening stars near the sun, but they do not always accompany
him, like Venus and Mercury. They may be seen at any distance from
him, even exactly opposite, so that they rise as he sets. They keep as
strictly to the zodiac, however, and travel in it from west to east, in
periods of approximately two, twelve, and thirty years respectively;
and their paths are also complicated by oscillations. Periodically
they slacken speed, stop, and go back a little distance among the
stars, then they slacken, stop, and advance again. These changes are
technically called direct motion, stations or stationary points, and
retrograde motion.
------------------------------------------------------------------------
[3] Greek _planetes_, a wanderer. This name was originally given to
Mercury, Venus, Mars, Jupiter, Saturn, and also to sun and moon, for
it indicated all the known heavenly bodies which changed their places
among the stars. In modern usage it is not applied to the sun, but only
to his satellites, of which many more are now known.
------------------------------------------------------------------------
It must have originally taken many years of patient watching to
discover and distinguish all these planets. In these days, by means of
an almanac and some knowledge of the constellations, they may easily be
found and traced. Mars and Venus move quickly during part of the time
they are visible, and if sketches be made of their positions among the
stars, and their paths marked for a few weeks, a very good idea may be
gained of the motions of planets as seen in the skies.
Once again, it is not necessary to explain here that these movements
of the planets are due partly to their revolution round the sun, and
partly to the Earth’s motion. Nor need we, for our present purpose,
consider them in any detail: all that is important to realize is the
general character of the movements, and their likeness to those of sun
and moon.
The distances, and therefore the sizes, of all the heavenly bodies are
completely beyond measurement, except with instruments and refined
methods; their physical nature could only be guessed at before the
discoveries of universal gravitation and spectrum analysis, in the 17th
and 19th centuries of our era. All that can be observed by naked eye
astronomy is difference of brightness and colour; as for instance the
contrast between ruddy Mars and white Jupiter; the steadier light of
all the planets as compared with stars; and the interesting fact that
the moon shines by reflected sunlight, which is made evident by the
connection between her phases and her position with regard to the sun.
Her surface, too, is clearly seen to be diversified by dark markings of
definite shape, but on no other body in all the sky can we make out the
least detail without a telescope.
The movements of the heavenly bodies, therefore, which still form one
of the most important parts of astronomy, were almost all that could be
studied by ancient astronomers, and gave them the only key they had to
the problems of the universe.
To sum up:—The chief apparent movements of the heavens, visible to the
naked eye, are eight, viz:—
The daily revolution of the entire heavens, carrying with it every
visible celestial body, in a little less than 24 hours; the revolutions
of sun, moon, and five naked eye planets, in seven different periods.
The first of these is from east to west, and is by far the most rapid.
The axis of revolution passes through two points which we call the
celestial poles, and the motion is parallel to the celestial equator.
All the others are in the main from west to east, though the progress
of the planets is complicated by periodical retrograde movements. All
take place in the zodiac, which is a series of constellations forming
a great band round the heavens. The path of the sun is a great circle
through this, called the Ecliptic (because eclipses can only happen
when the moon is also on it); and the paths of moon and planets are
slightly and variously inclined to it.
Thus the daily path of a star is affected only by the simple uniform
movement of the entire heaven (in reality the rotation of the Earth)
but the daily path of a planet, or of the sun or moon, results from a
combination of this general movement with its own peculiar movement,
which is generally in the opposite direction.
[Illustration: Fig. 4. The star sphere.]
If it is difficult to conceive a body moving simultaneously in two
different directions, an earthly analogy will make it easy. On a great
moving platform, such as that which encircled the Paris Exhibition in
1900, there are fixed posts etc. which revolve exactly as the whole
platform revolves and do not move about amongst themselves. These are
like the fixed stars on the (apparently) revolving sphere. But human
beings are free to add their own movements to that given them by the
platform on which they stand. One man turns his back and walks steadily
and very slowly in the opposite direction, and so he neutralizes part
of the platform movement and is not carried onward quite so quickly
as the stationary posts: he is the sun. A woman walks as he does, but
much more quickly, so that she rapidly passes many posts, although all
the time she is being carried backwards with them: she is the moon.
Children run backwards and forwards: they are the planets. Finally,
if all these people are also constantly crossing the platform slowly
from right to left and back again, their movements will be oblique to
the platform movement and will imitate the north and south movements of
sun, moon, and planets.
It is in this fashion that the movements of the skies present
themselves to careful observers on this seemingly stationary earth; and
in the youth of the world these apparent movements were believed to be
real. The ancients thought that the sky was actually revolving round a
steadfast earth, while the sun and moon and certain other “wandering
stars” had in addition various motions peculiar to themselves.
The table of periods which follows (see pp. 22-23) will be found useful
for occasional reference. Some of the terms used will be explained
later.
[Illustration: Fig. 5. Diagram illustrating Synodic and Sidereal
Periods.
The arrows show the direction of the Moon’s monthly
and the Sun’s yearly revolutions in the zodiac, as
seen from Earth.
When the Moon is opposite the Sun, for instance in
Libra while he is in Aries, she is full. In 27½
days she returns to the same place among the stars,
and this is a SIDEREAL MONTH. But the Sun
meanwhile has moved into Taurus, and not until the
Moon has reached Scorpio, opposite to him, will
she be full again, and complete her SYNODIC
MONTH (29½ days).]
REVOLUTIONS OF SUN, MOON, AND PLANETS
AS SEEN FROM THE EARTH.
_Days. Hrs. Mins. Secs._
Tropical Solar Year: period from one
vernal equinox to another, or from
one summer solstice to the next, &c. 365 5 48 45·5
(Our civil year is based on this).
Sidereal Year: period between two
successive returns of the sun to any
star on his path 365 6 9 8·9
The difference between these two kinds of year is due to Precession
of the Equinoxes, _vide infra_, p. 23.
_Days. Hrs. Mins. Secs._
Solar Day: period between two successive
passages of the sun across
the meridian (noon) — 24 0 0
Sidereal Day: period between two
successive passages of a star across
the meridian — 23 56 4
The difference between these two kinds of day is due to lag of the
sun behind the stars, his daily motion westward being slightly
retarded by his slow yearly motion eastward.
_Days. Hrs. Mins. Secs._
Mean Synodic Month: period between
two full moons 29 12 44 2·8
Mean Sidereal Month: period between
two successive returns of moon to
any star on her path 27 7 43 11·5
The difference between these two kinds of months is due to the fact
that while the moon is making her revolution among the stars, the
sun is also moving slowly on in the same direction.
_Days. Hrs. Mins. Secs._
Mean Anomalistic Month: period
between perigee and perigee
(_vide infra_) 27 13 18 37·4
PLANETS:—Mean Synodic Revolution: period
between two successive conjunctions with the sun,
and mean zodiacal revolution: period of revolution
round the zodiac.
_Mean Synodic Revolution. Mean Zodiacal Revolution._
Mercury 116 Days[4] 1·0 Years
Venus 584 ” 1·0 ”
Mars 780 ” 1·88 ”
Jupiter 399 ” 11·86 ”
Saturn 348 ” 29·46 ”
------------------------------------------------------------------------
[4] Fractions omitted.
------------------------------------------------------------------------
PRECESSION OF EQUINOXES: 50·25 seconds of arc
in one year; that is, 360 degrees (a revolution
among the stars of the zodiac) in 25,800 years
nearly.
_II. THE BEGINNINGS OF ASTRONOMY._
Note.
As these pages are passing through the press,
a letter from Mr. Maunder appears in _The
Observatory_ for August 1913 on “The Origin of
the Constellations,” and this should be consulted
by anyone interested in the subject. Mr. Maunder
points out that Ptolemy gives us much more precise
information than Aratus regarding the southern
limits of the ancient constellations, and that the
changes which he says he ventured to make in their
traditional forms are extremely insignificant.
Mr. Maunder further observes that the celestial
equator of Aratus cannot give any clue to the
origin of the constellations (as R. Brown
suggested), but only to the date of the work from
which Aratus copied, when some astronomer had drawn
the equator through the constellations. A slight
alteration of the text, Mr. Maunder says, would
give a correct equator for the date B.C.
1000.
See also Mr. and Mrs. Maunder’s article in _Monthly
Notices of the Royal Astronomical Society_ for
March 1904.
Proctor’s “Origin of the Constellation Figures” is
in his book _Myths and Marvels of Astronomy_.
II. THE BEGINNINGS OF ASTRONOMY.
The sky appears to us like an arch, embracing all our lives, Dante
says.[5] From the dawn of intelligence man must have recognized his
dependence upon the all-embracing heavens, especially the sun, without
which life would be impossible. The consciousness expressed itself in
many ways: in adoration of the sky, the sun, moon, and hosts of heaven;
in superstitious fear which regarded events on earth as directly
controlled by the heavenly bodies; in careful watching and recording of
their movements for useful purposes. Thus, long before astronomy became
an exact science, and was studied simply for its own sake, patient
observers had laid the foundations, and were familiar with many of the
movements we have been describing.
------------------------------------------------------------------------
[5] Conv. IV., xxiii. 56, 57.
------------------------------------------------------------------------
These are of great importance to primitive man. Sun, moon, and stars
are invaluable as guides, especially at sea, and we know that the
ancient Greek mariners used to steer their ships by observations of the
Great Bear, while the Phoenicians preferred to use the Little Bear for
this purpose. But the strongest and most universal incentive to careful
and prolonged study of the skies is our complete dependence upon them
for the measurement of time.
