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CORNELL
UNIVERSITY
LIBRARY
THIS BOOK IS ONE OF
A COLLECTION MADE BY
BENNO LOEWY
1854-1919
AND BEQUEATHED TO
CORNELL UNIVERSITY
E&ysical Sciences libraryCHART of SPECTRA
Hanhart lith.ASTRONOMY.
BY
J. RAMBOSSON,
LAUREATE OP THE INSTITUTE OF FRANCE (ACADEMIC FRAN^AISE AND
WITH NUMEROUS ILLUSTRATIONS.
JLontton:
CHATTO AND WINDUS, PICCADILLY.
1878.LONDON :
BRADBURY, AGNEW, <fc CO., PRINTERS, WHITEFKIARS.PEEFACE.
The late Father Gratry, Member of the French
Academy, once said : “ It is astonishing how ignorant
the great bulk of the public are in regard to astro-
nomy. I have known men of education maintain that
the ancient system of astronomy (which they con-
sidered to be the most philosophical, and branded me
as an empiric for not agreeing with them) was the
true one; that the sun revolved round the earth, not
the earth round the sun.
“ Thus is it that this science, so simple, easy, re-
gular, luminous, majestic and religious, so full, in all
its details of the deepest interest, a model of all other
sciences and a masterpiece of human intelligence has
not only failed to become popular, but is even un-
known to the great majority of those who have re-
ceived a liberal education. It is true that the fault
mainly lies in the defective manner of its teaching.” *
These remarks are, unfortunately, borne out by ex-
perience, and therefore justify me in adding another
* See Father Gratry’s Sources, Part i., p. 136.IV
PREFACE.
to the list of publications, many of them very excellent
ones, which have been put forth with the view of
popularising this science. It, of all others, inspires
the most grandiose ideas, calculated at once to elevate
the mind and develop the intelligence; it is also, as I
believe, one of the branches of human knowledge, the
principles of which can be the most easily compre-
hended when they are expounded in clear and simple
language, divested, that is to say, of technical terms.
This volume has long been in preparation. So
early as 1852 I pointed out in an influential news-
paper the progress of science, and in the columns of
La Science pour tons, of which I was editor-in-chief
for several years, the successive discoveries of the
astronomers were carefully registered. In 1865 I
published an elementary treatise, which had an ex-
ceptionally large circulation, and since then, a more
complete work, which was adopted by the official
committee of the Ministry of Public Instruction.*
* It was in reference to this publication that M. Babinet, of the Institute,
wrote me the following lines :—
“ My dear Rambossox :
“ I have read your work on Astronomy with much interest, and have
satisfied myself that the clearness of the language lias not prevented it from
being scientifically exact. I have in particular noticed that you have set
forth the most recent advances in Astronomy, so as to bring them within the
reach of ordinary intelligence, &c.
‘1 Ever yours,
“ Paris, March 8, 1866.	'	“ Babixet, of the Institute.”PREFACE.
V
My final task is therefore facilitated, as my func-
tions and inclination have led me to note each new
fact as it appears, and these will be found chronicled
in the following pages. I have also made a conscien-
tious compendium of the most advanced and best
authenticated theories, to which I have adjoined my
own personal observations.
My labour, too, has been materially lightened by
the house, or rather dynasty, which has undertaken
the publication of this work; and I have also to thank
the artists who have supplied me with the illustrations,
which will be found of unusual excellence. It only
remains for me to express a hope that the public to
whom I address myself will find this book worthy of
their notice.CONTENTS,
CHAPTER I.
ORIGIN AND PROGRESS OF ASTRONOMY.
Origin of Astronomy—Antediluvian traditions—Astronomy amongst
tlie Indians—Astronomy amongst the Chinese—The Emperor
Chun’s Sphere—The Astronomers Hi and Ho put to Death for
having neglected their duty—A remarkable Antique Text—Astro-
nomy amongst the Chaldseans—Abraham as an Astronomer—The
Book of Job—Astronomy 2000 years before our Era—Ancient
collection of Observations taken at Babylon—The Egyptians and
Astrology—The circular Zodiac of Denderah—The great Pyramid
of Gizeh, from an Astronomical point of view—The Ptolemies,
Kings of Egypt, Patrons of Sciences and Letters—Thales, Anaxi-
mander, Anaxagoras, Pythagoras, Pytheas, Aristarchus, Aristotle,
Hipparchus, and his Catalogue of 1022 Stars—Julius Caesar,
Sosigenes the Astronomer, and the learned Achorseus—Pompev and
the gifted observer of silent Olympus—Ptolemy and his School—
The Arabs and Almagestes—Copernicus, his System, his Appre-
hensions, and his Swan-like Song before Death—Galileo’s exclama-
tion : “Oh! Nicholas Copernicus ! ” — Tycho-Brahe and his
System — Uranienburg — Descartes, Philosopher and Savant—
Newton and his splendid Discoveries •••«..
CHAPTER IL
THE SOLAR SYSTEM.
The Sun—The eight principal planets—The smaller planets—The
satellites—Formation of the solar system .....
pack
1
33Vlll
CONTENTS,
CHAPTER III.
LIGHT AND THE DETAILS OF SPECTRUM ANALYSIS.
PAG®
Light enables us to recognise the stars—Revelations by spectrum
analysis—Hypothesis of the emission, and that of undulations—
Laws of light—Various measurements of its speed—The solar
spectrum—Chemical action of light—Length of luminous waves—
Analogy between sound and light—Molecular vibrations and
atomic vibrations—Mode of propagating light—Refraction and
reflection—Luminous interferences—How light added to light
produces darkness—Triumphal entry of the spectrum analysis into
science—Its history—Metals revealed by analysis of the spectrum
which they elicit during combustion—Important chemical and
spectral laws—Curious experiments in physiology—Undreamed of
horizons in astronomy — Ignition in the celestial domain—
Spectra of planets, moons, and stars—Substances discovered in the
stars—Nature of nebulaj—Movements of the stars revealed by
their spectra—Discovery of the nature of comets—Matter fol-
lowing in the track of the aerolites—Unity of composition
extending to all the luminaries in the universe—The inhabited
celestial spaces..................................40
CHAPTER IY.
THE SUN.
Its nature—Light and Aspect presented by its Surface—Grains of Rice,
“Willow-leaves, Straw-motes, &c.—Pores, Faculas, and Spots in the
Sun—Formation, nature, and motion of Spots—Rose-coloured
Shadows, Red Protuberances—Change of Shape in the Spots—The
Sun obfuscated by their enormous quantity—Rotation of the Sun
—Synodical Revolution—Sidereal Revolution—Periodicity of the
Spots—Solar Electricity and Hydrogen upon the Earth, and in
the Planetary Regions—Solar Explosions—Constitution of the
Sun—Two opposite hypotheses—Is'the Sun inhabited?—Curious
Anecdote—Recently acquired notions about the Sun—Tempera-
ture of the Sun—Curious Calculations—Is there any probability
of the Sun ever ceasing to shed light, heat, and life upon the
Earth—Lucretius and our modern Astronomers—Zodiacal Light:
its nature—Some parts of the Sun more brilliant than others—
Atmosphere of the Sun—Various elements of which the Sun is
composed—The Seasons—Dimensions and distance of the Sun—
Variation of its Diameter — Its influence upon the Earth —
Recapitulation .......	.	.	66CONTENTS,
IX
CHAPTER V.
MERCURY.
Its phases—Truncation of its crescent—Prodigious height of its moun-
tains— Mercury’s passage across the Sun—Its volcanoes — Its
distance from the Sun—Its seasons—Its density, mass, dimensions,
and motions—Strange peculiarities of this planet—Is it inhabited ?
—Fontenelle’s opinion...........................
CHAPTER VI.
VENUS.
Different names of this planet—Its distance from the Sun—Its trans-
latory motion—Why does it seem to vary in size ?—Pull and pale
light occasionally emitted by its obscure part—Visible in full day-
light—Curious facts : iEneas in his voyage to Italy, and General
Bonaparte at the Luxemburg—Discovery of the phases of Venus—
Curious anagram—Spots observed in Venus—Its gigantic moun-
tains—Explanation of its phases—Its passage across the Sun’s disc
—Its atmosphere—Why does it seem to remain longer to the east
and west of the Sun than it takes time to revolve around it ?—
Means of ascertaining the Earth’s distance from the Sun by the
passage of Venus—Halley, Le Gentil, Chappe—Curious facts—
Its rotatory motion around an axis — Its days and seasons—
Description of this planet and its possible inhabitants .
CHAPTER VII.
THE EARTH.
Its origin—Its transformations—Summary of what is known concerning
the globe’s crust, by Elie de Beaumont—Cooling of the globe—
Temperature of the Celestial regions—Shape and dimensions of
the Earth—Its chief divisions : continents and seas—Proofs that
the Earth is almost spherical—Flattened shape at the Poles—
Attraction—Its various kinds—Exact date of the establishment of
the law of attraction—Scientific hypothesis as to this law—History
of M. Bertrand’s measurement of the Earth—Various motions of
the Earth—Kepler, his genius and discoveries—The seasons—
Variations of day and night—History of the Earth’s translatory
motion round the Sun, by Arago.	.................
PAGE
113
118
129X
CONTENTS.
CHAPTER VIII.
THE MOON.
PAGE
Nature of the Moon—Its size—The light which we receive from it
when it is at its brightest—Heat reflected from the Moon ; history
of the discovery—Shadow’s, spots, craters, mountains, and extinct
volcanoes, observed upon the Moon’s disc—Its various motions—
Sidereal revolution—Surprising velocity of the Moon’s motion—
Is it possible for the Moon to fall on to the Earth—Successive
applications of the principle of gravity in explanation of the solar
system—Problem of the three bodies—Simple and easy experi-
ments in explanation of the Moon’s phases—Ashy light— Symboli-
sation of the Moon; curious passage from Sophocles .	.	.185
CHAPTER IX.
THE ECLIPSES.
Principal eclipses—Occultation—Theory of the eclipses of the Sun and
the Moon—Partial, total, or central eclipse—Appulse—Luminous
corona, protuberances, prominences, rose-coloured flames noticed
during eclipses—The most remarkable solar eclipses—Measure of
the eclipses—Immersion and emersion—History of the informa-
tion about eclipses from what has been remarked during their
occurrence—Terror which eclipses formerly inspired — Curious
facts—Meton’s cycle—The golden number—Saros—Instruments
for indicating past and future eclipses—The utility of eclipses in
fixing doubtful dates—Historical facts—Christopher Columbus
and the islanders—Pericles and his pilot — Pelopidas and an
eclipse of the Sun—The soldiers of Panins Emilius and an eclipse
of the Moon—Terror of Nicias, the Athenian general—Remarkable
passage from Plutarch...............................204
chapter x.
THE TIDES.
Their nature—The first of the Greeks wdio inquired into the causes
of this phenomenon—Passage from Lucanus—Influence of the
Moon and the Sun upon the v*aters—Theory of tides—M. 'De-
launay on the tides—Solar and lunar tides—Obstacles to tides—
Height of tides in the Moon—Flood-bar or “ bore ”—M. Babinet’s
description—Utility of tides—A charming allegory .	.	.
228CONTENTS.
N1
CHAPTER XI.
THE PLANET MARS.
PAGE
Recent observations of tlie planet Mars—Its close analogies with the
Earth—Its reddish aspect—Its atmosphere—Its soil—Its different
names—Curious mistakes to which the distances of Mars from
the Earth may give rise—The seasons in Mars—Its poles of ice
* and snow—Its forests, seas, and islands—Dimensions, translation,
rotation, and phases of Mars .......	238
CHAPTER XII.
JUPITER, SATURN, URANUS, NEPTUNE.
Jupiter—Its distance from the Sun—Its motions—Aspect of its surface
—Its dimensions—Its satellites—Their eclipses and the velocity of
light—Saturn—Its distance from the Earth and from the Sun—
Saturn’s ring—Nature of this ring—Its aspect—Its dimensions—
Various hypotheses—Uranus—Its motions—Its dimensions—Its
satellites—Neptune—Its distance from the Sun — Its rotatory
motion round the Sun—Its perturbations.............246
CHAPTER XIH.
THE STARS.
Fixed stars—Wandering stars—Number of stars—The stars seen
through the telescope —Illusion caused by the aspect of the celes-
tial vault—Distance of the stars from the Earth—Bewildering
calculation—The stars nearest to the Earth—Stars of different
sizes—The method of classifying and calculating them—Number
of stars of each order—The Milky Way—Its nature and shape
—From one surprise to another—The rank occupied by our Sun
in the creation—Incalculable number of suns—Ideas formerly
entertained concerning fixed stars—General motion of the whole
solar system in space—The laws of attraction in the most remote
regions of the sky—Planetary system of the stars—Double and
treble stars—Splendid revelation of spectrum analysis—Elements
of which the stars are composed—Types to which they appertain
—Ideas concerning immensity, and the stellar bodies which it
contains—Division of the stars into constellations—The constel-
lations in ancient times—Historical and legendary ideas—Northern
constellations situated above the zodiac—Constellations of the
zodiac—Constellations situated below the zodiac ....	258Xll
CONTENTS.
CHAPTER XIV.
THE COMETS.
PAGB
Description of a comet; its different parts—The nature of comets
—The opinions of modern and ancient astronomers—Terror which
comets formerly inspired — Recent comets — Periodic comets—
Changes to which comets are liable, both in regard to their
shape, motion, and course—Their volume and mass—Possibility
of a comet coming into contact with the Earth—Result of the
shock—Density of the various portions of a comet—The passage
of the Earth through the tail of a comet—Account of the chief
periodical comets—The comets of Halley, Encke, Biela or Gam-
hard, Faye, Brorsen, d’Arrest, Tuttle, and Winnecke .	.	.	289
CHAPTER XV.
SHOOTING-STARS, BOLIDES, METEORITES, ETC.
These phenomena alluded to by Homer, Ossian, Milton—Phenomena
which must not be confounded with each other—Meteorites and
their sub-divisions—Gaseous or pulverulent matters reaching the
terrestrial atmosphere from the planetary regions—Showers of
Sahara sand observed at a great distance from the desert—Appari-
tions, motion, number, shape, composition, and weight of
meteorites—History of principal meteorites—Meteorites of the
rivers iEgos-Po tamos and Abydos—Cybele and the Sun wor-
shipped in the form of meteorites—Extraordinary bolides, as
related by Plutarch—Meteorites in the Paris Exhibition of 1867—
Modern savants and the meteorites ; the pertinacity of M. Chladni
—Shower of aerolites in 1803, which were observed by M. Biot—
Hypotheses suggested in explanation of these phenomena—Are
meteorites found in the atmosphere ?—Are they asteroids or small
planets ?—The Moon, a troublesome neighbour—Analogy between
meteorites and comets—Has the Biela comet been transformed
into meteorites?—Periodical apparitions—Radiant points—Periodic
and sporadic shooting-stars—Days and months when shooting-
stars are most numerous—The influence of the precession upon
their apparition—Shooting-stars and the Chinese — Meteoric
currents — Shooting-stars subject to the general laws of the
universe...........................................317CONTENTS.
Xlii
CHAPTER XVI.
THE DIVISION OF TIME.
PAGE
Division of time; the day, week, and month—The year; that of the
Egyptians and of the Chaldaeans—The Olympiads—The Roman
year—Months added by Numa—Curious passage from Plutarch;
different lengths of the years—The Julian year—The Gregorian
calendar—Reckonings of the Sun and Moon amongst the Mexicans
—Russian and Greek dates—The solar cycle—The lunar cycle or
golden number—Period called Saros by the ancients—The epacts
—Composition of the calendar—The calendar and meridian—The
absolute time and the mean time—Precession of the equinoxes—
Great year, or the world’s year............... .	343
CHAPTER XVII.
ASTROLOGY.
Dogmas of the astrologers—Curious facts—Natural astrology—Judicial
astrology—Hippocrates—Virgil—Horace — Juvenal — Plutarch—
Tacitus—Tiberius and Thrasyllus—Astrology in Mexico—Monte-
zuma and the astrologers—Marsilius Ficinius—Pensa—Doctrines
of the astrologers—Albert the Great—Thurneisen—Catherine de
Medicis—Sensible advice given by Horace •	•	•	•	357ASTRONOMY
CHAPTEB L
ORIGIN AND PROGRESS OF ASTRONOMY.
Origin of Astronomy — Antediluvian traditions—Astronomy amongst the
Indians—Astronomy amongst the Chinese—The Emperor Chun’s Sphere
—The astronomers Hi and Ho put to Death for having neglected their
duty—A remarkable Antique Text—Astronomy amongst the Chaldceans
—Abraham as an Astronomer—The Book of Job—Astronomy 2000
' years before our Era—Ancient collection of Observations taken at Babylon
—The Egyptians and Astrology—The circular Zodiac of Denderah—The
great Pyramid of Gizeh, from an Astronomical point of view — The
Ptolemys, Kings of Egypt, Patrons of Sciences and Letters—Thales,
Anaximander, Anaxagoras, Pythagoras, Pytheas, Aristarchus, Aristotle,
Hipparchus, and his Catalogue of 1022 Stars—Julius Caesar, Sosigenes
the astronomer, and the learned Achoraeus—Pompey and the gifted
observer of silent Olympus—Ptolemy and his School—The Arabs and
Almagestes—Copernicus, his System, his Apprehensions, and his Swan-
- ' like Song-before Death—Galileo’s exclamation: “Oh! Nicholas Co-
pernicus !” — Tycho-Brahe and his System — Uranienburg — Descartes,
Philosopher and Savant—Newton and his splendid Discoveries.
I.
‘ Astronomy, as indicated by its Greek derivation (aonrjp,
star, vopos, law), is tbe science of the motions of celestial
Bodies. The purely descriptive part is often designated by the
names of Uranography and Cosmography. Its origin amongst
all nations is lost in antiquity; and this may be readily
understood, for the first impulse of man must naturally be
to observe the sky, the rising and setting of the stars,
bASTRONOMY.
their respective and varying positions, their relation to
the seasons, their diverse influences, &c.
Thus Bailly retraces the origin of this science to certain
antediluvian traditions, saved out of the general wreck; and
Josephus, in his Jewish Chronicles, cites, as an instance of
the attraction which the phenomena of the firmament pos-
sessed for the Patriarchs, the debris of a column which he
states to have been still extant in his time in Syria, and
upon which the descendants of Seth, third son of Adam and
Eve, had engraved, several centuries before the deluge, thb
leading results of their observations.
“ The spectacle of the firmament must,” says Laplace,
“ have taken the attention of primitive man, especially in
countries where the serenity of the air lent to the observa-
tion of the stars. In the pursuit of agriculture, he must
have needed to know the various seasons, and to be able to
prognosticate their recurrence. He would soon have dis-
covered that the rising and setting of the principal stars at
the moment of their plunging within the solar rays, or of
their emerging therefrom, facilitated him in his purpose.
Thus it is that we find the traces of astronomical observa-
tions dating back to such a remote period in the history of
every nation.”
India, the earliest civilized part of the Old World,
presents a subject of study replete with interest for any one
who will give it his special attention; and though I do not
pretend to possess any great knowledge of Hindoo astro-
nomy, it is impossible to doubt that this people was deeply
versed in this science, which was specially cultivated by the
guardians of the holy places. Cassini, Bailly, and Playfair
are of opinion that the Hindoosliave transmitted to US obser-
vations tafcen more than3000 B.c.7and though this date is
‘	’	-----------' >mlr ORIGIN AND PROGRESS OF ASTRONOMY.	3
contested by other eminent savarji^ thej all admit the great
antiquity oi^he docunients in»which these observations are
comprised#- Benthey, the moiFarHenT adversary of the
Hindoo pretensions, himself admits that their division of
the ecliptic into twenty-seven lunar stations must have, been
made in the year 1142 of our era; and this division could
only have been the result of a vast number of observations
extending over an immense period* The astronomical law
laid down by the Vedas for the arrangement of the calendar
must necessarily date back to the fourteenth century before
Christ, and Parasara, the first known Hindoo author who
wrote on astronomy, probably lived about the same time.
‘ It seems astonishing that the Hindoos, well versed as....ASTRONOMY,
4t
they were in science generally, should have been so ignorant- ,
in matters relating to our globe. Fig. 2 represents Mount:
Meroo, which, as they believed, formed the centre of the,
world. It was said to be a conical-shaped mountain, and
its sides to be covered with precious stones, its summit
being a sort of terrestrial paradise. This idea may have
been inspired by the sight of the lofty mountains* which
ran along the northern frontier of India; but,' for all that,
Mount Meroo has no existence save in the imagination
of the Hindoo mythologists. They supposed it to be -
surrounded by seven concentric belts of habitable lands,
divided from each other by seven oceans. The central
belt was said to comprise India, and to be surrounded
by a salt-\yater sea; the other belts being separatedr
ORIGIN AND PROGRESS OF ASTRONOMY.	5
'•froin .eacli other by seas of milk, wine, molasses,* &fc. In
^contrast to these errors, we find in the astronomical writings
of the Hindoos the proofs of a truly wonderful amount, of
learning.
/ To the Chinese we owe the earliest information upon
■ astronomy which has any claim to exactitude, From time
immemorial they have celebrated the epoch of the solstice,
in the hope of seducing the sun, by their dances and festi-
vities, to delay his departure towards the equinoxes; and,
though the first eclipses to which their annals allude are
only vaguely mentioned, they prove nevertheless that in the
time of the Emperor Yao, 2000 b.c., astronomy was made
the subject of special study. When Yao, whose reign had
been entirely devoted to the welfare of his subjects, died, at
the age of 118, they wore mourning for him during a space
of three years. “On the first day of spring (2255 b.c.)