In the earliest period of their history, the Jews, the Greeks, and
probably every other nation, divided the day simply into morning,
noon, and evening, according as the sun was rising, or apparently
stationary, or sinking, with regard to the horizon; and the passage
of some bright stars indicated the time at night. But at a very early
period the first of all astronomical instruments was invented, by which
the sun’s varying height can be measured: hence the time of noon, the
dates of equinoxes and solstices, and the length of the solar year
can be determined. The gnomon in its simplest form is a pole set up
vertically on a smooth level surface, on which its shadow as cast by
the sun can be observed. The moment of shortest shadow marks the middle
of the day, the shortest midday shadow marks the summer solstice,
the longest the winter solstice, the equinoxes falling between. The
instrument also indicates the points of the compass, for the sun is
always due south in northern latitudes at midday: hence the Latin word
_meridies_ (French _midi_) means south as well as midday, and the
Meridian in astronomy is a line which passes through the north and
south points and the zenith, and is crossed by the sun at midday.
The gnomon was said to have been introduced into Greece by Anaximander
about 600 B.C., and the Babylonians claimed to be the inventors, but
it was probably invented independently by several races. The Chinese
certainly observed the length of the shadow more than two thousand
years B.C., and the very interesting fact has recently come to light
that a tribe in a hitherto unexplored part of Borneo use such an
instrument, invented by themselves. They set up a post about 6 ft.
high, and throw over the top a piece of string weighted at each end to
show when it is vertical; the length of the shadow cast by the post is
measured with a notched stick. By this means they tell the time of
day; and they also observe the sun (presumably with the gnomon) to know
the right season for planting their rice.[6]
------------------------------------------------------------------------
[6] Dr. C. Hose, in “Travel and Exploration,” for Feb. 1910, quoted in
“Nature,” Feb. 17, 1910.
------------------------------------------------------------------------
However rough the first gnomon may have been, its importance can
scarcely be overrated, for it introduced measurement and calculation
into observation of the sun’s movements, and it is the ancestor of our
modern sextants, transit telescopes, and other instruments of precision.
It was also the beginning of the sundial. The course followed by the
moving end of the shadow was traced on the ground, and divided into
equal parts: hence arose the custom which the Greeks adopted from
the Babylonians of counting twelve hours in every day, from sunrise
to sunset, and twelve hours in every night, from sunset to sunrise,
regardless of the varying lengths of day and night at different
seasons. This is known as the system of “temporary hours.” If we used
it in England, the twelve hours of a midsummer day would take twice as
long to pass as the twelve fleeting hours of a midsummer night; but in
Greece the inequality is much less, and in the latitudes of Babylonia
it is never striking. The skill and knowledge of the Greeks enabled
them, later on, to construct dials of different kinds, which marked
“equal hours,” such as we use now; but the system of “temporary hours”
did not altogether die out till after the invention of pendulum clocks
in the 17th century of our era.
Clepsydras, or water-clocks, were also used in Egypt and Babylonia,
and ancient Greece; and there is still a large one in Canton, where
a reservoir is placed in a tower, and the water falling, drop by
drop, into a receiver whose depth is marked in figures on the wall,
indicates the passing of time just as sand does in running through an
hour-glass. These clocks cannot have kept very good time, however, or
they would have been more used by the Babylonian and Greek astronomers
who took pains to ascertain the exact positions of the stars. Owing to
the diurnal revolution of the skies, the time at which any celestial
body rises or crosses the meridian after another is an index of their
distance apart, east and west on the sphere, and this is how it is
reckoned by modern astronomers. But the ancients seem to have been
never able to trust their clepsydras sufficiently to use this method,
and only referred to them for approximate time.
The gnomon, valuable as it is for marking the sun’s daily course, and
the north and south part of his yearly motion, is a limited instrument.
It cannot show his westerly motion on the sphere, nor is it of any use
for the planets. To trace these motions, and the monthly journey of
the moon, the first step is to distinguish the stars, by grouping and
naming them, especially those which lie in the path of sun, moon, and
planets. The invention of some kind of zodiac is probably older even
than the invention of the gnomon, and also originated independently
among different races. The germ of the idea may be found to-day among
races low in the scale of civilization. The Australian aborigines are
familiar with that unique star-cluster which we call the Pleiades,
and know that its appearances and disappearances are periodical and
coincide with the seasons. A Queensland tribe, for instance, has
a legend in which the stars figure as six sisters who have been
transported to the skies, and it is said that they sometimes appear
before the sun in order to throw down icicles, an evident allusion
to the fact that the Pleiades begin to appear just before sunrise in
May, the Australian winter. The natives of Tahiti divide their year
into “Matarii i nia” and “Matarii i raro,” which means Pleiades Above
and Pleiades Below (_i.e._ the horizon at the beginning of night). Sir
Norman Lockyer has shown that the mysterious alignments of stones found
at Stonehenge, Carnac, and other places, may have been so arranged
in order to show the direction, some of the sun at his rising on
certain dates, notably the morning of the summer solstice, and some
of the Pleiades or other striking stars, whose rising just before the
sun would enable ancient astronomers to fix the dates of important
festivals.
Such observations as these, of which many instances might be drawn from
many parts of the world, are first steps towards studying the whole
path of the sun through the stars, and of forming a calendar with a
name or number for every day in the year. Until the stars are known,
and a calendar fixed, the motions of sun and moon cannot be learned
in detail, the planets can scarcely be distinguished from the stars
and from one another, and there are no settled dates from which to
calculate their periods.
The first zodiac of which we have written record is a lunar one of
28 constellations, which is referred to in the “Canon of the Emperor
Yaou,” a Chinese emperor who began to reign in B.C. 2356. “Yaou
commanded He and Ho, in reverend accordance with their observation
of the wide heavens, to calculate and delineate the movements and
appearances of the sun, the moon, the stars, and the zodiacal spaces,
and so to deliver respectfully the seasons to the people.” That these
astronomers studied “the movements and appearances” of the sun by
means of the gnomon as well as observations of the stars is plain from
what follows, where directions are given for determining the solstices.
One astronomer was commanded by the Emperor to “reside at Nankeaou and
arrange the transformations of the summer, and respectfully to observe
the extreme limit of the shadow. The day, he said, is at its longest,
and the star is _Ho_: you may thus exactly determine midsummer.” _Ho_
(= fire) is the fiery red Antares in Scorpio. The star of the winter
solstice, when “the day is at its shortest” was Maou, which is the
Pleiades. Directions are also given for observing the spring and autumn
equinoxes, when day and night are of medium length, and certain other
stars are to be observed.[7]
------------------------------------------------------------------------
[7] Journal of the British Astronomical Association, June 24, 1909,
report of a lecture on Chinese astronomy by E. B. Knobel, F.R.A.S.
------------------------------------------------------------------------
The Hindus had also a lunar Zodiac, but with only 27 constellations,
and the Arabs had their 28 “Mansions of the Moon.” These 27 or 28
asterisms were evidently suggested by the moon’s sidereal period of 27¼
days. But her synodical period, _i.e._ her revolution with regard to
the sun, in which she runs through her phases, is much more convenient
for marking a period of time for general uses, and this month of about
30 days has been almost universally adopted by primitive peoples, the
first day being counted when the crescent new moon begins to be seen
after sunset. From this custom arose another, that of counting the
beginning of the day from sunset, but in various times and places other
starting-points have been chosen—sunrise, midday, or midnight.
Twelve of these synodical lunar months are nearly equal to one solar
year, and this doubtless suggested the solar zodiac of twelve
constellations, each constellation marking the portion of sky passed
over by the sun in a month. The Chinese “Yellow Path of the Sun”
contained twelve animals, the Mouse, Cow, Tiger, Rabbit, Dragon,
Serpent, Horse, Ram, Ape, Hen, Dog, and Pig. These animals were widely
adopted by other nations—the Koreans and the Japanese, the Mongols of
Tibet, the Tartars, and the Turks.
Another zodiac, however, was destined to have an even wider popularity,
spreading, in the course of centuries, from Greece to Arabia,
Persia, India, and China, where it finally superseded the native
constellations; it crossed the Mediterranean into Africa, conquered the
whole of Europe, and is used to-day over the whole civilised world.
The names of these twelve zodiacal constellations are familiar to us
all:—
_English Names. Latin Names._
Ram Aries
Bull Taurus
Twins Gemini
Crab Cancer
Lion Leo
Virgin Virgo
Scales Libra
Scorpion Scorpio
Archer Sagittarius
Capricorn Capricornus
Water-Bearer Aquarius
Fishes Pisces.
Strange to say, we cannot tell with any certainty where, when, or by
whom, this ancient series of constellations was devised and named. The
earliest full description which we possess is by a Greek poet of the
4th century B.C., Aratus. A line from the prologue to his “Phenomena”
was quoted by St. Paul in his address to the Athenians on Mars’ Hill.
“From Zeus we lead the strain, he whom mankind
Ne’er leave unhymned; of Zeus all public ways,
All haunts of men are full, and full the sea
And harbours; and of Zeus all stand in need.
We are his offspring;[8] and he, mild to man,
Gives favouring signs and rouses us to toil,
Calling to mind life’s wants; when clods are best
For plough and mattock, when the time is ripe
For planting vines and sowing seeds he tells.
Since he himself hath fixed in heaven these signs,
The stars dividing; and throughout the year
Stars he provides to indicate to men
The seasons’ course, that all things duly grow.”[9]
------------------------------------------------------------------------
[8] Acts, xvii. 28.
[9] _The Phainomena of Aratos, done into English verse by Robert
Brown_, lines 1-13.
------------------------------------------------------------------------
But Aratus did not know who had invented the names of the star-groups
which he describes. “Some man of yore,” he supposes,
“A nomenclature thought of and devised,
And forms sufficient found. For men could not
Or tell or learn the separate names of all,
Since everywhere are many, size and tint
Of multitudes the same, but all are drawn around.
So thought he good to make the stellar groups,
That each by other lying orderly,
They might display their forms. And thus the stars
At once took names and rise familiar now.”[10]
------------------------------------------------------------------------
[10] _Ibid._, 373-382.
------------------------------------------------------------------------
It is, to say the least, exceedingly doubtful, whether the naming of
star-groups was so promptly carried out by one individual, especially
as Aratus’ poem includes, besides the twelve zodiacal constellations,
thirty-six others, which contain all the bright stars of the sky
except those too far south to be seen in the temperate regions of
our northern hemisphere. The spaces thus left blank were afterwards
filled up, chiefly in the 17th and 18th centuries of our era, and the
regions round the South Pole are now crowded with a mixture of birds
and scientific instruments; but the names and the figures of the
traditional forty-eight constellations still find undisputed places on
our globes and star-maps.
Some of these figures are very strange and suggestive. We have a maiden
with wings, a centaur shooting arrows, a flying horse, a water-snake
with a crow and a cup on its back, a charioteer with a goat on his
shoulder, a man strangling a serpent, another pouring water into the
mouth of a fish, and a strange beast like a goat with a fish’s tail.
All had their meaning, doubtless, to their originators, but to us
they are cryptic characters, hard to decipher. Among the zodiacal
constellations only one is obvious, Libra the Scales, the sign in which
the sun is when days and nights are perfectly balanced in length; but
this is comparatively recent, for Aratus and his contemporaries give
in its place the Claws of the Scorpion, the latter being an enormous
monster extending over the space of two asterisms. The figures may have
been religious symbols, or an illustration of some myth concerning
the sun’s yearly course, or each of the twelve may have indicated the
weather or the occupation suitable to the month it represented. The
ear of corn in the hand of the Virgin, and the juxtaposition of three
watery figures in Capricornus, Aquarius, and Pisces, suggest the latter
explanation. Many different ideas probably played a part in the origin
of these mysterious constellation-forms. The Greeks, and after them the
Romans, when adopting the old constellations, sometimes adopted also
the old myths which still clung about them; sometimes they ascribed
legends to them from their own mythology. Thus, the kneeling figure
with his foot upon a dragon, became and remains the hero Hercules,
although Aratus only describes him as a man toiling at some unknown
task, and says he is called simply the Kneeler. Successive generations
of astronomers altered some of the figures, but probably only to a
slight extent.[11]
------------------------------------------------------------------------
[11] Ptolemy says he made a few changes, as his predecessors had done.
(Delambre, _Histoire de l’Astronomie Ancienne_, ii. 261).
------------------------------------------------------------------------
The poem of Aratus enjoyed an immense popularity in classical times
and throughout the Middle Ages, and no doubt helped to stereotype the
forms whose origin was already forgotten when he wrote. He was not
an astronomer, however, and the poem is only a popular paraphrase of
a lost work by Eudoxus. This Greek astronomer had lived a hundred
years earlier, and it is thought that he himself copied from an older
source. The attempt to discover this source has been the object of
many ingenious conjectures, and much research among ancient monuments
and writings. Some of the old constellations are met with in Isaiah
and Job, in Homer, on tablets found at Nineveh, and an immense
antiquity is sometimes claimed for them. Dupuis, writing at the end of
the eighteenth century, thought he had conclusively proved that the
figures of the zodiac were designed in Egypt 15,000 years ago![12] Miss
Plunkett, in her “Ancient Calendars and Constellations” assigns them to
the seventh millenium before Christ.
------------------------------------------------------------------------
[12] _Origine de tous les cultes, ou Religion universelle_, by C. F.
Dupuis.
------------------------------------------------------------------------
[Illustration: THE OLD CONSTELLATION FIGURES.
SOUTHERN HEMISPHERE.]
[Illustration: NORTHERN HEMISPHERE.
THE OLD CONSTELLATION FIGURES ACCORDING TO ARATUS.
_In Ptolemy’s Catalogue Equuleus and Corona Australis are added to
these._
_(From Peck’s “Constellations and How to Find Them.”)_]
An ingenious theory, suggested independently by Schwartz and Proctor,
and developed by Mr. E. W. Maunder,[13] is founded on an examination
of the space round the South Pole which was left blank by the ancient
constellation designers. From its extent, Proctor concluded that they
cannot have seen further south than about 40° from the South Pole, and
therefore that they must have lived in a latitude of about 40° north of
the equator (say, central Asia or Asia Minor); from the position of its
centre, which must have been the Pole, he concluded that the date was
about B.C. 2200. For the centre of the circular patch seems to lie near
the star _Delta Hydri_, which was the South Pole star at that time.
(This movement of the Pole among the stars, due to “precession,” will
be explained later). This date does not differ much from that found
by Robert Brown, from the position of the celestial equator among the
stars, as described by Aratus; he says B.C. 2084.[14] Schwartz gave
B.C. 1400; Mr. Maunder, from additional considerations of the positions
of various constellation figures, says that they must all have been
originally designed about B.C. 2800.
------------------------------------------------------------------------
[13] _Journal of the British Astronomical Association_, “The Oldest
Astronomy,” July 1898, June 1899, April 1904, May 1909; _The
Observatory_, December 1898; _Knowledge_, October 1904; and elsewhere.
[14] _The Phainomena of Aratos_, by Robert Brown. See also his
_Eridanus, River and Constellation_; _Primitive Constellations_, and
other works.
------------------------------------------------------------------------
Unfortunately the descriptions of Aratus are neither very
precise nor consistent with one another, and he is our oldest and
our main authority for the forms and positions of the ancient
constellations.[15] It may, however, be taken as practically certain
that they had been designed many centuries before he wrote, and that
the Greeks received them from the Babylonians. Orion and the Pleiades,
the Great Bear and Arcturus, and perhaps many others, were familiarly
known in the Levant as early as the tenth century before Christ; and we
find traces of our zodiac, or its beginnings, in Babylonia at least as
early as the eleventh. It is always to Egyptians and Babylonians that
the Greeks referred as their predecessors and teachers in astronomy,
but the native constellations of Egypt seem to have been different, and
so far as we know at present the Babylonians began earlier and made
greater progress in star-lore than any other nation before Greece.
The latest results of expert investigation of astronomical tablets
discovered in the ancient clay libraries of Babylonia and Assyria,
tend to show that astronomy was of native growth there, and developed
very slowly.[16] Star-worship and the need for a calendar led their
inhabitants to observe the skies thousands of years ago; but their
early work was naturally vague and rude.
------------------------------------------------------------------------
[15] We are not sure what limits Aratus intended to set in the south
to Centaur and Argo, and notably to the River Eridanus, which used to
flow beneath the Sea-Monster (Cetus), joining the Water poured out
by Aquarius. It changed its bed (like the Euphrates, of which it is
perhaps the heavenly counterpart), and now has left the Sea-Monster
high and dry, while on its ancient banks a chemist’s furnace and a
sculptor’s workshop have been set up.
The Celestial Equator of Aratus fails to agree with the Equator of B.C.
2084, not only in passing over the head of Orion, instead of through
his belt, as Brown himself points out, but also in running through
the eye of the Bull, instead of his “crouching legs alone,” so this
part is altogether too far north. The Equator some 1200 years later
agreed better here, and equally well elsewhere, except in the opposite
part of the sky where it was then too northerly for Aratus, leaving
Corvus to the south of the line. Much the same may be said about the
tropical circles. Either Aratus was careless, or the globe from which
he took his descriptions was incorrect: in any case, there results an
uncertainty of many centuries and many degrees in date and latitude.
[16] Epping and Strassmeier, _Astronomisches aus Babylon_, Kugler’s
_Babylonische Mondrechnung_, and _Babylonische Sternkunde_.
Schiaparelli’s two monographs on Babylonian Astronomy, from which much
of the information here given is derived, are chiefly based on these
works.
------------------------------------------------------------------------
This star-worship and star-study seems to have been learned by the
Semitic Babylonians, and their descendants and rivals the Assyrians,
from a race with whom they met and mingled in the grey dawn of history,
but whose existence was unknown to us before the middle of last
century.
[Illustration: The Moon-God of Ur. [_To face p. 36._
From a cylinder-seal in the British Museum, dated about B.C. 2400.
Reproduced by permission of the Trustees.]
[Illustration: Fig. 6. The triple star-sign of the Babylonians.]