Chun was installed as heir of the emperor in the hall of his
ancestors. Examining the instrument decorated with precious
stones which represents the stars and the movable tube which
enables one to obsewe them, he regarded the seven planets*
This done, he offered sacrifice to the Supreme Lord'of
Heaven, and went through the usual ceremonies in honour
of the six great spirits, as well as those usually performed
in respect of the mountains, the rivers, and the spirits
generally.” t
( ' This instrument,' representing the stars, was a sphere of
the heavens, termed Sicoun-Ki. The likeness of it is pre-
- served by the Chinese in several editions of the Chou-Kingr,
• * India, by MM. Dubois de .Tancigny and X. Raymond.
+ Chou-King, chapter 2.(5
ASTRONOMY.
and is accurately reproduced in Fig. 3. This sphere
represents the vault of the firmament divided into sections,
Fig. 3.—The Emperor Chun's sphere.
with the earth in the centre, and the gun, the moon, the
planets, and the stars in the places assigned to them in the
Ptoleimean system. If this sphere is really authentic, it
proves a high degree of astronomical knowledge for so
remote an epoch.*	,
The Chinese were acquainted with the use of the diai j
they measured time by the aid of the clepsydra. They*
4 Pautlner s Bistoiro do la Chino (Firmin-Didot).• ORIGIN AND PROGRESS OF ASTRONOMY. .	1
constructed instruments for measuring the angular distances
of the stars, and ascertained that the solar year, which they
made begin with the winter solstice, was about six hours
longer than 865 days. Their civil year was lunar, and, to
bring it back to the solar year, they used the period of
nineteen solar years,' which is equal to 235 lunations,—a
period exactly equivalent to that which Callippus, sixteen
centuries later, introduced into the Greek calendar. They
also divided the equator into twelve immovable signs and
twenty-eight constellations, in which they carefully assigned
the position of the solstices.
III.
Their estimates have been confirmed in the cases of
thirty-one out of the thirty-six eclipses, the elements of
Which have been handed down to us, and which they state
to have been observed between the years 776—480 b.c.
The Chou-ICing alludes to an eclipse of the sun which
occurred in the reign of Tchoung-King, who, in connection
with it, put to death Hi and Ho, two functionaries who
were at once astronomers and directors of religious cere-
monies. They were accused of preferring the pleasures of
the fable to the observance of their astronomical duties,
and it is interesting to cite the Chinese text bearing upon
this matter:—“At that time, Hi and Ho, abandoning
themselves to vice, neglected their duties,' they besotted
themselves with wine; they neglected the duties of their
office, and degraded themselves from their rank; they
createdconfusion in the celestial chain, and left their func-
tions unfulfilled. Upon the first day of the third moon of
autumn, the Tchin (a conjunction of stars) was not in
harmony with the constellation Fang (Scorpio). The blind8	ASTRONOMY.
man sounded the drum (the drummer was always a blind
man) ; the, magistrates and people assembled in haste,
like a horse let loose. Hi and Ho were like slaves at work,
they neither heard nor saw anything. Having become
unable to distinguish the. celestial signs and appearances}
they incurred the penalty decreed by the kings our prede-
cessors. . The Tchingtien says: - Whoso advances * *the
march of time shall be put to death; whoso retards it shall
also be put to death.*** *	• . * *	' r w
Father Gaubil, in his “ History of Chinese Astronomy,*-
fixes the date of this eclipse as fpr back as 2155 b .0.
In China an eclipse of the sun has always been looked
upon as a matter of importance to the State. Upon the
occasion referred to, the mandarins,' when the sun* was
suddenly veiled from their eyes, were obliged. to, repair in
hot haste to the palace, and to provide themselves with bows
and arrows to protect the emperor, who-is looked upon as
the image of the sun. The. bandmaster, who was a blind
man, sounded the drum, the mandarins offered presents in
honour of the spirit, whilst the emperor and court grandees
put on plain apparel, and remained fasting. The nature of
the laws edicted by the early kings against the calculators
who made a mistake in their observations indicates the
great antiquity of Chinese astronomy. It is also worthy
of notice that when the Chinese astronomers were merely
culpable of slight negligence, or a trifling miscalculation)
they were not visited with a heavier punishment than that
of fine> reprimand, or dismissal. .The punishment of death
was reserved for other misdeeds committed by the astro-
nomer-in-chief. t	■ r-t :
* Pautliier’s Eistoire do la Chine, pp. 58 and following (Firmin-t)idot).
t Father Gaubil’s Eistoire de VAstronomie Chinoise.9
, ORIGIN" and progress of astronomy.
V ' . '	.	IV.
<• The Chaldaeans come next, some of their observations
<• being said to date back to, nine centuries before Alexander
the' Great. When that monarch made his victorious entry
into Babylon in 381 b<c., some of the astronomers presented
.him with a series,of observations extending over 1903 years,
and dating back to the time of Nimrod. Calisthenes, who
^accompanied the Macedonian, sent them by his order to
•Aristotle. The latter tells that some observations still
more ancient were lost, and he mentions a circumference
"of the earth, the measure of which relates to the climate of
,Tartary; but he does not’ say how or by whom it had been
calculated, while the annals of. China explain the operation
^without giving the result. *’	'
Periods, which it must have taken centuries of observation
•to discover ahd calculate, were in use amongst the Chaldseans.
They were acquainted with the ancient planets; they pos-
sessed a zodiac divided into twelve constellations, and a
sphere which has served as a model to our own; they were
'also able to predict eclipses. Ptolemy testifies that they
had, from the most remote ages, been in the habit of
observing the occultation of stars by the moon, and that they
Were familiar with usage of sun-dials. They knew,'too,
the celebrated period called Saros, adopted by the Greeks,
'which includes about 18 solar years, 15 days, and 10 hours.
The recurrence of this period had the effect of bringing the
return of the eclipses upon the same day and in the same
order as in the preceding period. It is, the cycle which
Meton revealed to the Greeks, and the calculations of which
the Athenians caused to be engraved in letters of gold.
Bailly asserts that this period was taught to the Chaidseans
by a more ancient race; and it is remarkable that the same10
ASTRONOMY.
period was known to the Chinese, the Hindoos, and other
peoples being far apart, and, to all appearances, holding no
communication with each other. Yet, if we are to believe
the great majority of historians, the fertile plains of the
Tigris and Euphrates were the cradle of astronomy.
Abraham, born at Ur of the Chaldees, about 2040 b.c.,
is the starting-point of Jewish history; he knew the true
God, and led a holy life. The great Patriarch was always
famous in the East; the Chaldseans, his compatriots, con-
sidered him as one of their most eminent astronomers.
Need I cite that magnificent passage in the Book of Job ?
“ Canst thou bind the sweet influences of the Pleiades,
or loose the bands of Orion ?
'“Canst thou bring forth Mazzaroth in his season? or
canst thou guide Arcturus with his sons ?
“Knowest thou the ordinances of heaven? canst thou
set the dominion thereof in the earth ?
“ Canst thou lift up thy voice to the clouds, that abundance
of waters may cover thee ?
“ Canst thou send lightnings that they may go, and say
unto thee, Here we are ?
“Who hath put wisdom in the inward parts? or who
hath given understanding to the heart ?” * .
It is believed that Job inhabited Arabia, not far from the
borders of Chaldsea, inthe eighteenth century before our era.
M. Elie de Beaumont says The first astronomical
observations are lost in antiquity. The Chaldaeans were
possessed of certain notions, by no means inaccurate, as to
the stars, and the laws to which their movements are sub-
jected. For the last three thousand years astronomical
observations have been accumulating in enormous pro*
* Book of Job, chapter xxxviii. verses 31—3G.ORIGIN AND PROGRESS OP ASTRONOMY. ,11
portions, and becoming more precise. Tables of the results
attained have been compiled, each more perfect than the
preceding one, so that it is now possible to predict with
certainty what position each of the stars in the solar system
will occupy at a given moment. They supply the materials
for calendars and almanacs, the infallibility of which has
become proverbial.”*
The knowledge of astronomy soon spread from Chaldea
into Phoenicia and Egypt. The observations taken by the
Egyptians of the motion round the sun of the planets which
we call Mercury and Venus, proves how successful they
were .in this direction, and their priests were more par-
ticularly renowned; but under the name of. astrology,
.they made the movement of the stars to bear upon the
various events of life, and so claimed to foretell the future/
Thus it was in the sanctuary for the most part that
.the exact sciences were studied and perfected, an<f their
results made to serve some purpose of general useful-
ness. The astronomers were brought up to the priest-
hood, and. the vast platforms (or flat roofs) of the temples
were useful as observatories. Their observations in time
taught them that the rising of the same stars ceased,
after the lapse of several centuries, to correspond to the
same seasons, and they noticed their change of position.
They divided the heavens into constellations, the names
and figures of which were taken from Egyptian subjects.
They constructed a zodiac which is thought to have been in
existence earlier than 2500 b.c. The civil calendar was
arranged, the year being composed of 365 days, which
were divided into twelve months, each of thirty days, and
* Elie de Beaumont's Moge. Historique de Jean Plana, read before the
Academic des Sciences, November 25tli, 1872'.H	ASTRONOMY.
followed by five supplementary days. They also made use
of the week, or period of seven days.*
V.	‘	?
Astrology, as I have remarked, was in vogue amongst the
Egyptians, as is to be proved from the zodiacs which haye
been handed down to us. Fig. 4 is a miniature engraving
of the circular zodiac of Denderah.f At first sight it seems
to. be nothing more than a conglomeration of various figures
surrounded with sacred letters; but on closer inspection we
notice an outer circle, with an inscription traced in. sacred
letters, and intersected at equal distances by figures with the
head of a Woman looking upwards, or that of. a hawk in. a
reclining posture. These figures, their arms raised aloft, hold
up a shield entirely covered with signs of various kinds. To
the l^Ffc, a little below the centre of this shield, which repre-
sents the firmament, is seen a lion, followed by a woman and
treading upon a serpent—this is the zodiacal sign of Leo.
Behind this group is a woman holding in her hand a wheat-
ear—this is Virgo. We then notice, going from/the right to
left, Libra with its two scales; Scorpio, Sagittarius, in the
shape of a winged centaur; Capricorn, half goat half fish;
Aquarius, pouring water out of two vessels; the Pisces, con-
nected with each other by triangular lines; next to them
Aries, Taunts, and the Gemini, which represent two men
walking in company; and, in succession, Cancer just above
the head of the Lion. Leo is the first sign ip this system of
the zodiac; within and beyond the spiral line formed by the
twelve signs, come the chief extra-zodiacal,constellations,
and as the gigantic animal, moving on its hind legs near the
\	* Egypte, by Cliampollion-Figcac, p. 95.	~	-	•?
t See JRccherches siir VEgyptc, by Latronne.	,ORIGIN'AND PROGRESS OP ASTRONOMY, 13
centre of the disc, has been generally admitted to represent;
what we know as Ursa Major,-'-the North Pole must be
placed in close proximity to this figure. The discovery of,
the Benderah and Esnah zodiacs * led to very fierce discusr.,
sions, which, however, need not be referred to in these pages. .
Tlie pyramids are very remarkable from an astronomical
point of view; they represent the most ancient monument
of human skill in the known world. The largest, that of
(jizeh, is the most carefully constructed, being so built
that each of its four corners faces exactly one of the four
cardinal points. Even in the present day we should find it
difficult to trace so vast a meridian without deviating a.
■	* See Eecherchcs mr VEgyptc}by Latronne, p. 14.ASTRONOMY.
14
single fraction. From this situation of the great pyramid
has been drawn the conclusion, very important as bearing ,
on the physical history of the globe, that the position of the
earth’s axis cannot have varied to any perceptible extent
for thousands of years, It may be added that the great
pyramid is the only monument in the world which, from its
antiquity, is capable of supplying the means for ascertaining
such a fact. The appended illustration, after Champollion,
represents the present appearance of this pyramid and of
the Sphynx, which stands in close proximity to it.
Pig. 5.—The great Pyramid of Grizeh and the Sphynx
The encouragement offered by the Ptolemys—more espe-
cially by Ptolemy Philadelphus—to science and art, gave a
great impluse to the development of intellectual knowledge.
We know that the latter king* attracted to his capital the most
learned men in Greece, that he lodged them in his palace,ORIGIN AND PROGRESS OP ASTRONOMY. 15
and furnished them with every facility for carrying out their
scientific studies and researches.
:	yl	; .
- The Greeks did not cultivate astronomy until long after
the Egyptians, whose pupils they were. In the year 640
b.c. Thales of Miletus .went to Egypt to study, and he
afterwards founded the Ionian school, in which he taught
the spherical shape of the earth, the obliquity of the
ecliptic, and the causes which superinduce eclipses of the
sun and of the moon. After him came Anaximander and
Anaxagoras, to the first of whom is credited the invention
* of the dial, the terrestrial globe, and geographical charts.
Soon after, this school produced Pythagoras of Samos, a
pupil of Thales, who made several journeys to Egypt and
India. On his return home he was driven into exile, and
went to Italy, then called Greece Major, where he founded
the. school named after him. In addition to the subjects
taught by the Ionian school, he expounded the two distinct
motions of the earth, one upon its own axis and another
round the sun. He asserted that the stars were suns, the
centres of so many planetary systems. Thus we see that
the fundamental principles of the astronomical system now
universally accepted were in general use five hundred years
before the birth of Christ.
From the time of Pythagoras it was maintained that the
regular movement of the celestial bodies through space
produced an ineffable harmony which was termed the har-
mony of the spheres. In the first place, the aspects were
held to have an affinity with the intervals of the tones.
Thus, the quadrate aspect, or the quadrature, is, as com-16	.	ASTRONOMY.
pared to the sextile aspect, or 60 degrees, as 8 is to 2—this ,*
is the affinity which forms the fifth (quinte) in music...
Kepler himself endeavoured to establish a relation between
the distances of the planets from each other and the inter-
vals of music; but these comparisons are very arbitrary and
incomplete* In proportion as the theory of music has been
made more perfect,* the ideas formed as to this harmony,
have undergone great modifications. It was supposed that:
the moon, as the lowest of the planets, that is, the nearest,
to us, answered to the note mv Mercury to fa, Venus to
sol!, the Sun to la, Jupiter to ut, Saturn tope; and the orbit,
of the fixed stars, as being the most distant (or highest) of.
all, to. mi or to the octave.
The'most celebrated astronomers, after Pythagoras, were *
Pytheas, who taught the way to classify climates by the:
length of the days and nights; Aristarchus of Samos, who
fixed the apparent diameter of the sun in the year 281 b.c., -
and calculated the distance of that planet from the earth;/
and, thirdly, Aristotle> the disciple of Plato, who set himself
to ascertain, by a series of astronomical observations, the*
shape and size of our planet.
" They were followed by Hipparchus of Bithynia, who-
acliieved great renown in the celebrated sohool of Alex- *
ahdria 140 years b.c. This great astronomer, looking upon*
previous researches as unreliable, determined to go over the
whole ground afresh, and to admit as genuine only those
\vhich should be confirmed by his own expedience. He
fixed to a nicety the extent of the tropical year, discovered
the precession of the equinoxes, and it is to him that we:,
owe the use of latitudes and longitudes. A new star having:
suddenly appeared, he composed a catalogue of 1022 dif-
ferent stars, which he calculated f6r the 128th year beforeORIGIN AND PROGRESS OF ASTRONOMY.
17
the Christian era. This Pliny terms “ an enterprise worthy
of the gods, for Hipparchus thus afforded the means for
ascertaining hereafter whether certain stars disappeared,
and whether they underwent a change of position, size, or
light; he left, in fact, the heavens as an inheritance to
those who should come after him, and who possessed suffi-
cient genius to turn his labours to good account.”
There was an interval of about three centuries between
Hipparchus and Ptolemy, to whom I shall presently refer.
During this period there was no lack of astronomers who
made discoveries of more or less value. It was at this
time, indeed, that Poseidonius discovered the causes of the
ebb and tide in the sea, and that the calendar underwent
“the Julian reform,” as it was termed, by Julius Caesar,
who initiated it, entrusting the work to Sosigenes in the
year 46 b.c.
Eudoxus fixed the duration of the year at 365£ days,
which was admitted as correct by Sosigenes, and adopted
in the Julian calendar. The Julian year lasted 365, and,
once in four years, 366 days, which caused a miscalculation
of one day every 134 years. This mistake was set right in
the Gregorian calendar.*
YII.
History tells us that Julius Caesar was an ardent lover
of the sciences, astronomy in particular. In his interview
with the learned Achorseus, he is reported to have said :—“ I
came to Egypt to encounter Pompey, but your renown was
not altogether foreign to my determination. In the midst
of war, I have always studied the movements in the heavens,
* See Chapter 16, on the iHvision of Time.
018
ASTRONOMY.
the course of the stars, and the secrets of the gods. My
arrangement of time is at least equal to the fasti of Eudoxus,
&c.” Achorseus, in reply, alluding to the ideas then preva-
lent as to the solar system, pointed out that “ the stars
which alone modify the volitation of the heavens, and which
extend towards the pole, are supposed to possess varied
influences. The sun divides the year into seasons, regu-
lates the interchange of day and night, holds the stars
captive by the power of its rays, and limits their wayward
course to its centre. The moon, with its varied phases,
mingles the land and the sea. Saturn influences the cold
regions and the snowy zone; Mars, the winds and the
thunder; Jupiter, the air and the unchanging ether; the
productive Venus preserves the germ of universal life;
Mercury is supreme over the vast expanse so soon as it
reaches the region of the sky, where the constellation of
Leo is lost in that of Cancer, where Sirius pours forth his
darting fires, where the changing cycle of the year is
effected in (Egoceros and Cancer, mysterious witness of the
sources of the Nile.”	j
We know that Caesar took a real interest in astronomy,
and that he wrote a treatise about it. Pompey, too, was
attracted by this science. Leaving Lesbos, bowed down by
grief at the defeat of his army, and looking with apprehen-
sion at the future, he endeavoured to find distraction from
his cares in a conversation with the pilot, and his mind
became partially reassured by contemplation of the starry
sky :—“ He then talked with the pilot about all the stars,
inquired how he ascertained the approach to land, and the
means of measuring by the heavens the distance which the
ship had accomplished; what stars indicated Syria and
Libya. The pilot’s answer was that he and his fellowsORIGIN AND PROGRESS OP ASTRONOMY.
19
never allowed themselves to be guided by a star slowly
declining in the firmament, for they would only deceive the
sailor, who preferred to trust the never-setting axis which
receives light from the twofold Arctos..........”
VIII.
The remainder of astronomy may be divided into five
leading systems—those of Ptolemy, Copernicus, Tycho-
Brahe, Descartes, and Newton. Ptolemy was a celebrated
mathematician. He was bom at Pelusium, though Theodoras
Meliteniotes states that he was a Thebain, and that he first
saw the light at Ptolemais, the capital of that province. At
an early age he went to Alexandria, where he founded a
school, which enjoyed great celebrity about 175 b.c. En-
dowed perhaps with more application than genius, he
collected and arranged the works of his predecessors, espe-
cially those of Hipparchus, and though he did not correct
all their mistakes, he was nevertheless the greatest astro-
nomer of his day, and his definite system has continued to
be named after him. These his labours have been pre-
served to us by the Arabs in a well-known work Called the
Almagestes.
His theory was, that the world is composed of two
regions: the elementary and the ethereal. The first com-
prised bodies which the ancients regarded as the four
elements: to it, the earth, motionless, in the centre of the
world; water, covering a great part of the earth’s surface;
air, which is above the earth; and fire, which is above the
air.
The ethereal region, surrounding the elementary region,
was composed of eleven skies, which revolved around the20
ASTRONOMY.
earth as around a common centre. Beyond the eleven shies
was the empyrean, or abode of the blest. All the celestial
bodies moved around the earth, which was motionless in
the centre of the world.
This system lasted more than fourteen hundred years.
He had an ingenious explanation of the positions and retro-
gradations of the celestial bodies, for an epoch when no
conception had been formed as to the immensity of the
heavens and the enormous distance of the stars.
IX.
Copernicus was bom at Thom, Poland, in the year 1472,
and he died in 1543. It redounds to his fame that he was the
son of a Polish baker, and that by the unaided force of his
own genius he raised himself to the highest rank as a savant.
He visited Italy in order to consult with the most famous
astronomers, and, after spending some time at Borne as a
teacher of mathematics, returned to Frauenburg, in his
own country, where his uncle, who was a bishop, provided
him with a canonry.
Copernicus submitted all the then known systems of
astronomy to the test of a fresh examination. He disco-
vered the germs of the system which bears his name in
the researches of several ancient astronomers, Philolaus
more especially; but he made it really his own by the
application of countless observations and calculations.
Apprehensive of contradiction, he did not publish his ideas
till towards the close of his life, and did not, in fact,
receive a copy of the book in which they were embodied
until the day of his death. G. Donner, in a letter to the
Duke of Prussia, says that “ the honourable and worthyORIGIN AND PROGRESS OP ASTRONOMY.
21
Dr. Nicholas Copernicus has let his work appear a few days
before his departure from earth, like the death-dirge of the
swan.”
Fontenelle deems Copernicus happy in the period of his
death. “ Copernicus,” he writes, “ was himself very appre-
hensive as to the reception which his ideas would meet
with. For a long time he was unwilling to publish them,
and only yielded at last to the solicitations of some persons
of influence. But what did he do on the very day that he
received the first copy of his book in print ? Why, he died,
and so cleverly avoided the shower of contradictions which
he foresaw as certain to be brought forward.”*
The lines in which he gives utterance to his doubts will
be read with interest:—“ I was long in doubt as to whether
I should publish my commentaries upon the motions of
celestial bodies, or whether it would not be better to imitate
the example of certain followers of Pythagoras, who, instead
of committing their ideas to writing, imparted them ver-
bally, communicating them to the adept, and to those who
felt an interest in the mysteries of philosophy, as may be
gathered from the letter of Lysis to Hipparchus. This
they did, not as some surmise, through an excessive spirit
of jealousy, but in order that the gravest of questions,
which had been deeply studied by men of undoubted capa-
cities, should not be made sport of by the idlers, who have
no taste for serious works which bring no gain with them;
or by men of limited intelligence, who, giving themselves
up to the nominal study of science, make their way into
the midst of the philosophers like drones amongst bees.