This people, who belonged to a totally distinct family of nations, and
are known to us now as Sumerians, had settled near the mouth of the
Persian Gulf, when it ran further inland than it does now, and more
than five thousand years ago used a kind of writing on soft stones
(later, on bricks) which had obviously arisen from some form of picture
writing, and ultimately developed into cuneiform. Their reverence
for the heavenly bodies is shown by the fact that the familiar star
sign, [star sign] which appears on very early Sumerian inscriptions,
denotes their word for god or lord, and on the monuments of Babylonia
and Assyria we meet constantly the triple sign This, we learn from
the inscriptions, stood for three great deities, the Moon-god, the
Sun-god, and the goddess of the planet Venus. Our illustration shows an
inscription in early Babylonian script, and a scene which represents
the vassal of a king of Ur (Abraham’s “Ur of the Chaldees”) being
led into the presence of the Moon-god.[17] It is believed to date
from about B.C. 2400. The Babylonians were an intensely superstitious
people, and a large part of their omens were drawn from observations of
the skies. Every city from this period onward had its ziggurat or great
tower formed of several superimposed cubes, usually seven in number,
diminishing in size and probably crowned by the shrine of the local
deity. It is not certain what purposes were served by these towers,
but the successive platforms may well have been the observatories from
which the Babylonian priests, gazing through the clear air and over
the level plains, watched, year after year, and century after century,
eclipses of sun and moon, risings and settings of stars and planets,
and all the changing pageant of the skies, which to them were eloquent
of peace and prosperity, or of war and misfortunes in their land.
------------------------------------------------------------------------
[17] King, History of Sumer and Akkad, p. 246.
------------------------------------------------------------------------
Although this illusory art chiefly occupied the early Babylonian
astronomers, they made some observations of real value, and gradually
acquired true knowledge concerning the movements of the heavenly bodies.
Tablets a few centuries older than the Chinese _Canon of Yaou_
containing lists of the Sumerian names of twelve months, show that
this people had established a luni-solar year. Fortunately for the
progress of astronomy the year does not contain an exact number of
months, or even of days: at the end of twelve lunar months, a few
more days and hours must elapse before the sun has returned to his
original place among the stars, and before the round of the seasons is
completed. Therefore the first rough approximation had to be constantly
corrected if calendar festivals were to recur at the same seasons; and
thus the priests, who in early times were usually the calendar makers
and keepers, became gradually better and better acquainted with the
movements of sun and moon, and the appearance of star-groups. It is
interesting to compare the different ways in which various races have
solved the problem of calendar-formation.
The Chinese had a year of twelve months, and added an intercalary month
occasionally, in such a way that the average length of the year was
brought up to 366 days. The written character for “intercalary” in
both Chinese and Japanese is a compound of the characters for “gate”
and “Emperor,” because in ancient days the Emperor used to perform the
ceremonies proper to each of the twelve months in the special room of
his palace dedicated to that month, but in the intercalary month he
performed them in the doorway of the palace.
The Egyptians and the Arabs seem to have given up the attempt to
harmonize the two periods, though both of these nations reckoned twelve
months in their years. The Egyptians counted thirty days to each month,
and added five days more at the end of the twelfth, so that the months
can have had no connection with the moon: the year had, in fact, been
calculated from the position of the sun among the stars, beginning
with the morning on which Sirius rose just before it. This “heliacal
rising” of Sirius heralded the great event of their year, the overflow
of the Nile. The Arab year, on the contrary, was purely lunar, for
it consisted of twelve months which were alternately of twenty-nine
and thirty days: they therefore corresponded pretty closely with the
moon’s phases, but had no connection with the sun or the seasons. The
Mahomedans still use this lunar year.
The new moon festivals of the Hebrews prove that the moon was important
to their calendar, but the three chief feasts of First-fruits, of
Ingathering, and of the Passover, were so closely connected with
the seasons that their year must have been luni-solar. It consisted
of twelve months, one of which was sometimes doubled, but how they
decided when this was necessary is nowhere described in the Old
Testament. Some think, that as an offering of first-fruits was to be
made on a certain day of a certain month, the month preceding it was
doubled in every year in which it was evident that the crops would
not be far enough advanced for the first-fruits to be gathered so
soon: in this way no direct observations had to be made of the sun’s
movements, but the year was accommodated to them by observations of the
seasons.[18]
------------------------------------------------------------------------
[18] Schiaparelli, _L’ Astronomia nell’ Antico Testamento_, chap. vii.;
Wellhausen, _History of Israel_, chap. iii.
------------------------------------------------------------------------
The Babylonian calendar is the most interesting of all, for it was the
most intimately connected with star-observation. At first an extra
month seems to have been added to the usual twelve, in an irregular
way, whenever found necessary, judging by a tablet of the great king
Hammurabi, who united all the cities of southern Babylonia under one
rule, and gave them the famous Code of Laws, communicated to him by the
Sun-god. The tablet runs as follows:—
“Thus saith Hammurabi: the year having gone wrong,
let the coming month be registered by the name of
Ululu the second. And instead of the payment of
taxes being made on the 25th day of Tasritsu, let
it be made on the 25th day of Ululu the second.”
Hammurabi reigned about B.C. 2200. A thousand years or more after
this, we find that royal decrees for correcting the calendar were
never necessary, for the astronomers had invented more than one system
for keeping the year right. One of these was to observe, like the
Egyptians, the heliacal rising of certain stars. The little group of
three stars in the head of the Ram, which we call Alpha, Beta, and
Gamma Arietis, was found very convenient for this purpose. When it
rose just before the sun in the month Nisan, the observers knew that
all the twelve months would fall in their right seasons, but when it
remained invisible (hidden in the morning twilight) until the following
month, the calendar was evidently running ahead of the sun, and that
year was lengthened by adding a thirteenth month. This is the meaning
of the directions given on a tablet now in the British Museum:—
“The asterism Dilgan[19] rises heliacally in the
month of Nisan. Whenever this asterism remains
invisible, let its month be forgotten,”
------------------------------------------------------------------------
[19] Sayce and Bosanquet identify Dilgan with Capella, not with
part of Aries, and consider that a date of about B.C. 2000 is
indicated—(_Monthly Notices_ xxxix, 454). But in any case the method of
calendar formation is the same.
------------------------------------------------------------------------
that is, let it be taken over again, as if it had not already been
counted. Similar directions are given for some other asterisms and
their corresponding months. But a second method, which was peculiar,
so far as we know, to the Babylonians, was that of using the moon as
a pointer to indicate the place of the sun. Whereas the sun’s place
among the stars can only be inferred, the moon’s can be plainly seen,
and her phase indicates her distance from the sun at any time. A tablet
of unknown date, belonging to the last millenium before our era, or a
little earlier, gives the following directions:—
“When on the first day of the month of Nisan the
asterism Mulmul (the Pleiades)[20] and the Moon are
seen together, the year will be normal. When on the
third day of Nisan the asterism Mulmul and the Moon
are together, the year will be full” (that is, will
contain 13 months).
------------------------------------------------------------------------
[20] Sayce and Bosanquet understand Capella here also.
------------------------------------------------------------------------
Each Babylonian month began when the new moon was first visible after
sunset; if at this moment she was seen with the Pleiades, it is clear
that the sun, which had just set, was not far west of the cluster; if
however, it was not till the moon was three days old that she was seen
with the Pleiades, she would then be some distance above the horizon at
sunset: consequently the sun was some distance west of the Pleiades.
In this case he would also be west of Dilgan, the Ram’s Head, so those
stars would rise after him in the morning, and be hidden in his light:
therefore, both the morning and the evening observation combined to
show that his course was not completed, and that the year must be
lengthened by the addition of an extra month.
[Illustration: Fig. 7. First Year, normal. New Moon near the Pleiades
after sunset on the 1st of Nisan.
The position of the young moon (which always
closely follows the sun) showed that the sun was
not far west of the Pleiades; and about 1000
B.C. this proved that it was near the
vernal equinox. The sun’s position is given for
about half an hour after sunset, when the Pleiades
would first be visible.]
[Illustration: Fig. 8. Second Year, normal. New Moon not far from
Pleiades on the 1st of Nisan.
It takes the sun 365 days to return to the same
place among the stars, but the Babylonian year of
12 lunar months (each of 29 or 30 days) was 11 days
short of this: therefore on the 1st of Nisan in
this year the sun had still 11 days’ march before
him ere he returned to the position of Fig. 7. This
is equal to about 11°, so the young moon was also
about 11° west of her former position, near the
Pleiades. But as she travels about 13° eastward
every day, she would be near the Pleiades on the
following evening, the 2nd of Nisan, so this year
was also counted normal.]
[Illustration: Fig. 9. Third Year, “full.” New Moon distant from the
Pleiades on the 1st of Nisan.
The sun is now 2 × 11 = 22 days’ march, or about
22°, short of his first position, and the young
moon consequently about 22° west of the Pleiades,
so she will not come up with them until the 3rd
Nisan, after travelling 2 × 13 = 26°. The year was
therefore “full,” that is an extra month of 29 days
was added, which is more than the 22 days needed to
enable the sun to reach his first position by the
1st of Nisan in the fourth year.
It appears, therefore, that the extra month must
have been added once in three or four years.]
Several lists of stars and star-groups indicating the months in this
way have been found, the early lists containing only a few, the later
twelve. If our zodiac originated with the Babylonians, there is little
doubt the idea took its rise from these monthly stars, but it is not
possible, with our present knowledge, to say when these old astronomers
first linked the isolated stars into a continuous series of twelve
star-groups and connected the idea of the month with the invisible
group among which the sun was known to be shining, instead of with the
stars seen east or west of him, or in conjunction with the crescent
moon.[21]
------------------------------------------------------------------------
[21] If Taurus was originally considered the first constellation of
the zodiac, instead of Aries, of which there are some indications, the
change may well be explained by this change of method. It does not
necessarily imply that the equinox was in Taurus when our zodiac was
invented. It was near ω Arietis in B.C. 1000.
------------------------------------------------------------------------
[Illustration: Fig. 10. The Scorpion.
From a boundary stone (now in the British Museum) set up in the reign
of Nebuchadnezzar I., king of Babylonia, about 1100 B.C.]
[Illustration: Fig. 11. The Goat, with Fishes’ Scales.
From a Babylonian boundary stone.]
A Scorpion with immense claws, and a Goat with fishes’ scales appear
several times on monuments at least as old as 1000 B.C. and it is very
probable, although this fact alone would not prove it, that they were
then used as constellation figures. It has been definitely proved from
inscriptions that before 600 B.C. the name of Scorpion was applied to
some stars of our present Scorpion, that there was a Lion corresponding
with ours, and the principal star in that asterism, which was called
“The King” by Greeks and Romans (Basiliskos and Regulus), bore a name
with the same meaning in Babylonia; the Celestial Bull seems to have
been the group of the Hyades, and the Great Twins were the two stars
Castor and Pollux. The last two identifications seem to show how the
single stars or small groups of the monthly lists were expanded into
the large zodiacal constellations, for the Hyades cluster is in our
present Bull, and Castor and Pollux are in our Twins.
Under the great Assyrian kings who in the 8th and 7th centuries
B.C. made Nineveh the capital of their empire, Babylonian astronomy
flourished exceedingly, and it made much progress through all the
political changes which followed, until the beginning of our era.
The motions, phases, and eclipses of the moon were carefully studied
and could be accurately predicted, the positions of many stars were
determined; the zodiac was divided into twelve equal spaces, which
afterwards became 36 by sub-division (the constellations being too
unequal in size for convenience); and finally the whole circle was
marked out in 360 degrees. The movements of all the naked eye planets
were well understood, their positions being constantly compared with
those of a number of standard stars, mostly in the zodiac; and after
watching and recording these for a number of years the astronomers
were able to calculate where each planet would be found at future
dates. Tables have been found on clay tablets of the 2nd century B.C.
predicting the heliacal risings and settings, and the stations and
retrogressions etc., with considerable accuracy.
When astronomy had reached this stage of accurate prediction, it was
no longer in its infancy, but was fairly on its way to become a true
science.[22]
------------------------------------------------------------------------
[22] A Babylonian treatise on astronomy recently published by the
trustees of the British Museum supports Kugler’s view that truly
scientific methods were not adopted before the sixth century B.C. This
treatise formed the subject of a lecture given by Mr L. W. King before
the Society of Biblical Archæology on Feb. 19, 1913.
------------------------------------------------------------------------
Nevertheless, the astronomy of the Babylonians, advanced as it was,
seems never to have progressed beyond the empirical stage. With them,
there seems to have been no desire to group the facts they so patiently
and skilfully collected into a system, and form a theory to explain
them.
And this must be said of other ancient nations also. The Egyptians made
careful observations, especially of the heliacal risings of different
stars, by means of which they determined the length of the year, as we
have already mentioned, and oriented their temples and pyramids. They
worshipped the sun in all his aspects, and their astrology so much
resembles the Babylonian that it is believed to have been derived from
it. The Babylonians seem to have been more interested in the planets
than any other nation of antiquity, but they were known also in other
countries. The Chinese recorded comets, and all races were greatly
interested in eclipses, which they were able to predict with some
accuracy, having discovered that they occur in cycles. Yet we find no
more rational attempt to explain these phenomena than the Hindu legend
of a great dragon that attacks the sun, or the Egyptian story of a sow
that swallows the moon; and their cosmogonies can only be regarded as
poetical descriptions or survivals of early childlike notions of the
universe.
The Hindu world resting on the back of an elephant, and that on a
tortoise, is no doubt but an allegory. The Egyptians pictured the
earth as a great parallelogram, long from north to south but narrow
from east to west, like their own land, with the sky over it, upheld
by huge pillars or lofty mountains. The stars were set in this domed
lid of the world, but sun, moon, and planets were floating each in its
own boat on a great celestial river which ran just below the summits
of the mountains, and whose course was hidden towards the north. The
bark of the sun came nearer to Egypt in the summer, because at that
time the celestial river overflowed its usual bank, like the Nile. The
red _Doshiri_ was said to sail backwards, referring no doubt to the
retrograde movement of Mars.
In Eridu, one of the oldest cities of southern Babylonia, on the
Persian Gulf, the great abyss of the ocean was looked upon as the
origin of all things, and it was believed that it encircled the
earth like a great river. Later on, we find the world described as a
great mountain, resting on the watery deep, and under the mountain
is the abode of the dead. It is entered from the west, which surely
was suggested by the setting of the heavenly bodies in the west. The
vaulted sky above the earth has divisions: the rim of the lowest part
rests upon the supporting watery deep; above it are the upper waters
(the source of rain); and above this again is the dwelling-place of the
celestials. The sun issues forth each morning from a door in the upper
heaven, or from the mount of sunrise, and enters another heavenly door,
or the sunset mountain, at night.
The similarity to these Babylonian ideas of the Hebrew “firmament,”
the “waters above the firmament,” and the “of the great deep,” in the
book of Genesis,[23] and Ezekiel’s “Sheol” in “the nether parts of the
earth,”[24] has often been noted.
------------------------------------------------------------------------
[23] Gen. i. 6, 7; vii. 11.
[24] Ezek. xxxii. 18, 24.
------------------------------------------------------------------------
[Illustration: The Boat of the Sun travelling over the sky. [_To face
p. 46._
From an ancient Egyptian papyrus.
The recumbent figure covered with leaves symbolizes
the earth; the figure leaning over Earth, covered
with stars, is the sky; the boat of the rising sun
and of the setting sun floats over it. The central
figure represents Maon, the Divine Intelligence
which preserves the order of the universe.
(_Reproduced from Flammarion’s ‘Astronomical Myths,’ by permission of
Messrs. Macmillan & Co._)]
To sum up:—
If we include as astronomy any observation of the heavenly bodies which
leads to a recognition of order and periodicity in their movements
and a power of forecasting their positions, then every race and age
has had its astronomers, rough though their methods may be at first.
With growing civilization more refined methods are used; the gnomon is
invented for studying the movements of the sun; the changing positions
of moon and planets are noted by means of certain stars; finally, all
the visible stars are grouped into constellations, and it is recognized
that a great band of star-groups crosses the sky, which forms the
pathway alike of sun, moon, and planets; the length of the month and of
the year are determined more or less accurately, and when an unvarying
calendar has been formed, the celestial cycles can be better recorded
and studied. But in all this there is as yet no scientific motive
properly so called, no curiosity regarding the phenomena for the simple
pleasure of knowing and understanding them, no attempt to group them
into a system or to explain their underlying causes. The primitive idea
that the heavenly bodies exist for the convenience of earth-dwellers
is illustrated by the Egyptian hieroglyph for night, [glyph] which
consists of the sign for sky [glyph] combined with a star suspended
like a lamp; the other idea that they are mysterious divinities is
shown by the Babylonian star-sign for a god or king, [glyph]. The
ancients found that the stars were of great use, especially for
measuring periods of time; they recognised also in them a marvellous
order and regularity, of which they dreamed that they found an echo on
earth, and endeavoured to divine the future by watching the skies. Can
we doubt that they were also attracted by the beauty that calls all men
through all ages to lift their eyes and look upward?
HYMN TO THE SETTING SUN.
_Sung by the Priests of Babylon._
Sun-god, in the midst of heaven,
At thy setting
May the latch of the glorious heavens
Speak thee peace.
May heaven’s door to thee be gracious,
May the Director, thy beloved messenger, direct thee.
Lord of E-bara, may the road of thy path be prosperous,
Sun-god, cause thy highway to prosper,
Going the everlasting road to thy rest.
Sun-god, thou art he who is judge of the land,
Causing her decisions to be prosperous.
From a lecture by T. G. PINCHES.
(_Nature_, Dec. 31, 1891).
_III. GREEK ASTRONOMY._
FIRST PERIOD. B.C. 900 TO B.C. 350.
“Great men! elevated above the common standard
of human nature by discovering the laws which
celestial occurrences obey, and by freeing
the wretched mind of man from the fears which
eclipses inspired! Hail to you and to your genius,
interpreters of heaven, worthy recipients of the
laws of the universe, authors of the principles
which connect gods and men!”
PLINY
(_Apostrophe to Thales and Hipparchus._)
1. HOMERIC GREECE.
To turn from the astronomy of Egypt and Assyria to the astronomy of
the Greeks is like coming to a sudden bend in a river which has flowed
through level country for many miles in a slow majestic course, and
finding beyond the bend a series of rapids and waterfalls. Instead of
patient age-long accumulation of observations, instead of a mystical
adoration of stars, supposed to be beyond man’s power to understand,
we find that the Greek’s first instinct is to inquire into the meaning
and the origin of what he saw, even before he had taken time to
investigate. Behind the varied splendours of earth and skies which
fascinated his bodily eyes, his intellect divined laws and forces which
held the whole together in a wonderful harmony. Then, as fresh facts,
or a fresh point of view, thrust itself upon him, a new explanation
must be attempted, and thus many complete systems of the universe were
evolved. Not the name only, the idea of Cosmos was Greek.