The more I hesitated and resisted, the more my Mends
* Fontenelle’s Pluralite dcs Jlfondes,33
ASTRONOMY.
pressed me. Nicholas Schomherg, Cardinal of Capua, a
man of deep erudition, and my most intimate friend Tide-
man G-ysius, Bishop of Culm, as well read in the Scriptures
as he was learned in the sciences, were specially urgent in
their appeals. The latter put so much pressure upon me
that at last I agreed to publish the wort which fox- seven-
and-twenty years I had kept to myself.”
Fig. 6.—Portrait of Copernicus, engraved by J. Falck.*
In Copernicus’ system, the sun is motionless in the
* The portraits of Copernicus and the three which follow are from the
collection of M. Ambroise Firmin-Didot.ORIGIN AND PROGRESS OP ASTRONOMY, 23
centre of the universe, the earth is classed amongst the
planets, the moon is one of the earth’s satellites; all the
planets revolve around the sun, which is the general centre
of the universe; they traverse, at different times, orbits
, oval or elliptical.
' The earth is subject to three motions, which explain
the annual and daily motions of the heavens. The first,
one of rotation upon its axis, is from west to east, describing
the equinoctial circle in the course of the day and night.
One effect of this rotation is, that the sun and the stars,
though motionless, seem to rise and set each day, and to
follow a fixed inclination from east to west.
The second is an annual motion of the earth round the
sun, by which, in the space of 865 days 16 hours, it
accomplishes its course in the ecliptic circle, but in the
inverse direction to the order of the signs; that is to say,
that when itself in Capricorn, the sign of the zodiac which
answers to winter, it sees the sun in the summer sign,
Cancer, and is in the summer season. When it corresponds
to Cancer, it sees the sun in the winter sign, Capricorn,
and is in the winter season.
The third is a motion of the earth upon itself, by which,
while keeping its axis continually turned towards the same
point of the sky, it successively exposes each part of its
surface to the sun in the course of the year.
These two latter motions, combined, are the cause of the
unequal length of the days and nights, and the vicissitude
of the seasons.
Copernicus is compelled to place the stars at an incalcu-
lable distance, because the earth traverses each year, in
its v revolution round the sun, an orbit of more than
599,581,708 miles; so that, at the end of six months,u
ASTRONOMY.
it must be nearly 209,853,595 miles distant from the
spot where it then was. This is of no consequenoe, and
does not prevent his system, established upon a mathe-
matical basis, from being the simplest, the most] natural,
and the truest in the world. Copernicus must, therefore,
be looked upon as the founder of modern astronomy.
His contradictors said“ If it were true that the sun was
in the centre of the planetary system, and that Mercury and
Venus revolved around it, in an orbit nearer to it than that of
the earth, these two planets would have phases of their own.
When Venus is on this side of the sun, she would have a
crescent shape, like the moon going down at night; when
she forms a right angle between the sun and us, she would
be in shape like the first quarter of the moon. And yet
such a thing is never seen.*0 Copernicus* reply was that
such undoubtedly was the case, as would be seen some day
if instruments could be brought to a sufficient degree of
perfection. And so it happened at Florence seventy years
later. Galileo, exploring the heavens with a newly-con-
structed glass, in the end of September, 1610, perceived
that Venus had phases like the moon. He could not
restrain the ejaculation, “ Oh I Nicholas Copernicus, could
you but have lived to enjoy this recent discovery, which so
fully confirms your ideas! ”
X.
Tycho-Brahe was born at Scania, in 1546, and belonged
to one of the noblest families in Denmark. From infancy
he displayed a strong taste for astronomical observations.
He travelled all through Germany and Switzerland to visit
the different observatories and learn the methods then in
use, and he was entrusted with this mission by the King ofORIGIN AND PROGRESS OF ASTRONOMY.
25
Denmark, wlio gave him the Island of Huen to take his
observations. There he built the celebrated observatory
Fig, 7.—Portrait of Tyclio-Brahd, engraved by de Gheyn.
which he called Uranienburg, residing there for seventeen
years. At the death of the ting, his successor, Frederick,ASTKONOMY.
showed him less favour; so he left Denmark, and proceeded
to Bohemia, where the Emperor Joseph II. afforded him a
permanent hospitality. He died at Prague in 1601. To
him we owe numerous observations, the fruit of his twenty
years’ residence in the Island of Huen, and many of them,
marvellously exact, have assisted Kepler to his discoveries.
When a new star appeared in Cassiopea, in 1572, Tyclio-
Brah^ compiled a catalogue, in which the , position of
more than a thousand stars was fixed with a precision
most remarkable at a period antecedent to telescopic
observation.
Tycho-Brahe attempted to upset the system of Coper-
nicus, then in great repute, and to connect it with that of
Ptolemy; wherein, of course, he failed. He maintained
that the distance from the fixed stars to the sun, as laid
down by Copernicus, was very improbable; and, desirous,
of upholding certain Scriptural passages which were incor-
rectly said to contradict this system, he re-established the
eartli in its old position, placing it motionless in the centre
of the world, and making the moon, the planets, and fixed
stars revolve round the sun, while the latter in turn moved
round the earth with all its planetary cortege. Thus he
was one with Copernicus in looking upon the sun as the
centre of the constellations we have named, and with
Ptolemy in holding that the earth is motionless, the sun
and the stars revolving around it.
In this hypothesis Venus and Mercury pass, during part
of their revolution, between the sun and the earth, which
, explains pretty correctly their phases, as seen through a
glass, which are very like those of the moon. This system,
' though it did credit to Tycho-Brahe’s ingenuity, was univer-
sally rejected.ORIGIN AND PROGRESS OE ASTRONOMY. S7
XI.
Descartes, the great French philosopher, was born at
Lahaye (Touraine) in the year 1596. In early life he
followed the profession of arms, serving as a volunteer
under Maurice of Nassau and the Duke of Bavaria; but
he soon left the service. He then travelled through Ger-
many, Holland, and Italy, and paid several visits to Paris,
where he formed the acquaintance of several scientific men.
After remaining for several years undecided as to the choice
of a career, he resolved to give himself up to solitary study,
and for this end left France for Holland, where he lived
for some time in the strictest seclusion.
Descartes’ works earned him great renown, but they also
drew down upon him many contradictions, and even per-
secution.
The Princess Elizabeth, daughter of the Palatine Elector
Frederick V., delighted in his society. Mazarin gave him
a pension of a thousand crowns, and Queen Christina
invited him to reside at her Court. Flattered by this
request, Descartes went to Stockholm, in the winter of
1649, but he died there a few months later from the severity
of the climate, at the age of fifty-four. His remains were
brought back to France in 1667, and entombed with great
ceremony in St. Genevieve.
He is looked upon as the father of modern philosophy.
To him we owe the application of algebra to geometry; he
first discovered and proved the existence of the centrifugal
forces, which maintain the universal equilibrium by balancing
in all directions the action of gravity. His system, gene-
rally known as the vortices of Descartes (tourbillons de
Descartes), is very similar to that of Copernicus.28
ASTRONOMY.
The word vortex, thus used, is intended to signify a
certain quantity of matter divided into an infinity of very
small particles, which revolve all together around one com-
mon centre, while each one of them revolves round a centre
of its own. For instance, applying this kind of motion to
the stars, the vortex (tourbillon) in which we are placed
is composed of the sun and the planets which revolve
around it, as they do also upon themselves. Descartes
Fig. 8.—Portrait of Descartes, engraved by Jonas Suyderhoeff.
admits three lands of celestial bodies—1st; the fixed stars,
all of which are suns; 2nd, the planets, which revolve*ORIGIN AND PROGRESS'OE ASTRONOMY. 29
round the suns; 3rd, the moons, which revolve round the
planets.
j ' This system did not come scathless out of the analytic
examination to which he himself subjected it, but this great
thinker, by his creative researches and fruitful discoveries,
gave a great impulse to human thought, and a spur as deep
as it was durable to science and philosophy.
XII.
Newton, the most illustrious of English savants, was
born in the year 1642, at Woolstrop, Lincolnshire. He is
placed in the first rank of mathematicians, natural philo-
sophers, and astronomers, yet it may be said that his dis-
coveries were, to a certain point, led up to by Descartes.
His mother had intended to make a farmer of him, but as
he showed no aptitude for this calling, she allowed him to
follow his own inclination. He was sent, at the age of
thirteen, to Cambridge, where Dr. Barrow was his mathe-
matical tutor. He soon learnt more than his tutor knew,
and made his greatest discoveries in mathematics before he
was three-and-twenty; in particular that of the binomial
named after him, and of the infinitesimal calculation which
he called the calculus of fluxions (differential calculus).
• In 1665 he left Cambridge, in consequence of the plague,
and returned to Woolstrop, where, it is said, he saw the
apple fall, which led to his first ideas as to universal
gravity and the system of the universe.
f It seems that in 1692; his reason momentarily gave way,
either as the result of a fire which destroyed several of his
papers, or because he had laboured too hard, and after that
time he did not publish any original work of importance,30
ASTRONOMY.
contenting himself with a revision of previous publications.
In 1699 the French Academy of Sciences elected him a
foreign associate, and in 1703 the Royal Society chose him
as President—which title he retained until his death. His
Fig. 9.—Portrait of Newton, engraved by J. Smith.
latter years were embittered by a dispute in which he was
engaged with Leibnitz, whom he accused of plagiarism, the
result of which was that, while Newton was admitted to
have the priority, Leibnitz, on the other hand, proved that
he had also made the self-same discovery.
An English poet has termed him a man of pure intelli-ORIGIN AND PROGRESS OF ASTRONOMY. 31
gence, sent to man by the Creator to explain the works
which He had created.
His profound knowledge of mathematics led him to the
discovery of the curve described by a body in its revolution
round a* centre, to which it is attracted by a force propor-
tional to the mass of the central body, and decreasing
according to the laws of gravity. He thus ascertained
that all the celestial bodies revolve in the four principal
curves of the conic sections, viz., the planets in ellipses,
the satellites in circles, the comets parabolically or hyper-
bolically.
The summary of his system is this: Just as all weighty
bodies gravitate to the earth’s centre, so do the bodies
which compose the universe gravitate, by the force of
attraction, towards the sun, which is their common centre.
But as the planets, if they were only governed by the force
of attraction, that is to say, by the force which the sun
exercised in attracting them towards itself, they would
gradually be drawn into that celestial body. Newton
adduced two moving powers given them by the Creator at
the beginning of the world, the first of which was a centri-
petal force impelling the planets towards the sun; the
second a centrifugal force, which hurried them away from
it, the one counterbalancing the other.
Thus the earth, instead of being carried far away from
the sun by the centrifugal force, is maintained, by the action
of the two combined, in its orbit, and compelled to describe
around it an ellipsis of which it occupies one of the foci.
Newton also calculated the 'motions of the satellites
and the routes followed by the planets with an. accuracy
confirmed by subsequent observations.
The flood and ebb of the sea, the precession of the equi-3£	ASTRONOMY*
noxes, the nutation of the earth’s axis, the difference
between the true and the mean time, are but effects
evolved from the law of universal gravitation.
In the course of this work I shall have an opportunity of
developing ideas which can only be glanced at in a rapid
review of the history of astronomy.CHAPTER II.
THE SOLAR SYSTEM.
The Sun—The eight principal planets—The smaller planets—The satellites—
Formation of the solar system.
I.
The Sun, and its cortege'oi orbs, which do not emit any
light of themselves, constitute what we call the solar system.
It is composed, firstly, of the Sun, which, for astronomical
purposes, is generally designated by the sign ©, the diameter
of which is 108 times that of the Earth, and which revolves
upon its own axis once in about 25 days, 10 hours;
secondly, of eight principal planets, and 128 smaller or
telescopic planets, the orbits of which are embraced between
those of Mars and Jupiter, at about co-equal distances from
the Sun.
The principal planets, enumerating them according to
their increasing distance from the Sun, have been called:—
1st, Mercury, represented by 9, whose mean (listance
from the sun is 35,893,000 miles, with a revolution round
that luminary of 87 days, 23 hours, 15 minutes, and a dia-
meter two-thirds that of the Earth.
2nd, Venus, 9, with a mean distance from the Sun of
66,130,000 miles, a revolution of 224 days, 16 hours,
48 minutes, and a diameter nearly equal to that of the5
Earth.ASTRONOMY.
3rd, the Earth, ©, with a mean distance from the Sun of
91.430.000	miles, a revolution of 365 days, 6 hours,
9 minutes, and a diameter of 7,901 miles.
4th, Mars, <J, with a mean distance from the Sun of
139.312.000	miles, a revolution of 686 days, 23 hours,
31 minutes, and a diameter half that of the Earth.
5th, Jupiter, %, with a mean distance from the Sun of
475.693.000	miles, a revolution of 4,332 days, 14 hours,
2 minutes, and a diameter eleven times that of the Earth.
6th, Saturn, T?, with a mean distance from the Sun of
872.135.000	leagues, a revolution of 10,759 days, 5 hours,
16 minutes, and a diameter nearly ten times that of the
Earth.	' ?
7th, Uranus, ty, with a mean distance from the sun of
1.752.851.000	miles, a revolution of ,30,686 .days, 17 hours,
21 minutes, and a diameter four times that of the Earth.
8th, ‘Neptune, T, with a mean distance from tile Sun of
2.746.271.000	miles, a revolution of, 60,118 days, and a
diameter nearly five times that of the’ Earth.
The solar system is further composed of 21 planetary
satellites: 1 for the Earth (the Moon, represented' by the
figure ®); 4 for Jupiter, 6 for Saturn, 6 for Uranus, 2 .for
Neptune, and comets the 'number Of which increase every
day.
Kepler suspected the existence of a planet between Mars
and Jupiter, and Father Secchi says that he was the-first to
discover a certain regularity in the distribution of the
planets. There seemed, however, to be some anomaly in
the distance which separated Mars from Jupiter, and, upon
this ground, he predicted that some hitherto unknown star
would eventually be discovered in the space between them :
a prediction which was more than verified two centuriesTHE SOLAR SYSTEM.
35
afterwards,* for no less than 128 have already come under
observation, as will he seen by the appended table, and
fresh ones are being discovered every day. M. Le Vender
has calculated that they are not, put together, equivalent to
a body one-third the size of the Earth, for he argues that if
they were larger than that their attraction would have led
to greater variations in the motions of the perihelion of
Mars than have hitherto been noticed.f
II.
MINOR OR TELESCOPIC PLANETS BETWEEN MAES AND
JUPITER.
(?) Ceres.	@ Proserpine.	0 Nemausa.
0 Pallas.	@ Euterpe.	0 Europa.
@ Juno.	as) Bellona.	0 Calypso.
(T) Vesta.	0 Ampliitrite.	0 Alexandra.
(T) Astreea.	0 Urania.	0 Pandora.
@ Hehe.	0 Euphrosyne.	0 Melete.
@ Iris.	0 Pomona.	0 Mnemosyne.
@ Flora.	0 Polyhymnia.	0 Concordia.
Q Metis.	@ Circe.	0 Olympia,
0 Hygeia.	0 Leucotlirea.	0 Danae.
PartlienQpe.	0.Atalanta.	0 Echo.
0 Victoria.	@ Ficles.	0 Erato.
0 Egeria.	0 Leda.	0 Ausonia.
0 Irene.	0 Leetitia. .	0 Angelina.
0 Eunomia.	0 Harmonia.	0 Maximiliana,
0 Psyche.	0 Daphne.	0 Maia.;
0 Thetis.	• 0 Isis.	0 Asia.
0 Melpomene,	0 Ariadne.	0 Leto.
0 Fortuna.	0 Nysa.	0 Hesperia.
0 Massilia.	0 Eugenia.	0 Panopca.
@ Lutetia.	0 Hestia.	@ Nioho. .
@ Calliope.	0 Agla'ia..	. 0 Feronia,
@ Thalia.	0 Doris.	0 Clytie.
0 Themis.	0 Pales.	0 Galatea.
@ Phocea.	0 Virginia.	' 0 Eurydice.
. * Father Sccclii on The Sun.
t Volume xxxvii. p. 793, of the Journal of the Academic des Sciences, p. 334..
d236
ASTRONOMY.
© Freia.	@ Aurora.	© Ipliigcnia.
@ Riga.	0) Arethusa.	© Amaltliea.
@ Diana.	© iEgle.	© Cassandra.
@ Eurymonc.	(97) Clotlio.	©
© Sappho.	© Iantlie.	© Sirona.
© Terpsichore.	(99) Dike.	© Lomia.
© Alcmeno.	0 Hecate.	©
@ Beatrix.	@ Helena.	©
@ Clio.	© Miriam.	©
© Io.	© Hera.	
@ Semelo.	© Clymeno.	©
© Sylvia.	@ Artemis.	©
© Thishe.	© Sylvia.	@
© Julia.	© Camilla.	©
© Antiope.	© Hecuba.	©
© Egina.	© Felicitas.	©
0 Undina.	© Lydia.	©
© Minerva.	© Ate.	
Planets 115, 118, and the remainder have not yet been
named.
III.
The revolution of the Earth round the Sun, &c., &c., is
now well known; but what is not so generally known, and
what creates some surprise amongst novices, is that the
solar system, that is to say, the Sun and the Earth, the
planets and the moons, have an incessant tendency to shift
towards the constellation of Hercules.
Herschel proved that the apparently inextricable irre-
gularities of so many special stellar motions are mainly due to
the displacement of the solar system; and that the point in
space, towards which we are advancing each year, is situated
in the constellation of Hercules. These results are mag-
nificent. The discovery of the specific movement of our
system will always count as one of Herschel’s greatestTHE SOLAR SYSTEM.
37
achievements, notwithstanding the previous conjectures of
Fontenelle, Bradley, Mayer, and others. In juxtaposition
to this great discovery must be placed another which seems
destined to yield still more magnificent results, and which
was given to the world in 1803. I refer to the discovery
that certain stars are reciprocally dependent, connected
with each other as the planets of our system and then
satellites are to the Sun.*
Father Secchi .has set forth in such simple yet clear
terms, the ideas generally accepted as correct by modern
science concerning the formation of the solar system, that
we cannot do better than quote him:—
“Astronomers of the present day are agreed that our
solar system is due to the condensation of a nebula, which
formerly extended beyond the limits now occupied by the
most distant planets. This nebula was originally endowed
with a slow rotatory motion, which must have gradually
become accelerated. According to a law of mechanics, known
as the law of superficies, every disengaged particle must move
in such a way that its radius-vector will describe equal
superficies at equal intervals; whence it follows that, the
radius being gradually lessened by progressive contraction,
the arc described during the unity of time must have in-
creased, so as to keep the superficies from undergoing
variation. An augmentation of centrifugal force results
from this increase of speed, and when this force comes to
equal the force of gravitation, rings are formed which
remain suspended around the central mass. As the speed
goes on increasing, these rings are broken, and the different
fragments, each one in obedience to the laws of attraction,
* Astronomic Populaire.ASTRONOMY.
38
in ' their turn form new masses which are isolated from each
other, -and whibh become centres of action similar to the
principal centre. -These masses have in turn been sur-
rounded by rings of a secondary order, some of which are
still in existence, while others, getting dispersed, have gone
to form satellites.
“ This theory* expounded by. Kant, Herscliel* and Lap-
lace, lias been confirmed by the ingenious experiments of
M. Plateau. A mass of oil poured into a mixture of water
and alcohol of the same density as itself, will be seen to
assume the spherical shape which molecular attraction
would tend to give; it. If it is made to turn around its
vertical diameter at an increased rate of speed, the sphere
will be found first to flatten, and after a certain time to
detach a ring similar to that of Saturn. As the speed is
still further increased, the ring will be broken up, and form
into small spheres revolving upon their own axis and
around the main mass.	...
“ The matter which composed the primitive nebula must
have been far more rarefied than that which we are able to
obtain with the best of pneumatic machines, and has since
become enormously contracted and condensed, leaving the
planets and the satellites at various distances. The Sun is
the still incandescent and gaseous residue of the primitive
mass. We find in the sidereal world traces of this forma-
tion, in our planetary world, the rings around Saturn, in
the stellar world, the annular nebulse. These masses are
composed of a matter which is still gaseous, and they seem
to constitute worlds in course of formation.” *
. M. Inrichs arrives at the important conclusion that the
* Father Secchi on The Sun, p. 332. Also Vestiges of Creation.THE SOLAR SYSTEM.
39
law of progressive condensation is bound up with the third
law of Kepler, and that the latter is itself the outcome of
universal gravity - acting in direct ratio with the masses
and in inverse ratio with the square of the distances. Thus
the law as to the formation of the. planetary system would
be but a consequence of universal gravity.
M. Delaunay, of the French Institute,, also remarks:
“ The great law of universal gravity, which we owe to the
genius of Newton, has introduced unity into the science of
astronomy, and enabled us to attach to one particular cause
all the peculiarities presented by the motions of the
celestial bodies.” *
* Rapport sur leprogres do VAstronomic, p. 1.
Fig. 10. —Urania, antique statue, now in Sweden.CHAPTER III.
LIGHT AND THE DETAILS OF SPECTRUM ANALYSIS.