[Sidenote: Homer _c._ 900 B.C.]
[Sidenote: Hesiod _c._ 800 B.C.]
The first ideas of astronomy among the Greeks were as primitive as
those of any other race in its early stages. They evidently had no
conception of the sky as a sphere, or of the revolution of the stars
as a whole, round fixed poles, though they watched the motions of
certain bright star-groups, and called them by the names that we use
now (however these names may have reached them), as we see in Homer
and Hesiod. Ulysses, guiding his raft cunningly by night, keeps on his
left the Bear, also called the Wain, which turns round in her place and
keeps watch on Orion, and never bathes in ocean; he watches also the
Pleiades and the “slow-setting Ploughman” (Boötes)—an apt description,
as anyone may see who watches Arcturus, the brightest star of Boötes,
when low on the western horizon. Being a northern star, its motion
seems very slow, and makes so small an angle with the horizon that for
a long time Arcturus glides above it before finally dropping below;
whereas the Pleiades, or any other stars near the equator, move very
quickly and almost at right angles to the horizon, and so drop below it
quite suddenly. It is Ulysses also who warns his companion, when they
are setting out to spy upon the Trojan camp, that two watches of the
night are already past, “for the stars have gone forward.” The stars
also announced the seasons, for Hesiod says that the time of harvest is
indicated by the heliacal rising of the Pleiades, and when Orion with
Sirius stands in mid-heaven, and Arcturus rises in morning twilight, it
is time for the vintage.
Homer and Hesiod both mention Venus, as a morning star “the brightest
of all the stars, which comes to herald the light of dawn,” and also as
an evening star, apparently without recognizing that it was the same
star; as they do not mention any other planet we do not know if the
others were known to the ancient Greeks.
The first appearance of the new moon’s slender crescent was watched for
from hill-tops, and celebrated by sacrifices, and this—as with other
ancient nations—fixed the first day of their month.
[Sidenote: Mimnermus _c._ 580 B.C.]
Day seems to have been divided into three parts, morning, midday, and
evening, according as the sun was rising, or nearly stationary, or
sinking. The sun was thought to rest upon and slide over the solid dome
of the sky, otherwise perhaps it would have fallen to the ground; and
at night it was supposed to go behind Mount Atlas, and then to travel
behind high northern mountains to its rising place in the east. This
primitive explanation of its movements is so poetically described by
an early poet, Mimnermus, that I cannot resist a quotation, though the
lines can hardly be regarded as an astronomical fragment. They may be
freely rendered thus:—
Endlessly toiling Helios speeds.
No rest for him or for his steeds
When Dawn has climbed the height.
Soon as he lays his weary head
Upon the golden wingèd bed
Made by Hephaestos’ might,
It bears him sleeping o’er the seas,
Far from the fair Hesperides,
Through realms of darkest night;
Till in the Ethiopian land
He sees his horses ready stand;
And when the child of light,
The rosy-fingered, early-born,
Has ushered in another morn,
He mounts his chariot bright.
The earth, as pictured on the shield of Achilles, was flat and round,
just as it appears from a height, and of course Greece was the centre,
just as Egypt was the centre of the Egyptian, and Babylon the centre
of the Babylonian cosmogonies. It was a small earth: a few countries
lay round the Middle Sea, and further to the south was the land of the
Ethiopians where the Sun passes overhead and burns the inhabitants
black; there was another sea to the north, over which the Argonauts
sailed, and in the extreme east was the Lake of the Sun, out of which
he rose every morning. This was a great gulf of the River Oceanus which
encircled the whole earth. Its sources were in the furthest west, just
beyond the Pillars of Hercules, and thence it flowed north, east, and
south, finally returning into itself. A branch from near the source,
called the Styx, flowed down into the underground world of Hades, the
abode of the dead, and beneath this again was Tartarus, where were
imprisoned the Titans who had fought against Jove.
Above the flat earth the blue dome of heaven was spread like a tent,
and across it travelled
“The never-wearied Sun, the Moon exactly round,
And all those stars with which the ample brows of
heaven are crowned.”
What a compact little universe, and how important a part of it was man!
But as thought developed, the universe expanded.
2. THALES AND ANAXIMANDER.
[Sidenote: B.C. 585.]
[Sidenote: Thales _c._ 600 B.C.]
In the sixth year of the war of the Lydians against Cyaxares, king of
the Medes, just when a battle was about to begin, day was suddenly
changed into night by an eclipse of the sun, and Herodotus adds: Thales
had told the Ionians of this before, and in what year it would happen.
This does not necessarily imply any accurate understanding of eclipses
on the part of the Ionian philosopher. He had visited Egypt, and may
have learned from the priest-astronomers there that eclipses recur in
cycles and so can be predicted. But Thales was not content with cycles.
He wanted to know, not only that eclipses would happen at such and such
times, but _how_ they happened. Perhaps from reports of Babylonian
observations, perhaps from questions put to Egyptian astronomers, he
learned that solar eclipses only happen when the moon is new and in
the ecliptic, that is, in the same part of the sky as the sun, and
that the black body then seen on the sun has always a rounded edge.
These no doubt were the arguments on which he founded his assertion
that solar eclipses are caused by the moon passing in front of the sun;
and he further added that this shows the moon to be of an “earthy”
nature, that is, not made of fire or any substance either luminous
or transparent, but of opaque matter, probably having weight and
substance, and not altogether unlike what we know on earth. He is said
to have stated also that the moon receives her light from the sun,
a conclusion which would follow from a little attention and thought
bestowed on her phases.
Besides his speculations regarding the moon, Thales took pains to note
the sun’s movements as accurately as possible, by means of gnomons,
with a view to discover the exact length of the solar year, and it was
he who advised the Greeks to adopt the Phoenician method of directing
their course at sea by the Little Bear instead of the Great Bear, which
appears to have been the constellation used in Homeric times.
Thales imagined that Ocean did not merely encircle Earth, but that the
whole Earth, which was a thin flat disc, floated upon the Ocean.
This zealous observer must have had something of the absent-mindedness
of his great successor, Newton; for it is told of him that while
star-gazing he fell into a well!
[Sidenote: B.C. 611-545. Anaximander]
It is evident that the moon’s passing in front of the sun implies a
lesser distance from us, and it must have been this which suggested her
place in the scheme of Anaximander. This scheme is rather difficult to
understand, from the allusions and quotations of later writers, for
we have no original writing by Anaximander; but we can gather enough
to show that already in the sixth century B.C. the Greek philosophers
were asking themselves what was the explanation of the movements and
appearances of the heavenly bodies, how they were supported in the
sky, what force moved them, how large and how distant they were, and
what they were made of. Anaximander asserted boldly that sun and moon
were larger than the whole earth: he thought the sun might be 27 and
the moon 19 times as large. How he reached this conclusion it is
impossible to say. The Egyptians had already tried to measure the
apparent size of the sun as compared with the circumference of the sky,
by noting how long it took to set from the moment the lower rim touched
the horizon to the moment when the whole disc disappeared: this,
divided by the 24 hours taken by the sun to traverse the 360 degrees of
the sky, gave the sun’s size in degrees (it is about half a degree),
and had they been able to find the actual distance of the sun from the
earth, they could have deduced its actual size, but this they had no
means of determining.
There are two possible ways of seeing that the moon is smaller than
the sun, although they usually appear to us the same size. Anaximander
may have seen or heard of an “annular” eclipse, in which the moon is
rather more distant from us than at a total eclipse, and therefore
her dark body just fails to cover the whole sun, and a bright ring of
light surrounds her. More probably he realized what was implied in
Thales’ explanation of solar eclipses, and concluded that the moon must
be smaller than the sun, because she looks no larger although she is
nearer to us.
His scheme is the first of which we have any knowledge in which the
movements of the heavenly bodies are explained by supposing them not
all in one sky together, but placed in a series of heavens, one above
the other: hence it is of peculiar interest to the Dante student, for
in it we trace the first attempt towards the theory of the Revolving
Spheres. It is true that the Babylonians and Hebrews divided their
heaven into three parts, one above the other, but this was only to
divide the place of atmospheric phenomena from the dwelling-place of
the gods, and sun, moon, planets and stars all moved in the same
heaven. Here, in the universe of Anaximander, we find one heaven, the
lowest, for air, rain, etc., another for all the stars, a higher heaven
for the moon, a yet higher for the sun, and above all the region of
fire, the brightest, lightest element, whose nature it was to ascend
and which therefore is outside all, as it was the nature of earth
to descend and therefore to be at the bottom. Probably either in or
above the heaven of celestial fire was the heaven of the gods, for, as
Aristotle remarks, all our ancestors, indeed all who believe in gods at
all, whether Greek or of any other race, place the dwelling-place of
the gods above in high heaven, as the unchanging, unmoving region of
eternity.[25]
------------------------------------------------------------------------
[25] _De Cœlo_ I. 3, and II. 1.
------------------------------------------------------------------------
Unfortunately we do not know what would be of great interest, whether
Anaximander also provided separate heavens for the planets, or found
a home for them in the heaven of the stars. Perhaps he hardly knew of
their existence, or said with Aratus who wrote nearly 800 years later:—
“Of these I dare not speak with certainty,
As of the fixed stars’ orbits.”
The successive heavens were in layers, as it were, one above the
other, “like the bark enclosing a tree,” but they were transparent and
invisible. The heavens themselves were not in motion, carrying the
stars, sun, and moon; Anaximander had an ingenious mechanical scheme
of wheels or rings to carry them inside their respective heavens,
which doubtless was clear to himself, though unfortunately it is not
at all clear to us. Some writers have maintained that these heavens
were spheres, but for several reasons it is difficult to believe this,
and probably the sky was still to Anaximander, as to the Homeric
Greeks, a slightly flattened hemisphere,[26] only divided into these
layers, and instead of ending at the horizon it continued a little
below, to allow of the passage of the heavenly bodies between setting
and rising. Perhaps it was for this reason that he gave the earth a
greater thickness than the disc of Thales, comparing it to a short
thick pillar, three times as broad as high, the top of which only was
inhabited. His Cosmos, then, would be something like the diagram, with
regard to the disposition (though not the relative sizes) of Earth and
the heavenly bodies.
------------------------------------------------------------------------
[26] But see note, pp. 75, 76.
------------------------------------------------------------------------
[Illustration: Fig. 12. The Universe according to Anaximander.]
Somewhat timidly the barriers have been thrust back. The earth goes a
little deeper into the dark unknown, the sky is wider and higher, the
heavenly bodies are much larger and more distant and go under Earth’s
surface; but they are cautiously upheld by solid domes, and worked by
wheels. Earth is still the floor of the World, and Heaven—now a series
of heavens—the vaulted roof above.
3. LATER FLAT EARTH SYSTEMS.
It is interesting to see how long this timidity persisted among the
Greek philosophers, especially of the Ionian school, in spite of the
fact that other schools had advanced much bolder ideas, as we shall
presently see. Quite a number of universes were constructed somewhat
after the pattern of Anaximander’s, with Earth as floor of the world;
but some placed the stars beyond moon and sun, some definitely included
the planets, though they do not seem to have explained their motions;
and there were various ways of supporting the flat earth, and of
supporting and moving the heavenly bodies.
[Sidenote: Anaximenes _c._ 550 B.C.]
[Sidenote: Empedocles _c._ 450 B.C.]
[Sidenote: Anaxagoras died 428 B.C.]
Anaximenes, a follower of Anaximander, having doubtless pondered
the fact that very heavy bodies can float in water if only they are
the right shape, and that Earth itself was supposed by Thales to be
floating on the Ocean, suggested that the moon is so broad a disc that
she floats in the ether, “like a leaf,” and of course the same would
apply to the sun. Two later philosophers, Empedocles and Anaxagoras,
held that a great whirlwind swept continually round the Earth, which
both kept the heavenly bodies from falling down upon it and drove them
across the sky.
Equally diverse were the opinions as to the nature and composition of
the heavenly bodies. Most philosophers of this age believed that they
were of pure fire, or else that they were vessels containing fire,
which was extinguished, or in one way or another became invisible to
us, during eclipses and when they set. Others held, as we have seen
with Thales, that they were of an earthy nature; and Anaxagoras, seeing
a meteorite which had fallen from the sky during the daytime, thought
he actually held a piece of the sun in his hands, and concluded that
the sun was an enormous mass of iron, “much greater than Peloponnesus,”
and shone because it was red-hot. But the popular idea still was that
the sun was a god, or the chariot driven by a god across the sky, and
Anaxagoras was banished from Athens for his impious words.[27] The
markings on the face of the moon were thought to prove that she was of
mixed composition: she was made of air mingled with only a little fire,
or earth mingled with fire; but according to Democritus the markings
were shadows of mountains on her surface, and Anaxagoras is reported to
have said that the moon was inhabited, and the markings were “plains
and valleys.”
------------------------------------------------------------------------
[27] His life was saved by his illustrious pupil, Pericles, of whom
the story is told that on one occasion, just as his army was embarking
for an expedition, the sun was eclipsed, and his pilot was terrified.
Pericles snatched off his cloak, and held it so as to hide himself from
the man’s eyes. “Is that terrible? is that an evil omen?” he cried.
“Then do not fear the disappearance of the sun, for it is just the
same, only the thing that hides it is larger than my cloak.”
------------------------------------------------------------------------
Anaxagoras suggested that the stars were fragments torn off the
circumference of the earth by the encircling whirlwind, and that they
glowed with the heat caused by friction, though they were too distant
for us to feel this heat, being far beyond the sun. The Milky Way was
a source of speculation: some said it was the former path of the sun,
and still burning from his heat, but Democritus explained it as caused
by the shining of innumerable stars, too faint and close together to be
distinguished separately.
The doctrines of the different philosophers as to origin and first
stages of the universe do not concern us here, but we must mention that
of Empedocles, as his views are directly referred to by Dante.
This philosopher was the first to assert that everything consists of
the four elements, earth, air, water, and fire, pure or in combination;
and the combinations he supposed to be brought about by two forces, one
attractive, the other repulsive, which he named Love and Discord. Of
these, one alternately predominates at different ages of the world, and
thus its history is divided into periods of different character.
A great step forward was taken when it was realized that the sky is not
a hemisphere, ending at the horizon, or even extending a little way
below, but that it surrounds Earth in every direction, like a sphere.
This idea probably originated with the Pythagoreans, or it may have
occurred independently to several thinkers, when the diurnal motion of
the heavens was better observed, and geometrical conceptions understood
and applied. Now it became no longer necessary to extinguish and
rekindle the stars, nor to send the sun round swimming on River Ocean
behind northern mountains, or creeping through strange underground
regions, through the night. It was clearly recognized that the visible
course of each heavenly body was part of a circle, the whole of
which we could see if we could only travel fast enough and go to the
underside of the earth.
[Illustration: Fig. 13. The Universe of Leucippus.]
[Sidenote: Leucippus _c._ 450 B.C.]
[Sidenote: Democritus _c._ 430 B.C.]
But this was just what never could be done, for outside the schools
of the Greeks in Italy (Pythagorean and Eleatic), Earth still had
an uninhabitable underside. Distinguished men like Leucippus and
Democritus sought to combine the belief in an all-surrounding spherical
heaven with a flat supported earth which might still give them a solid
floor beneath their feet. Leucippus made the earth a hemisphere, with a
hemisphere of air above, the whole surrounded by the supporting crystal
sphere which held the moon. Above this came the planets, then the sun,
and probably the stars were outside this. His disciple, Democritus, on
the other hand, retained the disc-like earth, raised a little at the
rim, to secure its contents, and made it divide the sphere of air into
two parts, so that it rested upon air, and air was also in the sky
above. The underside of the disc was not inhabited, no doubt because
no one could stand upside down. His order of the successive heavens is
not quite the same as that of Leucippus, as he puts the moon and the
Morning Star together, and the rest of the planets beyond the sun.
[Illustration: Fig. 14. The Universe of Democritus.]
This scheme gave the universe a beautifully symmetrical form, which
must have pleased the Greeks, but now they were puzzled to know why
the heavenly bodies did not circle symmetrically with regard to the
central earth. Why was not the pole in their zenith and the equator on
the horizon? They could only guess that it must have been so at first,
and that the disc had slipped out of position, either through some
irregularity in its weight, or in the density of the underlying air.
Compare Milton’s—
“Some say He bid His angels turn askance
The poles of Earth twice ten degrees and more,
From the Sun’s axle; they with labour pushed
Oblique the centric globe.”
_Paradise Lost_, Bk. X., 563-566.
All these theories and guesses may seem to us very crude and fanciful,
and we may compare them to the eager questionings of intelligent
children, too impatient to consider whether the answers given are
satisfactory explanations or no. But we must remember that all we know
of the early cosmogonies is from allusions and descriptions by later
writers, who often—like Aristotle, for instance—only quote to condemn.
“If each could defend his own opinion, may be we should see that there
is truth in all.” (Conv. IV. xxi. 25-7).
At least we find a keen and disinterested desire to penetrate the
causes of things, and a fertile imagination, without which science
can make no advance: moreover there was a progress in true knowledge.
It was discovered that the (apparent) diurnal paths of sun, moon, and
every star were circles, although only a part of the paths could be
seen; and that, although all were seen projected on a sphere, their
actual distances from earth were very varied.
It is disappointing to find no record of observations of the planets,
and from the almost random way in which they were placed in the heavens
it seems that but little attention had been paid to them as yet. In
fact, Seneca tells us that Democritus knew neither their number nor
their names. They were often classed with comets, and thought to be
entirely erratic, and the Greek mind was more attracted towards those
phenomena which were seen to be orderly.
4. PYTHAGORAS AND HIS FOLLOWERS.
_Socrates._ As the eyes are appointed to look up
at the stars, so are the ears to hear harmonious
motions, and these are sister sciences. That is
what the Pythagoreans say, and we, Glaucon, assent
to them?
Yes, he replied.
[Sidenote: Pythagoras _c._ 540 B.C.]
About the same time that Anaximander was inventing solid hemispheres
and rings to hold and move the heavenly bodies round about a flat
earth, Pythagoras was founding a school in southern Italy which gave
to the world a very different scheme. One of the characteristics of
his school was secrecy, its methods were oral, and his later followers
were fond of attributing to their master everything which had gradually
grown out of his teaching: it is difficult therefore to say with
certainty what he himself taught. It has often been stated by modern
writers that he anticipated Copernicus, and discovered that the earth
revolves round the sun. Though this is a mistake, we may venture to
believe that Pythagoras taught that the earth is a sphere, hanging
freely in space.