Light enables ns to recognise the stars—Revelations by spectrum analysis—
Hypothesis of the emission, and that of undulations—Laws of light—
Various measurements of its speed—The solar spectrum—Chemical action
of light—Length of luminous waves—Analogy between sound and light—
Molecular vibrations and atomic vibrations—Mode of propagating light—
Refraction and reflection—Luminous interferences—How light added to
light produces darkness—Triumphal entry of the spectrum analysis into
science—Its history—Metals revealed by analysis of the spectrum which
they elicit during combustion—Important chemical and spectral laws—
Curious experiments in physiology — Undreamed of horizons in astro-.
nomy—Ignition in the celestial domain — Spectra of planets, moons,
and stars—Substances discovered in the stars — Nature of nebula}—
Movements of the stars revealed by their spectra—Discovery of the
nature of comets—Matter following in the track of the aerolites—Unity
of composition extending to all the luminaries in the universe—The
inhabited celestial spaces,
I.
It is light which reveals to us the stars, and therefore it
is by its aid that we must commence our study of them*
Spectrum analysis has opened up a new field to astronomy,
and laid bare horizons of which no one had ever dreamed.
It is wonderful to reflect that a mere ray of light, that is to
say, an imperceptible movement communicated to ether
in boundless space, is transformed, by the aid of modern
science, into a telegram sent from the worlds of the infinite
to instruct us, not only as to the nature of the elements
which compose them, but as to the motions which hurry
them through space, and which we should be unable to
ascertain with the most perfect of telescopic instruments.LIGHT.
41
These revelations, exceeding all that the wildest imagination
could have conceived, are absolutely stupefying; and, as
an elementary knowledge of the subject is almost a necessity
even for those who do not dabble in science, I may, after
giving a few notions about light in general, expose very
succinctly the most important points of this procedure,
which is enriching astronomy each day with new and bril-
liant conquests.
Few sciences give rise to so many surprises as that of
light, in regard to which two very different hypotheses have
s been formed—that of emission, to which the name of
Newton long lent great authority, and that of undulations,
started by Descartes, and now very generally adopted.
The hypothesis of emission supposes a luminous body to
propel in different directions a material substance of extreme
tenuity, so subtle as to render it impossible to ascertain its
weight and solidity; a substance which, passing through
certain bodies without any loss of velocity, may yet be
brought to a stop by others. When this substance comes
in contact with an organ of the vision, part of it makes its
way into the interior of the eye, and produces the sensation
of sight.
In the hypothesis of undulations, instead of supposing the
transport of a material agent to great distances, it is held
that the vibrations of luminous bodies are communicated to
the atoms of an all-pervading ethereal fluid. These vibra-
tions, propagated through this fluid, reach the organ of
vision, which in turn transmits them to the optic nerve. In
this hypothesis, the nature and the transmission of light
would be analogous to the nature and transmission of sound,
light being produced by atomic, and sound by molecular
vibrations.42
ASTRONOMY.
The most recent experiments of the savants—the re-
searches upon interferences,’amongst others—have led to a
general acceptance of this latter hypothesis.
II.
' It is known that light declines or diminishes in force or
intensity in proportion as it recedes from the point whence
it emanated. This diminution is in direct ratio to the
square of the distance; for instance, if the distances are
1,	2, 3, 4, &c., the quantities of light received at distances
2,	3, 4, &c., will be 4, 9, 16 times, &c., less than at
distance 1.
Boemer, the Danish astronomer, by an observation of the
eclipses of Jupiter, succeeded in ascertaining the speed of
light. He noticed that it always took 16 minutes and
36 seconds longer to reach the Earth when Jupiter was in
conjunction with the Sun, upon the other side of the
ecliptic, than when that planet was upon our side in oppo-
sition to the Sun. Hence he concluded that light must
take that time to traverse the whole diameter of the
terrestrial orbit, that is to say, about 182,000,000 miles,
and that consequently it must be 8 minutes 13 seconds
in coming from the Sun.
Until the experiments of M. Fizeau it was never supposed
that the speed of light could be arrived at by terrestrial
observations; but by an extremely simple procedure he
proved that the luminous movement travelled 11 \ miles in
the -Tffrs- of a second. This figure is almost the same as
4hat arrived at in antecedent observations, but a slight want
j jf clearness in the impressions obtained prevents this mea-
' surement from being so precise as those taken in the
heavens.LIGHT,
43
M. Foucault tried a new mode of measurement, in 1862,
by means of a revolving mirror, and ascertained that light
had a velocity of 186,250 miles a second. The procedure
alluded to above gives 192,500 miles, so that there is a
marked difference in the results.
- Many objections have been taken to this latter method.
The light had only traversed a space of 37, feet, and in
this short distance it had undergone five reflections and
pierced an object-glass, which, it was suggested, might
have occasioned a diminution- of velocity. It was urged
also that no one can tell what is’ the totality of phenomena
<which take place in a reflection, and that in fact the result
of the experiment did not or might not apply to light in an
open space. Nor can one place unlimited reliance upon the
extreme micrometrical divisions which it was necessary to
make use of.
M. Cornu made some further experiments for the purpose
of ascertaining the exact rate at which -light travels, the
results of which he has recently laid, before the French
Academy of Sciences.
His mode of observation is in the main similar to that
adopted by M. Fizeau, except that he has perfected certain
details, and amongst them may be pointed out a, means of
registering by electricity the speed of the notched wheel,
which it is all the more necessary to ascertain, for this
wheel is used for making a direct comparison as to the
velocity of light. His own point of observation was an attic
in the Polytechnic School, and the other point a. room in
the barracks on Mont Val&ien. In this way M. Cornu
lias obtained sufficient data concerning the velocity of light
to enable him to decide between the rate of 192,500 or
193,750 miles, as given in former calculations, and that of44
ASTRONOMY.
186,250 miles, as established by M. Foucault in his experi-
ments with the revolving mirror.
To quote his own words:—“ My observations concord
with those of M. Foucault, though it is necessary to point
out that his experiments required verification, both because
their details and the mode of procedure, not having been
made public, had not been subjected to discussion, and
because the method of the revolving mirror is open to grave
objections, into the nature of which I cannot enter at present.
M. Fizeau’s method is, on the other hand, free from these
objections. Astronomers, again, will find in this new
valuation of the velocity of light a strong confirmation as
to the parallax of the Sun 8".86, which is obtained by com-
bining this number with the constant of aberration. This
was ascertained by M. le Verrier, after three series of
observations relative to the movement of the planets,
especially of Mars and Venus. So we see that in astronomy
it is impossible to overestimate the importance of deter-
mining precisely the velocity of light.” *
III.
When objects are looked at through a glass prism, not
only do they appear to have been considerably displaced by
the deviation of the luminous streaks which pierce the
prism, but also to be covered with bands of the brightest
colours.
If a prism be so arranged that a luminous streak shall
fall obliquely upon one of its facets, and, as it emerges, be
caught upon a screen or a picture, the result will be an
* Paper read at the Acadimie des Sciences, Feb. 10, 1873.LIGHT.
45
oblong figure of a thousand variegated colours, which has
received the name of solar spectrum.*
The law of reflection and refraction, and the various ways
of magnifying objects by means of the lens, were known
before Newton’s time, but the nature of light and the origin
of colours were still a mystery. Without questioning the
fact of their being produced in this way, no one had sus-
pected that a ray of white light was composed of a large
number of single rays, each of itself capable of imparting a
colour of its own. Delille expresses this idea in the lines:
“ Dans les mains d’un enfant, un globe de savon
D&s longtemps prec&La le prisme de Newton,
Et longtemps, sans monter a sa source premiere,
Un enfant dans ses jeux dissequa la lumiere.
Newton seul l’apeivut, tant le progres de l’art
Est le fruit de letude et souvent du hasard.”
There are seven shades especially noticeable in solar
light as decomposed by the prism, which have on this
account been termed the principal orders. Taking them in
their natural order, they are: red, orange, yellow, green, blue,
iruligo, and violet.
In explanation of these phenomena, white light is looked
upon as*composed of an infinity of rays, differing in colour,
and more or less susceptible of refraction, which separate
from each other as they pass through the prism.
The first point noticed in solar radiation is the light
which we receive, and the heat which accompanies it; but
there is also a third and very important order of phenomena,
viz., chemical action. Its influences are not a thing apart,
but the varying effects of one single cause, consisting simply
* See same author’s Histoirt d&t MUeores, fig. 4, p. 7&ASTRONOMY.
46
of a series of undulations which only differ from each other
in regard to their length and the rapidity with which they
are produced;
The tvayes, whose length is comprised between 768 and
,3691million fractions of a millimetre (*03987 of an inch),
Vhave the power of making our optic nerve vibrate, and thus
.produce the sensation ,of light. The diversity ofcolours.de-
pends only upon fthe length of the waves, the longest being
red, and gradually toning off to violet. With the colours ex-
tending from the green to the violet, the luminous waves also
have the power of separating the molecular groups, and pro-LIGHT.
47
ducing chemical effects. These luminous waves extend far
beyond the visible spectrum into a region whither the eye
cannot penetrate, but they can be recognised by the agency
of photogenical preparations. From the green to the red
the waves become longer, and possess the property of
agitating the molecular groups by a purely physical action,
but, in most cases, without decomposing them. . These
waves also extend beyond the red, and thus form a second
part of the spectrum, which is invisible.*
"We know that sound is’produced by molecular, and light
by atomic vibrations, and that the general laws relating to
these different kinds*of vibrations are the same; but it is
- worthy of, remark that the sound vibrations extend much
further than those of light, since the latter, sensible to the
eye, do not embrace more than what is known in acoustics
as an octave•
IV. ' •
Light always travels in; a straight line, through a region
which is perfectly and uniformly diaphanous.But a mere
difference of density is sufficient to bring about its deviation
. from the straight line, and to break it up into heterogeneous
quantities.
As the various strata of the air all vary in density, it
follows that the light of the stars does not come to us in a
straight line, and that we do not see them in the position
which they actually occupy. At the horizpn there are at
least 33' of refraction, or, in other words, rather .more than
the largest diameter of the Sun or the Moon/ Thus,
when the lower margins of the latter luminaries seem to
* Father Secclii on The Sun, Part II#48/
ASTRONOMY.
be just upon the horizon, in reality the whole of their disc
is submerged beneath it (see fig. 12). The same illusions
take place in our observations of the stars arid of far distant
)
Fig. 12.—Phenomena of refraction.
bodies. But as light, in its passage through the various
strata of the atmosphere, does not encounter any sudden
change of density, so it does not break suddenly off, as, for
instance, in its passage from the air into water or a tumbler.
It follows a curved line, and not a broken one. The refrac-
tion of the light from the Sun and Moon gives us the benefit
of their presence for a longer period, as it anticipates theLIGHT,
■19
Fig, 13, —Ike Moon, as seen upon the horizon, appearing flattened by the refraction of its light.50
ASTftONOMY.
hour of their rising! and delays that of their setting. It is
to refraction that we owe the dawn which heralds the
brightness of day, and the twilight which precedes the
darkness of night. The refraction of light also flattens
these luminaries, and makes their disc look oval. This is
all the more pronounced the nearer they are to the horizon,
and, as Biot has remarked, “ when seen from eminences near
the sea-shore it sometimes equals a fifth of the apparent
diameter of the Sun. The Moon’s disc presents the same
phenomenon.”
Light which, having passed through a very refracting
region, reaches a space where the refraction is not so great*
will sometimes stop at the point which separates the two
spaces, undergo a total reflexion, and travel back through
the space which it had already traversed. This peculiar
phenomenon takes place whenever the rays reach the surface
of emersion at too great an angle of obliquity. The fact of
this total reflexion explains all the varieties of magical
phenomena known as mirages.
In my work on the “ History of Meteors/1 a chapter is
specially devoted to this subject, and contains many facts ^
connected therewith which I ascertained during my travels
in the New World.
V.
The phenomena of luminous interferences will appear
to people who are not well acquainted with optic discoveries,
perhaps even more marvellous and incredible than those of
the mirage.
Supposing a bright ray of solar light to come in direct
encounter with a sheet of white paper, for instance, itLIGHT.
51
follows that the portion of the paper on which the ray
strikes will he made to shimmer. But what seems incredible
is, that this portion may he made quite dark without
touching the paper, without arresting or diminishing the
luminous ray, but, on the contrary, by increasing it.
The magic mode of changing light into shade, day into
night, is even more remarkable for its simplicity than for
its prodigious effects, consisting, as it does, in conducting
on to the paper, by a slightly different trajectory, a second
.luminous ray, which of itself would have made the paper
still more brilliant. One might imagine that the two rays,
when they met, would have this effect; but, on the contrary,
light added to light produces darkness! The movements
of these rays neutralise each other, and the light ceases to
cast any lustre. It will happen, however, that these lumi-
nous rays, by reason of their direction, only partially
neutralise each other, in which case there is merely a dimi-
nution of the lustre.
These are the curious phenomena, which, obliterating or
diminishing light by the adjunction of a luminous ray, have
received the name of interferences.
Of the thousand rays of variegated shade and refrangibility
which compose colourless (or white) light, those only are
capable of neutralising each other which possess co-ordinate
colours and Refrangibility. Thus, a red ray cannot be made
to obliterate a green ray.
If, again, two white rays cross each other at a given
point, it may happen that, in the infinite series of various
coloured lights of which they are composed, the red ray, for
instance, will alone disappear, and that the point of their
intersection will become green—green being white minus the
red.53
ASTRONOMY.
Two rays which have been changed from the -state of
natural light into polarised rays following the same direc-
tion, will still possess the property of interference, com-
bining or neutralising each other like, and under the same
conditions as, ordinary rays.
Two rays which pass, without any intermediate stage,
from their natural state into that of rays polarised at right
angles, are definitely deprived of the property of interference.
Though their course, the character, and the thickness of
the spaces they traverse be modified in a thousand ways;
though they he brought back to the state of reflections com-
bined of the requisite properties, or to parallel polarisations,
it will be impossible to make them obliterate each other.
But if two rays which were polarised in two rectangular
directions, and which could not, therefore, have any influence
upon each other, had in the first place undergone parallel
polarisations when transformed from their natural condition,
they could be made to obliterate each other merely by
restoring them to the state of polarisation with which they
were originally endowed.
It is impossible to avoid a feeling of surprise when one -
learns, for the first time, that two luminous rays are capable
of destroying each other, and that darkness may result from
the conjunction of two lights; but it is still more extraor-
dinary that this property can be given and theft taken away
from them, in some cases momentarily, in others altogether.
The theory of interferences, looked at from this point of
view, might seem rather the product of a diseased brain,
to use Arago’s expression, than the strict and inevitable
outcome of numerous experiments which cannot be con-
troverted.
It was in this theory that Fresnel found the key to allLIGHT.
53
the beautiful phenomena of colouration engendered by the
crystallised plates, or films, which are endowed with double
refraction, proving that they were special instances of
interference. Dr. S. Young has achieved his greatest renown
by his experimental and complete demonstrations con-
cerning interferences, and the principles which he laid down
were set forth and still further applied by Fresnel.
The theory of undulation suggested by Descartes in
explanation of the phenomena of light, had been already
accepted by the savants, and the most recent experiments
in regard to interference confirm its perfect accuracy.
Those who would reconcile the Bible with modem science
will gather, from what I have stated as to the nature of
light, that Moses may have said with truth that light was
created before the celestial luminaries, inasmuch as it is
but a manifestation of undulations*
VI.
We now come to the question of the spectrum analysis.
It is not only the sunlight which can be decomposed and
made to produce a spectrum, but any other kind of light as
weii. It is, however, very remarkable that these lights,
when decomposed, give different spectra, and by examining
their character that of the bodies which produce them can
also be ascertained.
The study of a body by the analysis of its spectrum is
termed the spectrum analysis.
M. Delaunay, of the Institute, gives the following resumS
of this discovery, so fruitful in its consequences. In order
to separate, if possible, the partial images produced by the
various unmixed lights, of which uncoloured (or white)54
ASTRONOMY.
light is composed, one naturally endeavours to make each
of these images as narrow as possible, to prevent them from
encroaching upon each other. This may be done by ad-
mitting the light from without through an opening in the
shape of a narrow chink, standing some distance back to
examine it, and placing the prism in such a way that its
square edges will be parallel to the length of the chink.
Wollaston tried this plan in 1802, a century after Newton
had discovered the solar spectrum; and the result partially
answered his expectations. Submitting certain artificial
lights, such as the flame of a candle and an electric spark,
he obtained results analogous to, but not identical with,
that yielded by the sunlight. Yet Wollaston, in thus looking
with the naked eye through the prism, obtained but a vague
glimpse of the phenomenon which he was in research of,
and which Fraunhofer was destined to discover in all its
splendour.
In 1815 that noted Munich optician, without being aware
of the essay made by Wollaston thirteen years previously,
endeavoured to scan through a prism the spectral outline of
a ray of light admitted through a narrow chink; and to
observe it more closely he made use of a glass. The
spectrum then appeared to him traversed, not by four or five
dark rays, as it did to Wollaston, but by a far greater
number. He saw, in fact, as many as five or six hundred.
He then proceeded to measure accurately the relative posi-
tions of a large number of these rays, and made a drawing
of the spectrum, with 854 of them in their respective places.
He also ascertained, like Wollaston, that the spectra given
by artificial lights are distinguished by a special disposition
of these rays, and, in some cases, even by a complete
absence of them.LIGHT.
55
Fraunhofer’s discovery drew the attention of scientific
men to the subject, and numerous experiments were under-
taken for the purpose of studying the curious phenomena
which he had revealed to the world.
It must be added, that a very remarkable relation has been
established between the brilliant rays produced by gas in a
state of combustion, and the obscure rays which this same
gas creates in the spectrum of a light passing through it.
These rays, brilliant in the one case, obscure in the other,
occupy absolutely identical places in the spectrum. Where
hydrogen gas, for instance, produces a brilliant ray when on
fire, the same gas produces an obscure ray by the absorption
which it exercises upon an extraneous light passing through
it. This remarkable circumstance, known as the inversion
of the spectrum, was first pointed out by Foucault, in 1849,
and definitely established by Kirchhoff * ten years later.
Such are the various phases which the question of spectrum
analysis has passed through.
YII.
Thus we find that every substance in a state of ignition
yields its special spectrum, and without seeing the body which
is burning, we can, by a mere examination of its spectrum,
tell to a certainty how it is composed.
Gold, when incandescent, emits a spectrum different from
that of silver, and that of silver differs again from other
metals, &c.
The main properties of some metals are so alike that it is
almost impossible not to confound one with the other in
the ordinary mode of investigation, and metallurgists have
* Delaunay’s Notice sur VAnalyse Spectrale.ASTRONOMY.
E>6
consequently resorted to an examination of their spectra
when incandescent. By means of spectral comparison and
analysis they have discovered differences not to be traced in
the substances themselves, and by this procedure have
already discovered three new metals: rubidium, ccesium, and
thallium.
Spectrum analysis also leads us to an important chemical
discovery, which M. Dumas laid before the French Academy
of Sciences in 1871. M. Lecoq de Boisbaudran had, some
years ago, demonstrated the affinity between spectra of
alkaline metals and those of metals coming out of an
alkaline soil. He had shown that the displacement of
characteristic rays was effected in accordance with the same
law as the modifications in the weight of the elementary
substances. Messrs. Toost and Hautefeuille, on the one
hand, and M. Ditte on the other, having followed up these re-
searches, ascertained that the course of the rays towards the
ultra-violet hue manifests itself exactly in the same way as
the increase of the atomic weights does for carbon, silica,
titanium, tin, and zirconium upon the one hand, and for
sulphur, selenium, and tellurium on the other. M. Dumas
pointed out that this is but another proof, amongst the many
which science already possessed, as to the truth of the prin-
ciple upon which, in 1827, he established his classification
of simple bodies into natural categories.
Spectrum analysis may also be very useful in physiology
and medicine. In some cases of poisoning,, the toxical
element can be ascertained by burning a part of the flesh or
excrement, and by decomposing through the prism the light
produced by the combustion. It was in this way that M.
Lany discovered thallium in the organs of animals to which
that substance had been administered.LIGHT.
57
But it is in astronomy that its results have been most
remarkable. This science has made use of the spectrum
analysis to extend its researches over milliards of millions
of leagues, and by its means has ascertained the character
and elements of the countless luminaries which pervade
space.
Here is an instance: a brilliant star having suddenly
made its appearance (May, 1866) in the constellation of the
Corona Borealis, and almost as suddenly vanished, its light
was at once submitted to spectrum analysis, and it was proved
that this star was one already known as emitting a very dim
light, which had momentarily brightened. Its spectrum had
great analogy with that of our sun, and we are told by
Messrs. Huggins and Miller that “the spectrum of this star,
coupled with the sudden outburst of its light, and its almost
equally rapid diminution in intensity, make it probable that
owing to some vast internal convulsion, enormous quantities
of gas were emitted from it, the hydrogen in which must
have taken fire by its mixture with some other element, and
caused the light represented by the brilliant rays, the flames
raising the solid matter in the photosphere of the star to a
white heat. The hydrogen burnt out, the light would then
have gradually diminished in brilliancy, and the star would
resume its normal appearance.” It must be borne in mind
that, owing to the immense distance of the star in which
this fire (to use a word which designates the phenomenon
with great accuracy) took place, the light must have taken a
considerable period to reach us, and that it had been at
an end ten, twenty, a hundred years or more, before we were
made acquainted with it.*
* Delaunay’s Notice sur VAnalyse Spedrale.58
ASTRONOMY.
VIII.
Spectrum analysis, by enabling us to read in a ray of
light the nature of the body which produces it, the elements
constituting that body, and the changes that take place in it,
becomes as it were a messenger from the stars, the confidant
of infinite space, the telegraph from incalculable distances,
the revealer of the closest secrets, and even a relentless
denunciator.
Mr. Huggins has published a work upon the spectrum
analysis which contains many new and important facts, and
to it we shall often have occasion to refer.
The various spectra differ from each other in many
important respects, but they may all be divided into three
categories.
1st. The distinctive character of spectra of the first order
consists in the continuity of those coloured bands broken by
no ray, brilliant or obscure. Whence we learn that the light
in which this spectrum has its origin is emitted by an opaque
body, which probably exists in a solid or liquid state. A
spectrum of this order does not disclose to us the chemical
nature of the incandescent body whence the light proceeds.
2nd. The spectra of the second order are formed from
coloured rays of light isolated from each other. They
indicate to us that the brilliant matter emitted by the light
is in a gaseous state; and as each element and each compo-
nent body, which has become luminous without being
decomposed, is distinguishable when in a gaseous state by
certain rays peculiar to it, it follows that these rays are
capable of revealing to us the nature of the bodies from
which they are emitted.
3rd. The third order comprises the spectra of incan-LIGHT.
59
descent bodies, solid or liquid, in which the continuity of
the coloured bands is broken by sombre rays. These latter
are not produced by the source of light, but by vapours
through which the light has passed on its way. Spectra
of this kind are yielded by the light of the Sun and of the
stars. The group of sombre rays produced by each vapour
is identical, as regards their number and their place in the
spectrum, with the group of brilliant rays of which the light
is composed when the vapour has become luminous.
IX.
As the Moon and the planets have no light of their own,
and only shine with the reflected light of the Sun, their
spectrum must consequently resemble that of the Sun,
modified only by the passage of the light through the atmo-
spheres of the planets or by the reflexion on their surface.
The spectrum of the Moon does not indicate that our
satellite is surrounded by any atmosphere, nor any other
distinctive feature. In that of Jupiter there is a dark band
corresponding to certain atmospheric terrestrial rays, and
indicating therefore the presence of vapours similar to those
in our own atmosphere. Another band denotes the pre-
sence of certain gases and vapours which do not exist there.
The spectrum of Saturn is somewhat faint, but it contains
certain rays similar to those in the spectrum of Jupiter.
M. Janssen ascertained that many of the atmospheric
rays are produced by vapour of water, and it is probable
that this aqueous vapour does exist in the atmospheres of
Jupiter and Saturn. He goes on to say:—“During my
recent mission to Italy and Greece, I took observations of
several planets in regard to this point, notably from theGO
ASTRONOMY.
summit of Etna, where the influence of the atmosphere is
almost nullified. These observations, and some subsequent
ones, made with the most powerful instruments, indicate the
presence of vapour of water in the atmospheres of Mars and
Saturn, thus adding a new and important feature to the
already close analogies which connect the planets of our
system. So we see that all these planets form as it were
one family, circulating around one focus, which distributes
amongst them heat and light. Each of them has its year,
its seasons, its atmosphere, and many of them are known to
contain clouds within their atmosphere.
“ And, in addition, water, which is so important an
element in the economy of every organism, is also comfnon
to them. These facts give us strong ground for supposing
that life is not the exclusive privilege of our little Earth,
herself but one of the younger sisters in the great family of
planets! ” *
Certain rose-tinted groups have been remarked in the
spectrum of Mars, which may have some connection with
the red hue distinctive of this planet.
The spectrum of Venus does not show any additional ray
to denote the presence of an atmosphere. The absence of
these rays may perhaps arise from the fact that the light is
probably reflected, not by the surface of the planet, but by
clouds some height above it.
X.
The stars, though much farther from us than the Moon
and the planets, possessing, as they do, their own source of
* Memoir read to tile Academic des Sciences.LIGHT.
61
light, furnish us with more detailed information as to the
nature of the elements of which they are constituted.
Until the secret of spectrum analysis was discovered, we
knew nothing about the stars, beyond the fact of their im-
measurable distance, and their striking beauty; now, we are
in a position to learn some details of their real character.
Spectrum observations tell us that the stars resemble the
Sun, as to the general character of their composition.
Their light, like that of the Sun, emanates from a matter
raised to an intense white heat, and traverses an atmosphere
of absorbing vapours. Yet, notwithstanding this structural
unity, each star differs from the other, though not to an
essential degree, in its chemical composition. Judging
them by their spectra, they may be divided into four per-
fectly distinct types, though a few of the spectra, instead
of belonging to one of these four categories, seem to be
intermediate between them.* With a few exceptions, the
terrestrial elements which are most largely distributed
amongst the stars are precisely those which are essential to
life as it is on the Earth, such as hydrogen, sodium, mag-
nesium, and iron. The hydrogen, sodium, and magnesium
also represent the ocean, which is an essential part of a
world constituted as the Earth is.
Looking at the stars generally, they seem brilliant, like
colourless diamonds, red, orange, or yellow tinted; but
this is not so if they are carefully watched, or observed
through a glass, for then we can see next to the red or
orange-tinted stars others of a blue, green, or purple colour.
The spectrum analysis shows us that these diverse colours
are produced by the vapours in suspense in their atmo-
spheres, and we know that the composition of a stellar
* Father Secchi on The Sun> p. 300.62
ASTRONOMY.
atmosphere is in turn dependent upon the elements which
constitute the star, and upon its temperature.
Spectrum analysis of the variable transient stars also
reveals to us the phenomena produced by the incessant
changes that react upon the rays which these stars trans-
mit to us. Thus it is that we have received tidings of the
great perturbations taking place in the brilliant star Corona,
which was only recently observed, and which has already
decreased in brilliancy.
XI.
During the last 150 years astronomers have been con-
stantly revolving in their minds the veritable nature of the
slightly luminous nebulosities (nebula) which stand out
from the dark surface of the firmament—conglomerations so
filmy in substance as to remind one of the comets. This
question has become all the more interesting now that they
are held to be a part of original matter—embryo stars.
The telescope has failed to enlighten us on this head,
though it is true that since the object glasses have been
made larger, many of these bodies have turned out to be
actual stars. But at the same time other nebulosities,
hitherto undiscovered, have been brought within the field of
vision, to say nothing of other fantastic figures (aggrega-
tions of diffused light), which it is impossible to look upon
as the produce of the combined brilliancy of countless
suns situated at distances more or less unfathomable.
Spectrum analysis has settled this long-vexed question;
has shown us that certain nebulae were not masses of
distinct stars, but matter in a gaseous state, and has even
enabled us to ascertain their elements.LIGHT.
63
' Mr. Huggins, describing his first experiment on this
head, in August, 1864, says:—“ I selected one of the
luminaries in the class of nebulae, which was very small, but
relatively brilliant. Great was my astonishment when, on
looking through the small glass of the spectrum apparatus,
I discovered that its spectrum had no longer the appearance
of a luminous coloured band such as a star would have pro-
duced, and that in place of the continuous band there was
nothing to be seen but three bright rays, isolated from each
other.1”
This spectrum must, so far as it was possible to judge,
have proceeded from a light emitted by matter in a
gaseous state. The most brilliant of its rays was produced
by a body analogous to nitrogen, or, as Mr. Huggins thinks,
even more elementary than nitrogen, and which we have not
as yet been able to analyse. The weakest of its rays corre-
sponded with the green of hydrogen. The mean ray of the
group was almost, but not quite, identical with the ray of
barium.
In addition to these brilliant rays, there was a continuous
spectrum, singularly faint, proceeding from a diffused light,
which seems to correspond with the centre of the nebula.
This is proof that it contains a nucleus, very small, but
more brilliant than the rest of its mass.
Mr. Huggins has since analysed the spectra of more
than sixty nebulae or stellar masses, which maybe divided
into two groups; the first comprising the nebulae, which
give a spectrum such as that just described, or, at all events,
a spectrum comprising one or two of the three rays in
question. Of the sixty which he examined, about a third
belong to the class of gaseous bodies: the light of the
remaining forty produces spectra of apparent continuity.64
ASTRONOMY.
The harmony between the results of spectrosocpic and tele-
scopic observations, in regard to what is common to both,
is a proof of their accuracy; half of the nebulae with a
continuous spectrum have been shown to be stars, and in
process of time another third will probably be added to the
number. But Lord Eosse failed to ascertain this definitely
concerning a single one of the gaseous nebulae*
XII.
Mr. Huggins was the first to apply the spectrum analysis
to the study, not of matter, but of the motion of the stars.
If they possess any motion of relative importance, their
rays must undergo a certain amount of displacement, and
by this means these motions may be estimated. In respect
to some stars, Sirius in particular, his researches have
established the motion of these rays beyond all doubt.
He also applied this effective procedure of analysis to the
observation of the comets, and arrived at the strange con-
clusion that the central part has a light of its own analogous
to the flame of compound carburets, whereas the nebulosity
emits only a light received from the Sun. This delicate
distinction, says M. Faye, is of the highest importance in
studying the physical constitution of these bodies. I may
add that the spectrum experiments conducted by Alexander
Herschel have proved that sodium exists in a state of
luminous vapour in the train of many aerolites.
The result of the spectrum studies goes, therefore, to
prove that the stars only vary from each other, and from
the Sun, in special and minor ways, and that there are no
important and essential differences in their constitution.
M. Faye, in one of his reports to the French Academy ofLIGHT.
65
Sciences, says : “ Thus we see extended to dl the stars of
the universe that unity of composition, which distinguishes
our solar world and the aerolites; unity which is, however,
compatible with many variations as singular as they are
unlooked for.’*
These same results lend a great semblance of truth to the
supposition that the stars have a function analogous to that
of our Sun; and that they are, like it, surrounded by planets
which they keep in place by force of attraction, and which
they illumine and vivify by their light and heat. So it may
well be—and eminent astronomers have given such an
opinion their sanction—that these distant regions are
inhabited by beings intelligent like ourselves, capable of
studying the harmony of creation, and of appreciating the
power of its supreme Author.
Pig. II.—Helios (the Sun). Rhodes Medal in the British Museum.CHAPTER IV.
THE SUN.
Its nature—Light and Aspect presented by its Surface—Grains of Rice,
Willow-leaves, Straw-motes, &c.—Pores, Faculae, and Spots in the Sun—
Formation, nature, and motion of Spots—Rose-coloured Shadows, Red
Protuberances—Change of Shape in the Spots—The Sun obfuscated by
their enormous quantity—Rotation of the Sun—Synodical Revolution
—Sidereal Revolution—Periodicity of the Spots—Solar Electricity and
Hydrogen upon the Earth, and in the Planetary Regions—Solar Explo-
sions—Constitution of the Sun—Two opposite hypotheses—Is the Sun
inhabited ?—Curious Anecdote—Recently acquired notions about the Sun
—Temperature of the Sun—Curious Calculations—Is there any probability
of the Sun ever ceasing to shed light, heat, and life upon the Earth—
Lucretius and our modem Astronomers—Zodiacal Light: its nature—
Some parts of the Sun more brilliant than others—Atmosphere of the Sun
—Various elements of which the Sun is composed—The Seasons—
Dimensions and distance of the Sun—Variation of its Diameter—Its
influence upon the Earth—Recapitulation.
I.
" This star among the stars/’ to use Arago’s expression—
“ the light of the world/* as Copernicus calls it—“ the
heart of the universe/* in the language of Theon of Smyrna
—we see shining like a luminous globe, incessantly darting
in every direction its rays, which transmit with inconceivable
rapidity both light and heat.
Most of the ancient philosophers looked upon it as a
burning body, which lighted the world with the emanation of
its substances. In modem days there prevail two opinions,
which I set forth in the chapter on Light; one being that the
Sun does, as a matter of fact, emit luminous matter emanatingTHE SUN.
67
from its own disc; the other, that space is filled with a
rarefied and elastic substance, which is called ether. This
substance, by the vibratory motions which it transmits with
great rapidity, produces to the eye the phenomenon of light,
much in the same way as the vibrations of the air produce
to the ear that of sound. This latter theory is the one now
universally adopted.
If the Sun’s surface is examined through the powerful
instruments which science has at command, it will be
found to present the irregular and undulating appearance of
a stormy sea, covered with crevices and hillocks, and dotted
over with spots of a more or less dark colour. At times
may be seen, particularly close to the edge of the spots,
luminous masses, known as facula. To obtain a more
complete knowledge of the Sun’s structure, it must be
examined through a powerful ocular glass, at a time when
the atmosphere is perfectly still. Then it will be found
that the surface is covered with a multitude of small grains,
all of about the same dimensions, but varying very much in
shape, though the majority of them are oval. A somewhat
similar result is arrived at by examining through the
microscope milk that has been standing some time, the
globules of which have lost their regularity of shape.
These grains sometimes unite in small groups, when they
present a more brilliant appearance, while their oval shape
has led to their being compared to grains of rice and willow
leaves. The collections of these grains near the solar spots
ore somewhat different, for they seem to be longer, and to
be joined to each other, perpendicularly to the edges of the
penumbra, and look like straw-motes of unequal length, or
the thatch on a roof seen through the telescope; the Sun also
seems to be dotted with spots, of various shapes and size, lessastronomy.
brilliant than the rest of its disc. They are simply solutions
of continuity in the solar photosphere, caused by clouds
composed of metallic vapours.
Fig; 15.—ApjpoanuiQe of the Sun’s surface as seen through powerful glasses.
II.
The solar spots generally look like round black patches,
though it often happens that they are clustered in such a
way as to form an' irregular figure, with the central part,
which is called the nucleiis or umbra, black; the contour,
which is mezzo-tinto, is termed the penumbra, the whitish
spots being known as faculse.THE SOTT.'
69
These spots were at one time supposed to be satellites
revolving round the Sun, and, subsequently, to be clouds
floating in its atmosphere, and even masses of scoriae floating
Fig. 16.— Front view of a spot on the Sun.
upon the sea of fire which constitutes its surface; or even
mountains whose beetling flanks may have produced the
phenomenon of the penumbra.
It is now about a century since Wilson (England) proved
to demonstration that the spots were due to cavities of which
he had been able to ascertain the precise depth; and he at
the sanie time gave an exact idea as to the composition of
the photosphere-—that is to say, the luminous stratum which
envelops the Sun.
The dimensions of the spots vary very much, some being
mere black spots known as yores, others having a surface
much larger than that of the Earth, some few being four
or five times larger than the surface of our globe. The70
ASTRONOMY.
spots are not equally distributed all over the disc. There
are not many in the immediate vicinity of the equator,
and next to none in the latitudes exceeding 85 or 40
Fig. 17.—Spot observed close to the edge of the Sun.
degrees, but they are much more abundant in the two
symmetrical zones comprised between 10 and 30 degrees of
latitude.
Their number is also very variable; sometimes there are
so many of them that in a single observation one can
ascertain the zones which usually contain them. In 1637
they were so numerous that the heat and brilliancy of the
Sun were perceptibly diminished, and history records many
similar obfuscations brought about by the same cause. At
other times they are so rare that a whole year passes away
without one of them being seen. The phenomena which
they present seem at times to have only a superficial
influence, but, generally speaking, it extends to the depth
of the solar body, which is often agitated and heaved up
over a wide expanse, amounting occasionally to a quarter
of the whole disc. Thus it is possible that these spots
may be the outcome of a violent agitation amongst theTHE SUN.
71
matter of which the Sun is composed. The most plausible
hypothesis' is that attributing them to the influence of
the planets (of Jupiter, Venus, and Mercury, in par-
ticular), the attraction of which create regular tides on the
.solar globe and the great disturbances already men-
tioned.
III.
Father Secchi, whose opinions, the result of most careful
observation, are shared by many astronomers, looks upon
them merely as solutions of continuity in the stratum of
mists , or luminous vapours which; form the photosphere.
These clouds differ from ours in two respects, being com-
posed not of vapour of water, but of the vapour of metallic
substances, and, by reason of their elevated temperature,
they are luminous of themselves, but are less brilliant than
photosphere. So far as the external aspect goes, it is the
completely identical; .the Earth covered with clouds, would
appear mammiform in structure like the Sun to any one
placed at some distance from it, and the phenomenon has
even been remarked from mountain summits, especially
during a thunderstorm.
This theory, as Father Secchi points out, explains, with-
out having recourse to fabulous rates of speed, the rapidity
with which certain changes in the shape of the spots take
place. The apparent displacement of a cloud may be under-
stood without supposing that the substance has traversed
the same space as the contour of the cloud, for it may
be accounted for by> a change of temperature, producing
upon the one hand condensation, upon the other, dissolu-
tion of the vapour over a considerable surface. He puts.72
ASTRONOMY.
the question as to the nature of the spots in this way—“Are
they caused by an obscure substance, rising above the
luminous substance, or is it not rather the luminous matter
which penetrates into an obscure region
He goes on to point out that all the phenomena alluded
to are only to be explained by the second hypothesis: that
there exists in the spots a luminous substance which pene-
trates into a less brilliant region—call the clouds an obscure
part if you will, but it is none the less true that the
luminous part penetrates thither. The spots must contain
a transparent substance, less brilliant than the photosphere,
and of a gaseous character. Our atmosphere .would appear
the same to a spectator looking into it from outside, say
from the Moon; the clouds lighted up by the Sun would
seem brilliant, while he would see black spots at the points
where the air was transparent.*	,
M. Faye, of the French Institute, has, on the other hand,
propounded the hypothesis that the spots are whirlwinds
caused by the unequal speed of the successive zones of the
photosphere, the angular rotation of which diminishes in
speed from the equator to the poles, and that their law of
motion denotes at the same time their distribution over the
solar surface. In a report read to the Academic des Sciences
(Dec. 80th, 1872) he says that this is naturally the case,
because these spots are neither more nor less than whirl-
winds engendered directly in the photosphere by the unequal
speed of its parallels. In another memoir, he indicates a
very curious similitude between solar and terrestrial cyclones,
the laws of these two orders of phenomena seeming almost
identical.
In reality, Father Secchi’s theory is not incompatible
* Father Secchi on The Sun, p. 77.THE SUN,
73
with that of M. Faye, for the former, in reply to the argu-
ments quoted above, says—“ The question as to whether
the spots are whirlwinds is but of secondary importance,
for, even admitting them to be so, the only cause by which
they could be originated would be an eruption.”*
IV.
The spots often change in shape and vanish after having
appeared for a short time, or traverse the whole visible
surface of the Sun, following a line oblique to the diurnal
motion and the plane of the ecliptic, and reappearing in
their original condition at the expiration of twelve or
thirteen days.
The motion of these spots has revealed to us the remark-
able phenomenon of the Sun’s rotation upon itself.
Jordan Bruno, of Naples, author of a “ Treatise upon
* Father Secchi’s Memoir to the Academic des Sciences, March 3, 1873.74
ASTRONOMY,
the Universe,” published in 1591, was the first to suspect
this fact, which was definitely ascertained to be correct by
Jean Fabricius, from whose memoir, published in 1611, I
quote the following passage:—“ I conceived the idea of
attracting the Sun’s rays through a very small aperture to a
darkened chamber on to a sheet of white paper, I noticed
that this spot (one which Fabricius had discovered in the Sun)
had taken the shape of an elongated cloud. After an
interruption of three days, caused by the bad weather, my
observations showed me that the spot had made an oblique
movement westward. I also noticed a smaller one close to
the edge of the Sun, which in a few days reached its centre,
and after that a third. The first of the three soon dis-
appeared, and the others at an interval of two or three days.
" I was apprehensive that they might not return, but at
the end of ten days the first one reappeared in the east.
It then became clear to me that these spots were
accomplishing a revolution, and my opinion was confirmed
by other persons to whom I pointed them out. I hesitated
for some time to publish my observations, the accuracy of
which seemed affected by the fact that these spots did not
maintain the same distances from one another, and that
they underwent a change of shape and speed. It was, there-
fore, all the more gratifying for me to remember that, as the
spots are apparently on the actual body of the Sun, which
is spherical and solid, they must necessarily diminish in
size and slacken their speed as they reach its edges.” *
From a close observation of the spots it has been con-
cluded that the Sun revolves upon itself in a periodof about
twenty-five days, and like the Earth from east to west.
Schemer puts the synodical, that is to sajT, the apparent
* Fabricius, translated by Lalande.THE SUN.
75
revolution, in which the spot seems to an observer to return
to the same point upon the disc, at twenty-seven days.
This gives twenty-five days and a third for the duration of
the sidereal revolution—that is to say, the time taken by a
given point of the Sun to describe a complete circle. Thus,
in place of observing the rotatory motion of the solar
body itself, we are compelled to study that of its atmo-
sphere, being, in fact, similarly placed to an astronomer who,
to ascertain the rotatory motion of the Earth, had taken up
his position in the Moon, with a cloud as his point of com-
parison. He would first of all have to study the atmospheric
circulation and discover the laws by which it was governed
—a task so difficult under such circumstances, as to be well-
nigh impossible.*
V,
Schwabe has compiled a long series of statistics concerning
the periodicity of the solar spots, having from 1826 to 1868
observed the Sun every day that the state of weather per-
mitted. The result of his observations was that he recog-
nised the existence of a positive periodicity, very marked
maxima and minima succeeding each other at an interval
of about ten years. This decennial period coincides very
unexpectedly with several meteorological phenomena on the
earth,—amongst others, as recent observations testify, with
the variations of magnetic force and the periodicity of aurorae
boreales.
The periodicity of the spots indicates, as Father Secchi
remarks, a periodicity in the solar activity, and the variations
of this activity may well be communicated to the Earth,
Father Secchi on The Sun, p. 111.70
ASTRONOMY,
either by means of heat or some other channel as yet
unknown, such, for instance, as electro-dynamic induction,
thus producing upon our globe meteorological or electric
phenomena.*
The theory expounded by M. Becquerel at the Academie
des Sciences, in 1871, is in confirmation of this view. He
maintains that all the causes which elicit electricity from
the Earth’s surface would be insufficient to supply the
enormous quantities which are diffused in the planetary
regions, and even in our atmosphere. He goes on to show
that the hitherto unknown origin of this electricity can be
none other than the Sun. The spots upon this luminary,
some of them 40,000 miles in extent, seem to be the
cavities from which the hydrogen and the various substances
composing the solar atmosphere are emitted. Now, hydrogen
conveys with it the positive electricity which becomes diffused
in the planetary regions, permeating thence to the terrestrial
atmosphere, and even to the earth itself. The matter which
electricity carries with it suffices for its transmission, it
having been proved that electricity has the property of
becoming diffused in a void space if it has any accompanying
matter. The phenomena of the polar aurora produced by
electric discharge also prove, in M. Becquerel’s opinion, the
existence of gaseous matter in space, far beyond the bounds
assigned to the terrestrial atmosphere, it being certain that
these aurorae are at least 125 miles distant from the earth’s
surface.