We are so familiar with this idea from childhood, that it is difficult
to imagine what a tremendous innovation it was. Pythagorean noviciates,
doubtless after solemn initiation and preparation, were told: This
earth, which seems to you the floor of the world, with heaven stretched
over it like a tent, is a round globe, with men like you living on
the other side of it, and yet they do not fall, and earth does not
fall, for it is poised in the centre of the world, and has no tendency
to fall in one direction rather than in another. Earth, itself a
perfect sphere, is in the centre of an infinitely greater sphere, the
star-set heaven; and within this seven heavenly bodies move in perfect
circles, each at its proper distance and pace, all needing no support
and no force to drive them, for harmony is the motive power of the
Cosmos. Their distances are proportional to the intervals between
musical notes, and as they circle they make heavenly music, which we
should hear did we not always hear it, like one who lives beside a
waterfall[28]. There is no below, and no above, for above is below and
below above to our antipodes: there is but the centre, where we live,
and Heaven is all around.
------------------------------------------------------------------------
[28] Some late followers said that Pythagoras, alone amongst men, could
hear the music of the spheres.
------------------------------------------------------------------------
How did Pythagoras reach this great and startling truth of the round
unsupported earth?
His school relied more on experiment and observation than the Ionian,
and the colonizing Greeks of Italy had travelled. They might have
noticed the curvature of the sea, and the varying height of the Pole
Star according to latitude. We know that in early days the Greeks were
struck by the remarkable fact that the brilliant star Canopus (second
only to Sirius in brightness), which was invisible in Greece, could
just be seen close to the southern horizon in Rhodes, and was well
seen in Egypt. Then the moon may have helped once more. When it was
understood that lunar eclipses only happen at full moon, when we are
between her and the sun, and that they may therefore be explained by
the earth’s shadow falling on the moon, then, since the edge of that
shadow is always a circle, it is demonstrable that the body throwing
that shadow can have no form but that of a ball.
Sun and moon are obviously round: it was guessed that they also are
globes rather than discs, and the spherical shape of all heavenly
bodies was a doctrine of the later if not the earliest Pythagoreans.
Whatever may have been the steps which led to these two great
discoveries that Earth is a sphere, and that the apparent path of
every celestial body is a circle, the sphere and the circle were soon
accepted as the only forms suitable for celestial bodies and their
orbits. The founder of the school was a great mathematician, and it
is not strange that these forms should have commended themselves to
his disciples. The sphere, which has its surface everywhere similar,
and its contents greater than those of any other figure with equal
surface, was the “most perfect” of solids; and the circle, which has
no beginning and no end, is alike in every part, and presents ideas
of haunting suggestiveness to the geometer, was the “most perfect” of
lines.
In the system of Pythagoras we first find the five planets distinctly
enumerated, and playing as important parts as sun and moon. Number was
the principle of this universe, and the planets with sun and moon made
the sacred number of seven. Among the Greeks, and through the middle
ages, all these bodies are spoken of as planets or “wanderers,” in
distinction from the “fixed” stars which do not appear to move amongst
themselves. These seven “planets” represented the seven notes of a
musical scale, and the star sphere made up the octave. Pythagoras is
said to have been the first to teach that Phosphor and Hesperus, the
morning and the evening star, were the same. When, however, we ask
what was the order of the planets in his scheme, we meet with many
conflicting reports, and a serious difficulty suggests itself. If
the planets had really been observed with care, it must have been
seen that their motions could not be accounted for by simple circular
movement. The large oscillations of Mercury and Venus on either side
of the sun would strike an observer before he thought of tracing their
movements among the stars, and noting that they made a circuit of the
zodiac. Similarly, the other planets are most conspicuous, rising after
sunset and remaining long visible through the night, at the very time
of their retrograde movements, so these must have been noticed if a
long enough series of observations had been made to distinguish them
from one another. The only solution of the difficulty seems to be that
Pythagoras, on the journeys into Egypt and Babylon which he is said
to have made, learned that there exist planets to the number of five,
which move in regular periods, and he may also have learned the length
of their zodiacal periods at the same time, or perhaps these were only
known to his school much later. If the order assigned to them was that
which was finally and generally accepted by the ancient world, the
periods must have been known, for this is the only possible clue to the
order Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn. The planet with
shortest period (the moon, with a month) was naturally placed by the
Greeks nearest to earth, with the smallest circle to traverse, and so
on outwards.
It is very possible, however, that the early Pythagoreans, at least,
did not venture to assert more than that there were five planets,
without assigning to them any order, for Aristotle tells us that their
universe was divided thus:—
From Earth to Moon was the Ouranos, or sky, within which exists all
that is changing and corruptible.
Cosmos, the place of ordered movement, was the region of Sun, Moon, and
Planets.
Olympos, the place of pure elements, held the stars; the region of
Celestial Fire came beyond this, and the Apeiron, the Infinite Space,
or Infinite Air, from which the world draws its breath, was outside all.
[Sidenote: Philolaus towards end of 5th century B.C.]
The diagram shows, then, the earliest form of the Pythagorean universe.
But they did not remain content with this. Out of it grew a most
interesting scheme (referred to by Dante), which is usually attributed
to one Philolaus, of whom hardly anything is known, not even his date.
It seems to have struck Philolaus as a difficulty that the seven
planets, which were circling round Earth in the same direction but
at very different distances and speeds, and also the immense sphere
of stars beyond, were all sweeping together at the same time in an
opposite direction, and at the almost incredible pace of one revolution
in a day. The brilliant idea occurred to him: Leave the stars at rest,
let the seven planets revolve in their seven orbits, the nearer to the
centre the faster, and let earth herself revolve fastest of all, viz.
in twenty-four hours, in the same direction. If she keeps one face
always turned towards the centre, like the moon, this will account
quite as well for the apparent diurnal revolution of all the heavenly
bodies, and the change of day and night on the earth.
Philolaus did not make Earth remain stationary and simply turn on her
axis, which would have had just the same effect on the apparent motions
of the heavens; for it seemed more natural that she should revolve as
did the rest. The five naked eye planets are all mentioned by name in
his scheme.
[Illustration: Fig. 15. The Universe of Pythagoras.]
Was the centre, deprived of Earth, to be left empty? No, the centre
was the Watch Tower of Zeus, the Hearth of the Universe, and here they
placed the purest element, fire. It was invisible to us, because we
live on the side of the earth-sphere turned away from the centre; and
also invisible to us was another planet, Antichthon, or Counter-Earth,
for this revolved within our orbit, and also in twenty-four hours. It
was added to the system, because the addition of Earth as a heavenly
body spoiled the sacred number of seven, but by adding Antichthon, and
counting the star sphere as another, the total was brought up to ten,
another sacred number.
The objection was made that, if Earth is moving in space, this must
bring about a change in the apparent sizes of sun and moon, as Earth is
nearer or farther from them, but the Pythagoreans were quite ready to
believe that all the heavenly bodies are so distant that this journey
of Earth makes no difference to their apparent size or brightness. The
planets were thought to be worlds like ours, and inhabited; and it was
even guessed that plants and animals on the moon must be fifteen times
as strong as ours, apparently because there the average day consists of
nearly fifteen of our days (of twenty-four hours), and the nights are
equally long.
It was the braver of the Pythagoreans to shake the steady earth from
her centre, and set her whirling in the depths of space, that they
realized, as no one had done before, how large she must be; for Greece
and the surrounding lands, the Middle and the other seas, instead of
making the whole of the earth, were now understood to be only a portion
of a great globe.
[Illustration: Fig. 16. The System of Philolaus: night on earth.
Only the side turned away from the centre is inhabited: consequently
the Central Fire and Antichthon are invisible.]
[Illustration: Fig. 17. Twelve hours later: day on earth.
Earth has made half a revolution and her outer side is now lighted by
the sun, which has only moved about half a degree forward in its yearly
orbit. Antichthon has also made half a revolution, therefore remains
invisible.]
Here, then, is a conception of the Universe widely different from
Homer’s. The little flat disc has become a great round ball, a planet
among planets, swiftly moving through space; the crystal dome that
tenderly covered it like a bell-glass over some fragile flower, has
lifted, and the vast sphere is seen, infinitely distant, and studded
with enormous stars. Man himself is now a tiny creature on a great
earth, and his world but one among many, but if he is humiliated by his
insignificance, is he not elevated by the vastness of his outlook?
[Illustration: Fig. 18. Earth and sun according to Heracleides.
In the upper figure it is day, in the lower, night, on the inhabited
side of Earth. The sun is on the equator, as at the time of equinox.]
[Sidenote: Heracleides _c._ 370 B.C.]
But not even here did the Greeks stop. It was taking a less startling
step than they had already taken, to reach the truth that Earth was
merely rotating on her axis once in a day, and so causing the apparent
diurnal revolution of the heavens. This step was taken (it is said)
by a Pythagorean called Hicetas of Syracuse, who is quoted as saying
that the earth, “while it turns and twists itself with the greatest
velocity round its axis, produces all the same phenomena as if the
heavens were moved and the earth were standing still.” We are told also
that “Heracleides of Pontus and Ecphantus the Pythagorean let the earth
move, not progressively, but in a turning manner like a wheel fitted
with an axis, from west to east round its own centre.”