M. Charles Sainte-Claire Deville points out that the facts
adduced by M. Becquerel in support of the celestial origin
of atmospheric electricity confirm his own hypothesis as to
the celestial origin of the variations of atmospheric tempera-
* Father Secchi on The Sun, p. 33C.THE SUN.
77 '
ture> and, especially, as to the influence which the periodical
apparition of cosmical substances in the interplanetary
regions may have upon these phenomena.
The following facts will fit in harmoniously at this point.
Signor Tacchini wrote from Palermo to the Acaddmie des
Sciences, that the aurora borealis of February 4th, 1872,
was a phenomenon so extraordinary as to have few parallels
in scientific annals, and that its apparition was accompanied
by corresponding movements upon the surface of the Sun.
The bad weather prevented Signor Tacchini from taking
spectrum observations on the 3rd and 4th of February, but
lie noticed, on the morning of the 5th, that the whole
Fig. 19.—Motions noticed upon the Sun’s surface by Signor Tacchini,
during the aurora borealis of February 4th, 1872.
surface of the Sun was in an abnormal condition. The rim
was covered with bright flames; towards the north pole they
exceeded 20 seconds, with an arc of 86' to right and to left,
corresponding with a bright region of magnesium which, at
the western rim, extended almost to the equator. In this
portion, at 50 degrees from the pole, was seen a magnificent
prominence, which rose to 2' 40'', and from this point, at
an arc of 40 degrees, the rim was lighted with brilliant
flames, while the atmosphere was studded with small lumi-
nous filaments, or bright specks, about 2 minutes in height.78
ASTRONOMY.
Signor Tacchini also sent a drawing to illustrate these
phenomena (see fig. 19).
M. Cheux, communicating to the Academie des Sciences
the features of a white aurora borealis observed near Angers,
on the 8th of August, 1872, states that the Sun had been
for some time in a very effervescent state, and that on
examining it with a Foucault telescope on the 9th of August,
he saw about 24 spots, one of which, a deep black, was very
beautiful. The drawing which accompanied his description
is reproduced in fig. 22, p. 88.
Senor Capello, of Lisbon, also sent some drawings of the
Sun as it appeared on the 8th, 9th, 10th, and 11th of August,
after the same aurora borealis (see figs. 23-26, p. 94).
Father Sanna-Solaro, in a memoir on the same subject,
argued that if the Sun is taken to be the principal source of
atmospheric electricity, the facts, otherwise most difficult to
co-ordinate, immediately link themselves into the chain of
phenomena, conveying with them, so to speak, their own
explanation. Father Sanna-Solaro is, in my opinion, one
of the highest authorities on meteorological subjects, and
his work upon the “ Causes and Laws of the Movements in
the Atmosphere ” may be studied with profit.
VI.
At the same time, there is anything but an unanimity of
opinion as to whether the Sun is the main cause of the elec-
tricity by which we are surrounded. M. Faye, in a very able
treatise in support of his own theory, says: “ We know that
there is a fundamental difference between electricity and
heat or light. The greater the vacuum the more rapid is
the propagation of light and heat, so much so that certainTHE SUN.
79
specialists, supposing a material medium to be necessary,
propounded the idea of filling the infinity of space with
absolutely' imponderable ether. But electricity requires
ponderable matter in order to manifest itself in the shape of
currents or of simple force, attractive or repulsive. Electric
experiments carried on in a place where there is an approach
to a void, are very feeble in their results, and they come to
a full stop in a laboratory where a complete void has been
created. Thus, I repeat, the electric agencies in question
must be conducted in a ponderable space. Now, we have
seen that if the celestial regions are furrowed in all directions
by numberless corpuscles, shooting stars, aerolites, remains
of comets, and even, perhaps, by solar hydrogen, etc., these
small masses of ponderable matter, accomplishing their
distinct orbits round the Sun, could not possibly form a
continuous mean like the air in which we set electricity into
action.
“I should not have thought it necessary to insist upon
this idea, but that my colleague, M. Becquerel, had recently
brought it into prominence by his endeavour to connect the
Sun with our own atmospheric electricity. M. Becquerel
admits that the solar mass is incessantly emitting hydrogen
which becomes diffused in space, conveying with it its own
electricity, essentially positive, and communicating it to the
stars on its passage, without, however, coming in contact
with their atmospheres. I do not intend to discuss these
ideas, merely wishing to point out that the hydrogenous
emanations of the Sun would not constitute a continuous
mean capable of serving as a vehicle of communication to
electric repulsions or attractions. Repulsed from the Sun by
the supposed electricity of the chromosphere, or rather,
perhaps, by the repulsive force of the photosphere, these80
ASTRONOMY.
molecules would also be endowed with rotatory speed; they
would, therefore, describe hyperbolic curves convex towards
the Sun, and branching towards all parts of the universe.
Thus they would speed along in separate directions, gradually
getting further from each other, without being capable of
exercising the mutual reactions which constitute an electric
mean or a gas.”*
M. Becquerel still maintains his theory that the Sun is
the probable origin of electricity, and has answered M. Faye’s
arguments in a treatise laid before the Academie des Sciences,
in November, 1872.
VII.
Before proceeding further, it will be as well to explain
what is meant by the solar atmosphere, and the phenomena to
which it gives rise. This atmosphere is double; the first part,
which envelops the centre of the Sun, is called the photosphere.
Like the region which it surrounds, it is the seat of vast
chemical processes. As it radiates towards the celestial
regions it loses a portion of its heat, while the gaseous
bodies which it contains, becoming cool and condensing into
vapour, relapse into the interior of the Sun, to return afresh
into the photosphere, and recommence the same trans-
formation. Such is the explanation given of the first
atmosphere by those who are of opinion that the Sun has
no solid nucleus—an opinion which is generally accepted in
the present day, and the reasons for and against which will
be found below.
The solar photosphere, according to Father Secchi,t must
* M. Faye, and the Academie des Sciences, Oct. 9th, 1872.
+ Father Sccclii on The Sun, p. 219.THE SUN.
81
contain vapours of every variety, which, owing to their
extreme levity, must attain a great altitude. If a large
number of bodies, looked upon by mineralogists as elementary7
—precious metals in particular—have not been discovered
in the Sun, it does not follow that there are none, for it
may well he that these metals, owing to the great density
of their vapours, are detained in profound regions inacces-
sible to spectrum analysis. The following is the nomen-
clature given to substances known to exist in the Sun,
arranging them in the order of their atomic weight, from
the lighter to the heavier:—hydrogen, sodium, magnesium,
aluminium, silicon, ‘potassium, calcium, chromium, manganese,
iron, copper, zinc, and barium.
Beyond this luminous envelope or photosphere, which
forms the apparent limit of the solar disc, is an atmosphere
properly so called, transparent, hut endowed with a sufficient
power of absorption to arrest a part of the solar rays. It
is not of uniform altitude, attaining the maximum of height
at the equator and near the spots, and the minimum at the
poles.
This atmosphere, which completely envelops the Sun, is
almost entirely composed of hydrogen of a veiy high
temperature; it also contains a small quantity of sodium
and magnesium vapour, and even of vapour of water. In it
may be noticed aggregations of rose-hued patches, analogous
to the flames which may be seen round the moon’s disc
during the solar eclipses, and which are known as red
protuberances. Hydrogen is the main element of these
phenomena.
G82
ASTRONOMY.
VIII.
Father Secehi points out that, by virtue of the law of
superficies, the inner strata of the sun must have a rotatory
motion more rapid than the outer ones, and that the friction
has not perhaps set up a motion of identical character
throughout the whole mass. The points situated at the
equator must be vested with a speed greater than those
nearer to the poles, as is proved by the motion of the spots.
He admits, at the same time, that the exact theory of
circulation in the solar mass is not yet completely solved,
and that we must for the present put up with hypotheses on
the subject.
It also results from his observations, that the length of
the solar diameter is to be decided by the amount of activity
of the sun itself, and that the diameter of the disc is least
where the activity is greatest. This unlooked-for conclusion
concords with the general comparisons that have been made
between the length of the diameters and the number of the
protuberances.*
The Sun is the seat of explosions which seem to be
connected with the production of spots. Father Secchi
has even succeeded in obtaining some definite information
as to one of these phenomena, the results of which he laid
before the Academic des Sciences (August 5th, 1872),
accompanied by the drawing reproduced in figs. 20 and 21.
This phenomenon occurred at 3.30 p.m. on the 7th of
July, 1872. At 2.40 p.m. there was nothing but a small
luminous jet; the internal motions of the incandescent
vapours were so intense that the luminous clouds were seen
to change in shape in a moment; and at 4,15 p.m. they had
* Academic dcs Sciences, Sept. 9tli, 1S72.THE SUN.
8 3
reached an altitude ten times greater than the diameter of
the Earth, or, in other words, of 79,000 miles. This
Fig. 20.—Solar explosions.
eruption lasted two hours, and was repeated the next day
at the same point in the Sun. Father Secchi adds, that at
the same date an Aurora Borealis was seen at Madrid- and
many other places in Europe, and the phenomenon was
also accompanied by violent magnetic perturbations in
many places.
The zodiacal light also extended over an unusually
wide space, whence he concludes that these various
phenomena are connected with each other* and that the
great motions of the solar photosphere have their counter-
part upon the earth. An examination of figs. 20 and 21
will show that the large cumulus-shaped cloud (a), which at
3.50 p.m. was just above the jets, was formed by theASTRONOMY.
entanglement and fusion of the jets themselves, and that
when the mass had risen and spread itself out, the cloud
Fig. 21.—Solar explosions.
seemed to break up into filaments, curved in shape like the
acanthus leaves of a Corinthian pillar (figs, b, c, d, e).
At the same time, the curves of these jets are not only
parabolic, but actually spiral, for the volute is seen to be
forming at the extremities of the filaments. This fact, first
pointed out by Young, has been confirmed beyond the pos- .
sibility of a doubt during the eruption of July 18th (see
fig. 21).
Fig. a represents the aspect of the strange phenomenon
at 8.50 p.m., on the 7th of July; fig. b at 4.15; fig. c at
4.80; fig. d at 5.10; fig. f at 6.80. Fig. f represents the
last traces of the eruption of the 7th, suspended in the air
above some faint flames. Fig. a represents the eruption of
July 18th, at 11.85 a.m.; fig. h at 4.85 p.m.; and fig. i at
6.20 p.m, Fig. k represents a spot displaying traces of the
eruption observed upon the 11th of July near ,the Sun’s edge.
IX.
The question as to how the Sun is constituted was con-
sidered by the most distinguished of astronomers longTHE SUN.
85
before the discovery of the spectrum analysis enabled the
enquirer, seated in his study, to ascertain what was taking
place millions and milliards of miles away, and the result
naturally was that many diverse theories were propounded,
Herschel, Laplace, and several other astronomers of mark,
held that the Sun consisted of an obscure body, surrounded
by an atmosphere in which floated a deep stratum of clouds,
and only the upper part of which was in ignition; whence
it would follow that the Sun might be inhabited. This
ingenious theory takes account of the various appearances
presented by the spots with which the solar body is often
studded, and acquires great probability from the polarizing
experiments made by Arago. It has, however, been called
in question of late years, chiefly owing to the results
obtained from the spectrum analysis. If a flame containing
metallic vapours is submitted to this analysis, their presence
is denoted by characteristic coloured rays; but if behind
this flame is a second luminous source more intense than
the first, and containing the same metallic vapours, instead
of the superposed rays receiving an accretion of brilliancy,
the rays of the fainter focus will absorb those emanating
from the more ardent one, and in the place of luminous
there will be obscure rays. And, as the solar rays emit
precisely similar beams, and give what is technically termed
an inverse or reversed spectrum, Kirchoff has concluded that
the body of the Sun must be more incandescent than its
atmosphere.
But M. Petit, a former director of the Toulouse
Observatory, in a memoir communicated to the Academie
des Sciences, points out that this theory takes no account
either of the spots, penumbne, faculse or luculse, or of
the absence of polarization. And as the total eclipses of86
ASTRONOMY.
the Sun have recently revealed that the photosphere is
surrounded by a second aeriform envelope, luminous like
the first, though in a minor degree, he very justly says that
the inverse spectrum of the sun is easily to be explained, if
we suppose that the second atmosphere contains metallic
vapours of the same nature as those in the first. He
concludes, therefore, that it is not necessary to admit that
the solar nucleus is in a state of fusion, and Herschers
opinion as to the possibility of the Sun being inhabited
need not be called in question. He adds, “ Instead of an
incandescent body, which must in the nature of things
become cool and die out, we might thus imagine an incessant
revivifying of the combustible properties, by organised
beings inhabiting the surface of the solar nucleus, and
maintaining the equilibrium, just as the plants and animals
do in our own atmosphere.”
Arago says, “ If I were asked the simple question—‘ Is
the Sun inhabited?’ I should reply that I did not know.
But if I were asked whether the Sun is habitable for beings
organised like ourselves, I should have no hesitation in
answering in the affirmative. The existence in the Sun of
an obscure central nucleus, .enveloped in an opaque atmo-
sphere, separated by a considerable space from a luminous
atmosphere, is by no means inconsistent with such a
supposition. Herschel believed that the Sun was inhabited.
He maintained that if the solar atmosphere, in which the
luminous chemical reaction takes place, is a million leagues
deep, there is no reason why the brilliancy should anywhere
exceed that of an ordinary Aurora Borealis. The arguments
upon which he relied as proof that the solar nucleus is not
necessarily very hot, notwithstanding the incandescence of
the atmosphere, are neither the only nor the most powerfulTHE SUN.
87
ones that might be adduced. The direct observation, taken
by Father Secchi, as to the lessened temperature of those
points on the solar disc where the spots are noticed, is, in
regard to this fact, of more importance than all the theoretical
arguments put together. Dr. Elliott asserted, as early as
1787, that the sunlight was given by what he called a dense
and universal Aurora Borealis, and he held, with the
ancient philosophers, that the Sun might be inhabited.
When he was tried at the Old Bailey for the murder of
Miss Boydell, his friends—Dr. Simon amongst others—
declared that he was out of his mind, and cited as a clear
proof of his insanity the pages in which the opinions just
quoted were embodied. The ideas of a madman are nearly
always adopted. This anecdote seems fitted to figure in
the annals of science, and I have taken it from * Brewster’s
Encyclopaedia.* ”*
X.
The astronomers of the present day are less unanimous
than they were in Arago’s time as to the possibility of the
Sun being inhabited; butM. Vicaire, in a communication to
the Academie des Sciences, endeavours to show that we
must go back to the theory of Wilson, Herschel, and Arago,
as to the existence, within the photosphere, of a nucleus
comparatively cool and obscure.
To use his own language : “ The principal objection that
has been advanced against the hypothesis is that this
nucleus, subject to the radiation of the photosphere, would
long since have acquired the same temperature. This
Arago’s Astronomic Populaire.88
ASTKONOMY.
objection falls to the ground if the . heat received by this
nucleus is' employed in vaporizing the liquid of which it is
formed. Moreover, this heat may and must be only a
trifling fraction of what is emitted by the photosphere,
absorbed as it is by the intermediate stratum, which is
incessantly re-conducting it into the photosphere. As to
the length of time that the nucleus has been subject to this
volatilization, there is nothing to prove that it is to be
measured by the total duration of the earth. I believe, on
the contrary, that the sun, as at present constituted, has
only shone upon this globe since the most recent geological
periods..”*
Many astronomers, Father Secchi and M. Faye among
them, believe that the whole mass of the Sun is gaseous,
Fig. 22.—Surface of the Sun on the 9th of August, 1872, at 6 a.m., as
observed by M. Cheux.
and that the speed of its various strata increases from the
surface to the centre. The former says: “ When the Sun
* AcacUinic des Sciences, Aug. 26th, 1872.THE SUN.
89
at the epoch of its formation had reached a volume about
equivalent to that which it now possesses, its temperature
would have been at least 500 million degrees, and, moreover,
we know by experiments that even now its surface tem-
perature amounts to several million degrees; that of the
interior is probably higher still. We must conclude from
these facts that the Sun cannot be composed of a solid mass;
nor, enormous as may be the pressure existent in this mass,
it cannot possibly, so to speak, be in a liquid state. Whence
we are necessarily led to the supposition that it is gaseous,
notwithstanding its extreme condensation.”*
M. Delaunay, of the Institute, says: “ The enormous
temperature which the Sun must possess, renders very
probable the existence in its atmosphere of the various
bodies just mentioned (different metals). Upon the other
hand, as the volume of the Sun is 1,260,000 times that of
the terrestrial globe, and as its mass is only 314,760 times
that of the Earth, the mean density of the Sun is only a
quarter that of the Earth, and consequently not much
greater than that of water. Such being the case, it is
difficult to believe that the Sun is a solid body enveloped
in a covering of brilliant clouds, constituting what is termed
the photosphere. I am inclined, rather, to agree with M.
Faye, that the Sun is a gaseous mass with a very elevated
temperature, which prevents the elementary substances
that enter into its composition from consolidating; while
their decrease in heat superficially, brought about by the
radiation into the celestial spaces beyond, would facilitate
the production of combinations, which in turn, owing to the
formation of solid and pulverulent precipitates, disseminated
Father Secchi on The, Sun, p. 289.90
ASTRONOMY.
in the outer strata of the gaseous mass, would produce the
brilliant light of the photosphere. These solid precipitates
would, by reason of their greater density, gradually descend
into the inner portion of the mass, where they would be
decomposed by the high temperature and again become
gaseous. Moreover, these descending currents would cause
the formation of ascending currents, by means of which the
matters in the inner part would be brought to the surface,
so that the whole gaseous mass would in this way contribute
to sustain the vast production of heat and light upon the
Sun’s surface. The spots, varying in number, position,
shape, and size, which are generally visible in the Sun,
would merely be gaps accidentally made, amidst the reful-
gent clouds of the photosphere, by the currents alluded to
above.”*
For my own part, after comparing the various solutions
that have been proposed, I must pronounce for the gaseous
nature of the Sun.
XI.
In a letter to M. Dumas, which was read at the Acaddmie
des Sciences, in the early part of 1869, M. Janssen, whose
researches in connexion with the spectrum analysis have
obtained great notoriety, supports this view by a summary
of the knowledge hitherto acquired as to the constitution of
the Sun. This communication, stated succinctly, shows
that modern research, interpreted by M. Faye’s theory,
tends to the conclusion that the Sun is essentially a gaseous
globe, with a temperature of its own so elevated that no
Delaunay’s Notice sur VAnalyse Spcdralc.THE SUN.
91
substance or body can exist there, save in a very gasiform
state. But it is known that gases, even when raised to a
very high temperature, are but faintly luminous when they
do not contain particles of a fixed body—that is to say, of
one not reduced to gas. How, then, are we to explain the
brilliancy of the Sun ? In this way. The region in which
the solar globe moves causes a diminution of temperature
upon the surface of that luminary, sufficient to condense
within it the gaseous elements and reduce them into solid
dust. This dust, mixed up with the incandescent gases,
gives them the effulgency and radiation which we perceive,
just as carbon, lime, and magnesium impart the luminous
property to the dull flames of our own gases.
Thus, by a relative decline of temperature, the gaseous
globe is surrounded by a very luminous envelope; this is the
photosphere, or visible part of the Sun—the Sun itself as it
appears to the general public. In this photosphere are
visible spots and rents which have attracted the careful
attention of astronomers. These rents in the luminous
envelope, the diameter of which is often double or treble that
of the earth, enable us to ascertain that the central gaseous
nucleus is relatively obscure; their motions have revealed
the law of the superficial rotation of the Sun—a rotation, the
speed of which varies according to the latitudes, and thus
have supplied us with one of the most striking proofs of the
gaseous character of the Sun.
It is the examination of the spots, too, that has led
astronomers to admit the existence of an atmosphere around
the luminous envelope. But the existence of this atmo-
sphere, which has since been revealed by the phenomena of
refraction noticed on the photosphere, and by the effects of
absorption remarked upon the edges of the solar disc,92
ASTRONOMY,
was only guessed at, and its nature, its altitude, and its com-
position were the objects of the most contradictory state-
ments. As to those singular luminous appendages or pro-
tuberances which have been observed during the latest total
eclipses, absolutely nothing was known about them. Such
was the state of things when the great eclipse of August
18th, 1868, supplied the first opportunity for applying the
new method of analysis to these phenomena.
Analysis of the light of these protuberances revealed first
of all their character and their gaseous composition. These
large appendages are almost exclusively composed of in-
candescent hydrogen. It has also been remarked that this
hydrogen exists over the whole circumference of the Sun,
and that the protuberances are but the more prominent parts
of this hydrogenic atmosphere.
When this interesting memoir, here summarized, was
read, M. Leverrier remarked that the theory which consisted
in treating the Sun, in regard to its luminous portion, as
an incandescent globe, covered with a small gaseous atmo-
sphere, to which part of the phenomena observed upon its
surface are attributable, has been established beyond the
possibility of doubt by the observations taken dining the
total eclipse of 1860. The important point ascertained
during the eclipse of 1868 is as to the nature of this
atmosphere; and M. Janssen, by making it possible to
observe, at any period, phenomena which had before been
visible only at the moment of a general eclipse, had rendered
a great service to science. Upon the same occasion,
M. Leverrier read a memoir from M. Eoyet, in which
it is shown that the yellow ray discovered by the spectrum
analysis is visible upon the whole contour of the Sun; whence
he concludes that the incandescent gas to which it corre-THE SUN.
93
sponds is, upon the same principle as hydrogen, a constitutive
element of the solar atmosphere. At the same time, we do
not at present know what this gas is, for the ray in question
does not coincide with the yellow ray of sodium.
XII.
The question naturally arises : Why is the temperature of
the Sun so enormous ? It may have been caused by the
very force of the gravity which conjoined the elements that
formed the central point of the solar system. In the first
instance, the temperature thus mechanically acquired must
have been much higher than it is at present, now that the
Sun is getting cooler. At the same time, the diminution of
its heat, great as it may be, is almost imperceptible to us,
being, as it is, so gradual, and partially compensated by the
transforming of a portion of the solar mass into various
chemical combinations. It may also be that certain foreign
bodies, attracted into the Sun, help to maintain its inces-
sant combustion. There is a great variety of opinion as to
the sum of the solar temperature, and it is very asto-
nishing to find that the researches of the specialists lead
them to such widely different conclusions. During the last
few years much has been written upon this subject, and one
of the most recent treatises is that of M. Vicaire, who points
out that Father Secchi estimates the temperature at
10,000,000 degrees Cent., while M. Spoerer puts it at not
more than 37,000. And if to these opinions I add that of M.
Pouillet, who thinks that it is not less than 1,461, or more than
1,761 degrees, my readers will see that science has not yet
reached any satisfactory conclusion in regard to this matter.
It is even more surprising that the most opposite results,94
ASTRONOMY.
those of Secchi and of Pouillet, have been deduced from the
same phenomenon, viz., the calorific radiation of the Sun,
the intensity of which they estimated by an almost identical
process. As M. Vicaire remarks, so enormous a difference
August 8tli, 7h. 29m. p.m.	August 9th, 7h. 15m. p.m.
August 10tb,' 8h. 5m. p.m.	August 11th, 9h. 42m. p.m.
Figs. 22a. to 25.—Aspects of the Sun during the Aurora Borealis of August, 1872.
in the results evidently cannot he due to the observations,
but to the manner in which they have been interpreted;
and, after careful consideration, he arrives at the conclusion
that Pouillet’s evaluation is far nearer the truth than that
of Father Secchi. Upon this, M. Elie de Beaumont pointed
out how Sir William Thomson had shown that the Sun’sTHE SUN.
95
temperature cannot be so very much higher than that
attained in certain manufacturing processes, and adverted to
his treatise upon solar heat, in which he states that the
quantity emitted, according to Pouillet, is not equal to
more than a seven-thousand horse power to each square
foot of its surface. Coal burnt at the rate of a pound in
two seconds would produce almost the same result, and
Bankine has estimated that in the locomotives coal is con-
sumed at a rate not greater than a pound per square foot in
from thirty to ninety seconds.
This great problem as to the surface temperature of the
Sun is, as M. Elie de Beaumont adds, more accessible now
than it once was. This is principally due to the astrono-
mical expeditions for studying, at the epoch of total eclipses,
the physical constitution of the Sun, not the least important
of which was that of 1858 to Panaragua in Brazil.
The result of M. Becquerel’s researches in regard to the
question of high temperatures, and the phenomena of irra-
diation which accompany them, leads him to the conclusion
that the highest temperatures which can be produced by
combustion or electric agency do not exceed 2000 or 2500
degrees Gent., and that consequently the solar temperature,
which is not so widely removed as might be supposed from the
temperatures of these sources, wrould not exceed 8000
degrees.
M. Fizeau thinks that if the solar radiation is, as a
matter of fact, greater than the most intense sources of
light which the Earth can produce, it has not, nevertheless,
been found more than double or treble that of the light
proceeding from them all. Thus these two sources oi
light are in all points comparable, whence it is to be inferred
that their respective temperatures cannot differ very widely,96
ASTRONOMY.
as certain estimates recently formed about the temperature
of the solar surface would tend to proVe. M. Fizeau’s
argument seems to me very conclusive.
M. H. Sainte-Claire Deville says, that to speak of veiy
elevated temperatures and their measurement is to admit
that the gases are capable of dilation or compression by heat
to an indefinite extent—a fact which is not proved; or else
that there is no limit to the chemical combinations, of
which there is even less evidence. He also points out that
to calculate the temperature of any given point of the Sun’s
mass is to neglect altogether the influence of the stratum—
a very deep one, for all we know—of obscure solar matter
which, so far as we can judge, overspreads the incandescent
stratum, and the radiation of which towards the Earth is
also eliminated. He goes on to notice a fresh experiment
which might help to settle the question. The hydrogen
rays emitted by certain points of the Sun’s incandescent
matter, have been ascertained by astronomical observations;
Frankland and Lockyer found them present in hydrogen
flame subjected to a certain pressure, and it follows that the
combustible temperature of hydrogen at this same pressure
can be calculated, and, as a necessary consequence, the
character and pressure of the gases at those points of tho
solar atmosphere where the hydrogen rays have been noticed.
The result of the first experiments upon this head induce
him to believe that the temperature is somewhere about
2500 or 2800 degrees, which corresponds with the subse-
quent experiments of Bunsen and Debray.THE SUN.
97
XIII.
To complete this summary of the opinions arrived at by
the most eminent astronomers, I will now add the conclu-
sions come to by Father Secchi concerning solar tempera-
ture, its origin, and its sustenance.
1st. The solar temperature is of several million degrees,
though it is impossible to say precisely how many.*
2nd. This temperature is to all appearances the result of
gravity, and must have been produced by the collapse of the
matter which constituted the primitive nebula and which
now composes the Sun and the planets.
3rd. At this epoch of formation the temperature must
have been much higher than it now is: therefore the Sun is
in process of cooling.
4th. Though the Sun is continually losing vast quantities
of heat, the diminution of temperature is almost impercep-
tible, not exceeding one degree in four thousand years.
This is due to the state of disjunction in which the matter
remains under the action of the heat.
5th. Though the temperature of the Sun is not altogether
invariable, its secular variations are, at the same time,
slighter than the frequent fluctuations which we remark
without being able to investigate them completely. There-
fore we may take for granted that our planet will continue
to be habitable for a long series of ages.
He proceeds to say that “ though the temperature of the
Sun is not altogether invariable, yet the variations are so
trifling that they are only perceptible after many thousands
of years. After a still greater lapse of time—after many
millions of centuries, for instance—the Sun will become
much cooler; and a time will, no doubt, arrive when it will
* This estimate is, as mentioned above, very much contested.
H98
ASTRONOMY.
no longer possess the property of sustaining life upon the
surface of the planets. It is possible that the Creator has
thus ordered things from the beginning, with the purpose of
repairing its activity by some extraordinary phenomenon,
such, for instance, as the fall of a nebula. But these are
points upon which it is unnecessary for us to dwell. Who
can say whether the order which now reigns in our solar
system is intended to last indefinitely ? As we know from
geology, the present state of things has not always been
going on, and as it has had a beginning, why should it not
have an end ?” *
XIV.
Lucretius forestalled our modern astronomers when he
said: “ I am aware how novel and incredible an opinion I
express in predicting the future collapse of the Heavens and
the Earth, and how difficult it will be for me to convince
people of its truth. This is always the case when one pro-
pounds a truth to which utterance has not yet been given,
and which, moreover, is not susceptible to the ear or the touch
—the two sole conductors of evidence into the sanctuary of the
human mind. . . . You believe, perhaps, that the Earth and
the Sun, the Heavens and the Sea, the Moon and the Stars
are divine substances, destined to be eternal; that it is,
consequently, an act of impiety, equal to that of the Giants,
and meriting the severest punishment, to dare by vain
arguments to shake the vault of the world, to extinguish
the Sun which shines in the heavens, and to subject im-
mortal beings to destruction. But all these bodies are so
far from having anything in common with the divine nature,
and so unworthy to be placed in the rank of Gods, that they
* Father Secclii on Tlie Sun, p. 292.Tni) stiff.
99
are rather calculated to give us an idea o-f brute and inani-
mate matter; for you must not suppose that feeling and
intelligence are common to all bodies alike.
“ Moreover, if the Heavens and the Earth have never
had an origin, if they subsist since all eternity, how comes it
that there was no poet to celebrate the achievements pre-
ceding the war of Thebes and the downfall of Troy ? How
is it that so many heroic deeds are buried in oblivion and
excluded for ever from the eternal annals of fame ? I am
certain that our world is new; it is yet in its infancy, and
its origin does not dgfte far back. This is why certain arts
are perfected and others only invented to-day; navigation is
but just beginning to progress; the science of harmony is
a discovery of our own time; and, lastly, that philosophy,
the principles of which I expound, is but of recent date, and
I am the first of my countrymen who has been able to
discourse about it.” *
This train of reasoning is not very conclusive, but the
quotation just given expresses in beautiful language the ideas
which were current upon this topic in the days of Lucretius*
To bring the subject of solar heat to a conclusion, I may
add that researches about the Sun date from a very early
period. Lucas Valerius remarked that its image was more
brilliant at the centre than at the edges. This important
fact was called in question by Galileo, but it is correct, as
has been proved by recent observations, those of Father
Secchi amongst others. The latter also show
1st. That all radiations undergo a considerable absorp*
tion> tvhich increases from the centre of the solar disc to
the edge, where it is at its maximum.
2nd. That the equatorial regions are of a higher tempe-
* Lucretius, Book iv.
h a100
ASTRONOMY.
rature than the regions situated beyond the 30th degree of
latitude, the difference being at least 1-16.
3rd. That the temperature is a trifle higher in the
Northern than it is in the Southern hemispheres.
4th. That just as the spots emit less light, so also do
they emit less heat than the other regions.*
XV.
This is the place for a few remarks concerning the zodiacal
light. This light* is a phenomenon which generally accom-
panies sunrise and sunset, about the period of the equinoxes,
that of spring more especially; it is seen in the form of
a cone of whitish light, which is visible in the direction of
the zodiac, being brightest in the regions where the sky is
very limpid. I have observed it, u4?der specially favourable
conditions, upon the Atlantic^mrin the Southern Seas. In
length it sometimes seemkwro^^^e an arc of ninety degrees.
The ancients designawl^t^^^^by the name of trabes
(rafter), The first savants^wim/attempted to give it a
scientific explanation seem to hajve been J. D. Cassini and
Mairan. Cassini supposed the Sun to be enveloped in a
nebulous stratum, in shape like a very flattened and nearly
lenticular spheroid, extending beyond the orbits of Minerva
and Venus to that of the Earth. De Mairan, who had even
taken detailed observations, of this phenomenon, gives a de-
scription of it corresponding to that of Humboldt, and, like
Cassini, he also connects it with the solar atmosphere, higher’
around its equator, on account of its rotation, which would
account for its elongated form, visible only when the points*
of observation are not plunged in this atmosphere.
* Father Secchi on The Sun, p. 133.THE SUN.
101
M. Liais, in the course of his numerous sea-voyages,
devoted special attention to this phenomenon, and he com-
municated the result of his observations to the Academie
des Sciences in 1858. “ I have demonstrated,” he says, “that
one can only account for the zodiacal light by admitting that
it is due to an imponderable substance forming around the
Sun a sort of nebulosity, in which the Earth is completely
plunged. The annular aspect of this nebulosity is caused
by its forming a sort of flattened ellipsoid round the Sun,
that is to say, a thin stratum of matter very slightly inclined
towards the terrestrial orbit, which is entirely contained in
the interior of this stratum. If, therefore, we look in the
direction of the flattening, or, in other words, of the ecliptic,
we remark a greater thickness of matter than exists in
any other direction. Consequently, we receive more light
from the side of the zodiac than we do from other quarters, so
that this zone appears to us more luminous than the other
parts of the sky, without being so in reality. Everybody
must have remarked that when the weather is very clear no
part of the celestial vault is completely sombre. Owing to
the limpidity of the air, the light from the nadir is also
more pronounced at the tropics than in the temperate
regions. This comes from the solar nebula, to the glimmer
of which is conjoined the slight quantity of light transmitted
to us by the stars.
“ The zodiacal light, when a good view can be got of it,
as in the intertropical zone, is the most beautiful of all
phenomena. In colour it is pure white, though, as seen in
Europe, certain observers have thought that they could
discern a reddish tint. This latter has not, however, any
real existence; for if so it would be better seen at the
tropics, as colouration always becomes more marked inTHE SUN.
103
proportion to its intensity. I believe that observers have
in this instance, confounded the zodiacal light with the last
red traces of twilight. At the tropics themselves, in the
months of July and August for that of Capricorn, and in
the months of January and February for that of Cancer, the
zodiacal light is visible in the evening after sunset, perpen-
dicular to the horizon. When night sets fully in, there
rises in the west a white vertical column, the central axis
of which equals and even exceeds in intensity the most
brilliant parts of the milky way. Upon the edges of this
column the light gradually tones off to the faint glimmer oi
the heavens. It differs in this respect from the milky way,
the edges of which at certain points present a striking con-
trast to the surrounding sky, as in the black aperture of the
Southern Cross called the coal-sack
Silbermann deduces from the observations which he has
made that the zodiacal light has close affinity with the
affluence of shooting stars and the apparition of Aurorae
Boreales. In a memoir communicated to the Academie des
Sciences, he says: “Whenever there is an affluence of
shooting stars, there is an Aurora Borealis, either luminous
or else merely cloudy, in the mean latitudes. Numerous
facts make me think that such is also the case with the
zodiacal light, and this recalls to my mind that the zodiacal
light, like the Aurorae, concurs with sudden oscillations of
the barometer, and that it is sometimes also, like the
Aurorae, of a bright red colour. ,	.	. The sudden
changes of intensity, as well as the appearance of undu-
latory motions, were observed by Humboldt. A zodiacal
light, extending from one edge of the horizon to the other,
like that seen by Beguelin, was observed by M. Liais.
* Liais, Espace Celeste, p. 131.104
ASTRONOMY.
Respighi, again, has recently ascertained by spectrum
analysis that the zodiacal light offers the brilliant ray of
nitrogen discovered by Augtrom in the Aurorae Boreales. All
these facts, as well as the coincidence of the zodiacal light
with the affluences of shooting stars and the Aurorae Boreales,
tend to show that this light is in reality a zodiacal Aurora,
corresponding to the tide waye, and not to that of cosmical
matter. It is known, too, that Laplace would not admit
that the zodiacal light might be a wide extension of the
Sun’s atmosphere.*
XVI.
This notice would not be complete without a succinct
summary of the scientific notions concerning the Sun which
have now long been acquired and popularised in elementary
works of education.
The Sun is incessantly darting its rays from all points of
its surface, and there is not an instant during which its
light ceases to permeate every corner of the universe.
From the close of June it undergoes a daily decrease of
elevation, but the heat, nevertheless, continues to increase
during the summer. And this is easy of comprehension,
for we know that a body warmed by the Sun retains its heat
for some time after it has ceased to be exposed to the solar
rays. If a good-sized piece of metal is exposed to the Sun
during a very hot summer day, it will be found to retain a
certain amount of heat an hour after sunset. It therefore
follows that the Earth, which is so much larger, will retain
during the night, and even until the following morning, part
of the heat communicated to it by the Sun on the previous
Academic dcs Sciences, April 8tli, 1872.THE SUN.
105
day. The Sun adds a fresh amount to that already existing,
and so the Earth obtains an increasing balance of heat. In
this way the heat goes on increasing in the bosom of the
Earth, or in the air to which it communicates itself, until
the nights get longer, when our globe gradually loses the
heat which it had contracted during the summer.
The Sun is placed in the centre of our planetary system,
the Earth revolving around it in the space of about 365 days
6 hours. Until the time of Copernicus it was generally
believed that the Earth was motionless, the Sun revolving
around it; but at that period people were ignorant as to the
immense distance of the Sun from us, and of its real size
(1,260,000 times larger than the Earth), so that they did
not see any reason why it should not revolve around our
planet.
How could it be possible for a body so enormous as the
Sun to travel an orbit of 500,000,000 miles in twenty-four
hours ? The stars, immense globes, whose exact size we
are unable to ascertain, would, to speak only of those
that are least remote from us, have to travel 125,000,000
miles per second. And, lastly, how could the radiant globe
of the Sun circulate around a body so small as the Earth
without dragging it from its place, if it were united to it by
invisible ties ? Or, if the Sun were not attached to the
Earth, would it not pursue its course in space, leaving our
planet hopelessly in the rear ?
If two stones tied together are thrown into the air they
will be seen to circulate around a point comprised in
the interval between them, and which is their common
centre of gravity. If one is much heavier than the other,
the centre of gravity will be proportionately nearer to the
former, and may even be situated within it, in which case100
ASTRONOMY.
the small one will seem to circulate by itself around the
larger one, which will only be slightly displaced. Physics
teach us that the centre of gravity of two bodies is to be
ascertained by dividing their mutual distance in inverse
ratio to their weight or volume, and by means of this calcu-
lation we learn that the proportion of the Sun’s mass to
that of the Earth is as 354,936 is to 1. It follows, then,
that the common centre of gravity of these two bodies
is situated at 243 miles from the Sun’s centre. The
latter, therefore, does not move, the Earth revolving
around it in the space of about 365 days, and turning upon
its own axis every twenty-four hours. The first impression
of our eyesight would of course lead us to suppose that the
Sun and the other planets revolve round the Earth, and it
is this illusion which led the ancient astronomers into
error.
The Sun’s distance from the Earth is about 91,430,000
miles; a cannon-ball travelling at the rate of 1,637J miles
an hour, or 39,750 a day, would take 6 years and 110 days
to reach it. The Sun’s diameter is 852,584 miles, or nearly
four times the distance between us and the Moon. Its dis-
tance varies with the different seasons, and this is why the
apparent diameter of the Sun is not always of the same dimen-
sions. This remarkable phenomenon is occasioned by the
translation of the Earth in an elliptic curve which brings us
nearer to the Sun in summer than in winter; whence it is
that the solar disc seems larger to us in the former than
in the latter season.
Now if we compare the Sun with other bodies which
* people the immensity of space, we are taught by science
' that it is but an insignificant star amongst the countless
legion of luminaries which shine before our eyes. ThisTHE SUN,
107
Fig. 27.—Proportional size of tlie Sun as seen.from the different planets.
From Neptune.
From Mercury.	,, Uranus.
,, Saturn.
,, Venus.	, Jupiter.
„ Hygeia.
,5 the Earth.	%	,, Flora.
„ Mars.10S
ASTRONOMY.
subject will be treated at greater length in the chapter on
the stars.
XVII.
Not only is the Sun the centre around which the planets
describe their orbits ; it is also their centre of life. Nothing
can breathe or live without the beneficent influence of its
ra3rs. Lavoisier gave expression to this idea when he said,
“ Organism, feeling, spontaneous motion, and life, only exist
upon the surface of the Earth and in regions exposed to the
light. One might fancy that the fable of Prometheus was the
expression of a philosophic truth which had not escaped the
notice of our forefathers. Without light, nature was lifeless,
dead, and inanimate. A beneficent Being, in providing the
Earth's surface with light, endowed it with organism, feeling,
and thought.”
In my work upon the “ Laws of Life,”* I dwelt at length
upon the physiological influence of the agents of nature, a
subject to which I can only allude casually in these pages.
Speaking generally, it may be said that the life of every
creature is more perfect in proportion to the amount of light
which it can command, and it even seems that life is not
possible without its influence, for we meet with nothing but
inorganic bodies in the entrails of the Earth, or in the deep
caverns to which it cannot penetrate. In them is no breath-
ing or sentient thing; at most they contain certain kinds of
mosses or lichens, which form the first and most imperfect
phase of vegetation, and on minuter examination it is seen
that most of these plants (if indeed they are plants) only
grow upon or close to rotten timber. And even upon the
* Lcs Lois de la Vie, et VArt de prolonger ses Jours, a work crowned by the
fv ench Academy (Firmiii-Didot & Co.).THE SUN.
109
Earth’s surface, if a vegetable or animal substance is de-
prived of daylight, it will successively lose its colour and
vigour, then stop growing and become stunted, no matter
how carefully it may be nurtured and tended.
Man himself, when deprived of light, becomes pale,
enervated, decrepit, and eventually loses his energy, as
is unhappily too clearly proved in the case of persons who
have been confined for a long period in a dungeon, of
miners, ship’s stokers, workmen in badly-lighted factories,
and the inhabitants of cellars or narrow streets. Heat,
which, it may be, is only light in another form, is not less
needful for life; it alone can develop the first germs of
being. Heat begets life and life begets heat, an indissoluble
bond connecting these two phenomena. It would, in fact,
be difficult to say which of the two is cause and which effect;
all we know is that wherever there is life, there also is, more
or less, heat.
M. Radau, in an excellent work upon the subject, says
that “ the influence which the Sun exercises upon vegetation
is greater than was formerly supposed to be the case. Not
only does it supply the heat which hatches the germs de-
posited in the ground; it also fosters the respiration of the
plants, and, in a certain degree, their growth. And as our
alimentary and combustible substances proceed directly or
by successive transformations from the vegetable kingdom,
it may be said that they represent an amount of active
power borrowed from the Sun in the shape of luminous
\ vibrations, when the elements of which the plants are formed
are in the act of grouping and combining together. The
forces stored up by this gradual process of chemical affinities
reappear, partially at least, in the mechanical efforts which
the animal being is constantly making, and in the shape of110
ASTRONOMY.
which he expends a part of his own substance. They also
reappear in the working of machines fed with coal. They
are transformed into heat when wood is burned in a fire-
place, or a nutritive substance burnt in the blood of a living
thing which has the faculty of respiration, but not of motion.
Thus it is that light, by making the plants to grow and
flourish, prepares their nourishment for the inhabitants of
the Earth, and provides them with an inexhaustible source
of mechanical power.”*
When winter has plunged nature into apparent death, the
mild temperature of spring is sufficient to reawaken its
deadened forces. Beneath its gentle influences the days
lengthen, the Sun’s rays strike us more vertically, and as
their brilliancy increases the fields become bright with flowers,
and the birds gladden the woods with their song. Gradually
the sun reaches its greatest elevation, and begins to decline
throughout the autumn, until winter is once more upon us.
The nearer we approach the poles, the nearer do we seem
to the empire of death, and there are regions where no plant
or insect can live, and which are only inhabited by whales,
bears, and other animals capable of engendering heat, and
preserving a sufficient store of it to protect them against
the rigours of the climate.
XVIII.
I will conclude this chapter by ah extract from Father1
Secchi's work on “ The Sun,” in which he summarizes the
facts hitherto ascertained concerning the great orb of day.
“ That igneous globe, a source of life, and cause of motion
amongst the planets, was once a nebulous mass like those
Radau’s jVerniers Progrts de la Science, p. 46.THE SUN.
Ill
which we now see in the depths of the sky. This mass as
it grew cool gave birth to the planets and their satellites.
It still preserves in its midst all the heat which must have
resulted from its condensation and the collapse of its
different particles, which, from the furthest limits of its
domain, have, in obedience to the law of attraction, fallen
towards the centre.
" This enormous mass, undergoing the phases of gradual
cooling through which the planets around it have passed,
may one day lose the whole of its present brilliancy, but it
will yet be millions upon millions of years before this takes
place. Whether something will then occur to restore its
primitive powers, we cannot say, for the world’s existence
has had a beginning, and may, for all we know to the con-
trary, have an end.
“ The gaseous composition of the Sun accounts for the
phenomena which we notice upon its surface. The part
which is exposed on the outside to radiation towards the
regions beyond loses its gaseous constitution as it gets cool;
it remains condensed in the shape of masses, vaporous but
incandescent, in the gaseous and transparent atmosphere
by which the globe is surrounded, forming a brilliant stratum
which we call the photosphere. This stratum, like the
interior of the solar body itself, is the seat of vast chemical
processes and physical movements of a very complicated
character. Causes as yet unknown, transporting considerable
masses from the interior to the exterior, create immense
gaps in the luminous stratum, and so give rise to the spots.
The centre of these gaps, more obscure and more absorbent,
cuts off from us the great majority of the luminous rays
emanating from the central nucleus, composed as they are
of a gaseous matter and quite isolated from each other.112
ASTRONOMY.
“Above this luminous stratum spreads the atmosphere,
formed of transparent vapours, which attain various degrees
of altitude according to their specific weight. Hydrogen,
being the least dense of all these substances, floats at a
great altitude, forming columns and clouds which constitute
the red prominences seen about the Sun during an eclipse.
Iron and calcium are the substances most abundant in the
hollow of the spots and in the rents of the photosphere.
“ The Sun’s atmosphere is vast, extending to a distance
equal to the fourth of the solar radius; it is elliptic in shape,
with a greater elevation at the equator than at the poles.
In the equatorial regions, in the vicinity of the spots more
especially, there is a higher degree of activity than at the
poles, as .is seen by the greater brilliancy and altitude of the
atmospheric envelope itself.
“ The spectroscope, in revealing to us the chemical com-
position of the Sun, has taught us that the substances of
which it is formed are identical with those which constitute
the terrestrial bodies. And yet we are far from possessing
a knowledge as to the nature of all these substances.”
The information contained in this chapter shows the
progress made in the researches as to the Sun, and the
rapidity with which they have been prosecuted since the
discovery of spectrum analysis.
Fig, 28.—Horse (the Seasons) from a medal of the time of Commodua,CHAPTER V.
MERCURY.
Its phases—Truncation of its Crescent-Prodigious height of its mountains—,
Mercury’s passage across the Sun—Its volcanoes—Its distance from the
Sun—Its seasons—Its density, mass, dimensions, and motions—Strange
peculiarities of this planet—Is it inhabited ?—Fontenelle’s opinion.
I.
Mercury is the smallest of the principal planets and the
one nearest to the Sun. It is always so immersed in the
rays of the latter that there is great difficulty in seeing it
with the naked eye, even at the period when it is most
distant from the Sun.
Yet the Greeks, struck by the occasional intensity of its
light, bestowed upon it the adjective, glittering.	Seen
through the telescope, Mercury has phases like the Moon,
a fact which proves its opaqueness; it is also because of this
latter quality that it presents the shape of a black spot in
its passage across the solar disc. Its crescent exhibits a
horny truncation, discovered by Schroeter, which tends to
show that this planet has mountains 53,000 feet high, or
even more.
Mercury’s passages across the Sun take place but rarely,
because of the inclination of the orbit, occurring at intervals
of three, seven, ten years, &c., and lasting less than three
hours. The luminous points noticed upon its obscure disc
zIU
ASTRONOMY.
on these occasions have led to the supposition that it must
contain volcanos in a state of activity.
The mean distance of Mercury from the Sun is 35,393,000
miles, whence it follows that the Sun’s diameter, seen
from Mercury, appears thrice as large as it does to us,
and that the temperature is seven times that of our torrid
zone. This temperature, much greater than that of boiling
water, is no doubt mitigated by an extensive atmosphere.
Its seasons are very pronounced, for at the epoch of the
solstices, for instance, the Sun attains an altitude, as
compared to the polar horizons, not merely of 23° 27", as
upon the Earth, but of 70 degrees.MERCURY.
115
II.
This planet must be of a very dense character, for if the
materials of which it is composed were liable to become
heated like those of the Earth, they would be melted and
vitrified in a very short space of time.
We know, in fact, from experiments made, that its density
is one and a half times greater than the mean density of the
Earth; its mass is only a twelfth that of the Earth; its
volume sixteen, and its weight fifty-seven times less than that
of our planet.
It traverses, in the space of 88 days an orbit of 230,208,000
miles round the Sun, or 100,000 miles an hour. It was
because of this enormous velocity that the Greeks called
this planet Mercury, the messenger of the gods.
It accomplishes in 24 hours 5 minutes and 28 seconds
a rotatory movement around an axis 7 degrees inclined to
the plane of the equator, so that there must be a great
inequality in the days and seasons. In diameter it is about
2,962 miles, and at its least distant point, 47*229,000
miles from the Earth.
It is a peculiarity of this planet that at its perigee, that
is to say the point when it is nearest to the Earth, it seems
smaller than at its apogee, the point when it is farthest off,
and the reason of this is that when in its perigee it is not
luminous on the side towards us, while when at its apogee
that portion of its disc lighted by the Sun faces the Earth.
It is somewhat strange that Copernicus, who deduced from
the motion of Mercury so powerful an argument against
the Ptolomsean system, lamented upon his death-bed that,
in spite of all his efforts, he had never been able to see this116
ASTRONOMY.
planet. Yet its existence was known in the most remote ages,
and the ancients, who did not comprehend the real system o
the world, deceived by the double apparition of Mercury,
sometimes after sunset, sometimes before sunrise, supposed
at first that there were two distinct stars, one of which they
called Apollo, god of the day and of light, the other, Mercury,
god of thieves. The Indians and Egyptians, who worshipped
this planet, also gave it two different names. But it was
ultimately remarked that only one was visible at a time, and
that the apparition of the second coincided almost exactly
with the disappearance of the first; so it was discovered that
they were one and the same star.
III.
If Mercury is inhabited, it must be by people constituted
very differently from ourselves. Much allowance must be
made for the imaginative powers of painters and poets, and
with this reserve Fontenelle’s description of its supposed
inhabitants is worth quoting.
He says : “ They are not half so far off from the Sun as
we are; it seems to them nine times as large, and floods
them with a light so potent that the brightest of terrestrial
days would appear but dim twilight to them, if not night
itself. The heat to which they are accustomed is so great
that the climate even of central Africa would freeze them
through. It must be taken for granted that our iron, silver,
and gold, would melt in their worjd, and only appear as a
liquid, like water. The dwellers in Mercury would be unable
to comprehend that in another world these same liquids,
which perhaps form their rivers, are the hardest substances
with which its inhabitants are acquainted. They must beMERCURY.
117
so vivacious as to be mad in our meaning of the term. I
believe that they have no more memory than most negroes,
that they have not the faculty of thought, that they only
act by fits and starts, and that in Mercury, Bedlam is the
universe.”
This portrait of the supposed inhabitants of Mercury is
the reverse of flattering, and there is no reason why the
harmony which would be likely to subsist between their
organism and climate should not admit of their intellectual
and moral faculties being developed as perfectly as our own,
if not more so.CHAPTER VI.
VENUS.
Different names of tliis planet—Its distance from the Sun—Its translator
motion—Why does it seem to vary in size ?—Dull and pale light occa-
sionally emitted by its obscure part—Visible in full daylight—Curious
facts: iEneas in his voyage to Italy, and General Bonaparte at the
Luxemburg—Discovery of the phases of Venus—Curious anagram—
Spots observed in Venus—Its gigantic mountains—Explanation of its
phases—Its passage across the Sun’s disc—Its atmosphere—Why does it
seem to remain longer to the east and west of the Sun than it takes time
to revolve around it ?—Means of ascertaining the Earth’s distance from
the Sun by the passage of Venus—Halley, Le Gentil, Chappe—Curious
facts—Its rotatory motion around an axis—Its days and seasons —
Description of this planet and its possible inhabitants.
L
Venus is the only planet spoken of by Homer, who de-
signates it by an epithet signifying beauty. It has also been
called Juno and Isis.
The identity of the brilliant stars seen, sometimes of a
morning and sometimes of an evening, was not originally
known, and thus the ancients called it Vesper, or the evening
star, when it set some time after the Sun; Lucifer, or the
morning star, when it preceded the sunrise.
Venus was called Sukra, that is to say, the brilliant, by
the Indians, and everyone is aware that it is often termed
the Shepherd’s star.
Micrometrical measurement shows that the apparent
diameter of Venus is comprised between 9" *5 and 62".VENUS.
119
This enormous difference is due to the fact that it comes
within 23,309,000 miles of our globe, and recedes to as
much as 159,551,000 miles from it.
It is about 66,131,000 miles distant from the Sun, round
which it accomplishes, in 224 days, 14 hours, 49 minutes,
an orbit of 432,000,000 miles, travelling, therefore, at the
rate of 80,000 miles an hour or 1333 a minute.
So far as we can judge, Venus has a smaller diameter, and
consequently a lesser volume than the Earth, but the differ-
ence is so slight that the observations from which it has been
deduced may not be altogether trustworthy. The quantity
of light and heat which Venus receives from the Sun is
nearly double that which reaches the Earth.
The obscure part of this planet is occasionally noticed to
shed in the sky a dull, deadened kind of light, which some
astronomers have attributed to the phosphorescence of the
atmosphere or the solid part of this planet. This curious
phenomenon may also be the result of a certain ash*coloured
light, analogous to that of the Moon, and which would be
caused by the light reflected from the Earth or Mercury to
Venus. Perhaps, too, the atmosphere of the planet may be
in certain cases the seat of lights analogous to those which,
on the Earth, constitute Aurora Boreales*
II.
Venus is sometimes so resplendent as to be visible at
mid-day to the naked eye, and the uninformed masses have
linked its appearance with important contemporary events,
just as has been the case with comets.
The ancients remarked that at night when there was no
moon, the light of Venus often projected shadows. -Eneas,120
ASTRONOMY.
as we are told by Varro, during his voyage from Troy to
Italy saw this planet the whole time, even while the Sun was
above the horizon. The same author, in one of his works
that is now not extant, is reported by St. Augustine to have
said that Venus had, at an epoch long before his own time,
undergone a change of colour and intensity.
General Bonaparte, on his way to a fete at the Luxemburg
Palace, was struck by the attitude of a crowd in the Hue de
Tournon, which had assembled to gaze at a star, which was
visible, though it was then mid-day. This planet, which was
Venus, they took to be the guiding star of the celebrated
general, who had just returned from his Italian campaign.
It is a singular fact that it was not until some time after
its discovery that Galileo thought of observing whether
or not Venus had phases, a point which he settled in the
affirmative on the 10th of September, 1610.
In order to follow up and verify this discovery without
running the risk of having it appropriated by others, he
concealed it under the following anagram:—
Hcec immatura a vie jam frustra Ugimtur. o, y.
Changing the order of letters, Galileo read the line
thus:—
Cythice figuras emulalur mater amorum.
Father Castelli asked Galileo, in November, 1610,
whether Venus and Mars did not both present phases, to
which the astronomer of Florence, who at first gave an
equivocal answer, replied a month later by announcing the
discovery of phases in Venus.VENUS.
121
III.
The dark spots noticeable in Venus extend over a large
part of its diameter; their extremities are not very sharply
defined.
Branchini noticed, in 1726, seven spots in the centre' of
Venus, which he termed seas communicating with one
another by means of straits, and exhibiting eight distinct
promontories. He drew illustrations of them, and named
them after his patron, the King of Portugal, and the most
distinguished navigators. In 1700, La Hire, observing
Venus by daylight near its lower conjunction, with a mag-
nifying glass of 90 degrees, noticed upon the inside of the
crescent an unevenness of surface which could only be due
to the presence of mountains higher than those of the
moon.
Schrceter, directing his attention to that part of the
crescent nearest its horns, noticed that they were occasion-
ally truncated.
Upon the 28th of December, 1789, January 80th, 1790,
and February 27th, 1793, he remarked near the southern
horn a luminous point entirely isolated, that is to say, sepa-
rated by an obscure patch from the rest of the crescent.
If the planet were free from rugosities and perfectly
smooth, the crescent would invariably terminate in two ex-
tremities quite parallel and very pointed; but if Venus is
covered with mountains, their interception of the luminous
rays proceeding from the sun will at times prevent one or
even both of these horns from assuming their regular shape,
and the crescent will not therefore be completely sym-
metrical.m
ASTRONOMY.
As a matter of fact, Venus is not a smooth body; it
lias mountains upon its surface, and these mountains far
exceed in height those of the earth. From measurements
taken it seems that they are 145,200 feet high, or five times
the altitude of the highest mountains upon the earth.
Fig. 30.—Tlie phases of Venus.
When Venus sinks of a morning into the Sun’s rays, or
when, of an evening, it emerges from them, its diameter is
very small, and its disc nearly round.
This diameter is much larger, and the planet seems very
concave, like the moon under similar circumstances, when it
disappears of an evening, or emerges of a morning from out
of the twilight-dawn.VENUS.
123
The concavity of its crescent faces to the east of an even-
ing, and to the west of a morning. It is half full at the
rig. 31,—The passage of Venus across the Sun,124
ASTRONOMY.
periods intermediate between those mentioned, phenomena
which admit of a very simple explanation, if we suppose that
Venus circulates in a closed curve, with the Sun inside,
that it is not luminous of itself, and that the greater part of
the light which we see there is borrowed from the Sun.
As Venus is situated beyond the Sun in the same latitude,
and crosses the meridian at noon, it is then said to be in
upper conjunction; the bwer conjunction also occurs at noon,
at the epoch when Venus and the Sun have the same
latitude, the former occupying a position between the latter
and the earth.
Venus passes across the Sun’s disc in the direction of left
to right, like a "black spot with an apparent diameter of 59
seconds. Its passages are of very rare occurrence; the first
that was made the subject of observation took place in
November, 1631; the next on June 5th, 1761, and the third
on June 3rd, 1769. After occurring at an interval of eight
years, there was a lapse of one hundred and thirteen and a
half years before the next, which takes place upon the 8th of
December, 1874, and will be followed as before, by another
passage in 1882. This is the order of their periodicity, the
cause of which is the inclination of Venus to the ecliptic. It is
worthy of notice that its passages across the solar disc serve to
ascertain the Sun’s parallax, and its distance from the earth.
Fig. 81 represents the passage of Venus across the Sun,
observed from three different points, A, B, C. At the
moment of its passage it is about two and a half times
nearer to us than the Sun is. Its parallax is therefore very
considerable. Let us suppose two observers, A and B, to
be placed at the extremities of a terrestrial diameter, and
making allowance for the rotatory motion of the earth, each
of them will be able to measure the chord described by theVENUS.
115
planet, either directly, or by estimating the time occupied in
its passage, for the angular motion being well known, the
time taken will show what space has been traversed. The
length of two chords starting from a b being known, their
distance a b will easily be ascertained, and, by means of two
triangles with bases A b B and A a B, it will be found that
the distance of the chords is equal to five times the radius of
the earth. Therefore the angle at which the distance a b is
seen from the earth is five times greater than the angle at
which the terrestrial radius would be seen from the Sun, or
five times the solar parallax. Thus, by taking the fifth of
the distance, a b9 we obtain the parallax of Venus.
IV.
Halley, the 'great English astronomer, was the first to
indicate the passage of Venus as a means of obtaining the
parallax of the Sun or its distance from the earth. Though
Halley must have known that his method could not be
employed in his own lifetime, he nevertheless strongly
recommended it, thinking more of the service he could
render humanity than of lamenting that the brevity of
human life would prevent him from reaping the benefits of
his discovery.”*
The importance of the passage of Venus across the Sun
from a scientific point of view has been the cause of many
perilous expeditions. As the author just quoted remarks:
Imitating the heroic devotion to duty displayed by Halley,
astronomers scoured the whole globe to observe the pas-
sages of this planet. One of them, Le Gentil de la Galai-
• Treatise on Astronomy, y Petit, ex-director of the Toulouse Observatory
vol. ii. p. 137.126
ASTRONOMY.
siere, starting from India in March, 1760, and hindered by
the war then going on between the French and English, had
the patience to await at Pondicherry for eight long years
the passage of 1769, risking the loss of his post at the
Paris Academic des Sciences, where, in default of news
from him, his vacant place was filled up. Thus he risked his
patrimony, and failed after all in the object of his research,
for after obtaining but a cursory glimpse of the passage of
1761, from the deck of a ship, he was altogether prevented
from observing that of 1769, owing to the cloudy state of
the sky.”
The Abbe Chappe d’Auteroche, after making the journey
to Siberia, in order to observe the passage of Venus in 1761,
died of yellow fever in California, on the 1st of August,
1769, at the age of 41, and this because he would insist
upon remaining an extra fortnight in the tainted district, in
order to observe an eclipse of the moon, in addition to the
passage of Venus.
Many other men of science also visited the most distant
parts of the continent, in order to take observations, and
their labour was not unrewarded, enabling them, as it did,
to determine with precision the unity of the celestial longi-
tudes, and the actual distance from the earth to the Sun.
The accuracy of their measurements will, beyond doubt, be
confirmed on the occasion of the coming passages this year
(1874), and in 1882.
M. Faye, in his final discourse as President of the French
Academy of Sciences, stated that the committee appointed
for observing this phenomenon, though much hampered by
the painful events of the last few years, had taken every
measure for obtaining a successful result.VENUS.
127
V*
It has been calculated that Yenus has an atmosphere very
similar to that of the earth as regards its extent and dif-
fractive force, the estimate being based on the shadow which
appears on the Sun’s surface a few seconds before the dark
body of Venus reaches the solar edges on the occasion of its
passage.
This observation is further confirmed by the law as to the
gradual variation of the light as it passes from the side
which is illuminated to that which is not. During 190 days
alternatively, it appears as a morning and evening star, and
though it may seem surprising that it should appear to
remain longer to the east and west of the Sun than it takes
time to accomplish its period around that luminary, this
difference is easy of comprehension when we remember that
the earth itself revolves round the Sun, and that it follows
Venus in its course, but at a lower rate of velocity.
1 Dominico Cassini discovered the fact of its rotatory
motion around an axis forming a sharp angle with the
ecliptic, which must cause, as in Mercury, a great inequality
in the days and seasons. The duration of this rotatory
motion has been fixed at 23 hours, 21 minutes, 7 seconds.
• I will conclude this chapter with a passage from the
author of Harmonies de la Nature, descriptive of this planet
and its possible inhabitants :
“ Venus must be studded with islands, each of them con-
taining mountain peaks five or six times higher than that of
Teneriffe, their sides bright with verdure and flowers.
“ Its seas must present the most attractive spectacle.
Imagine the Swiss glaciers, with their torrents, their lakes,
their meadows and their pinewoods in the midst of a southern128
ASTRONOMY.
sea; add to their sides the Loire hills, crowned with
vines and fruit-trees, and to their bases the tropical produce
of the Moluccas and the bright-plumed birds of Java.
Imagine their shores overshadowed with cocoa-trees, studded
with oyster-beds, madrepores and corals growing, amidst
perpetual summer, to the height of large trees in the bosom
of the ocean, rising above the water at the ebbing of the
tide, which lasts for 25 days, and harmonizing their scarlet
and purple hues with the verdure of the palm-trees.* And
imagine, finally, currents of transparent water which reflect
all these beautiful spectacles, ebbing and flowing from isle
to isle with a flood of twelve days and a reflux of twelve nights,
and even with all this you will have but a very faint idea
of the landscape in Venus. As the Sun at the solstice rises
more than 71 degrees above its equator, the pole which
illuminates it must possess a temperature much milder than
our spring. Though the long nights in this planet have no
moons to light them, Mercury, by reason of its brilliancy
and close vicinity, and the earth, by reason of its size, must
be more than equal to two moons.
“ Its inhabitants, about the same size as ourselves* since
they dwell in a planet of the same diameter, but in a more
favoured celestial zone, must devote all their time to love.
Some, feeding their flocks upon the hill sides, lead the life
of a shepherd; others, upon the shores of their fruitful
islands, join in dancing and feasting, and pass the time in sing-
ing or swimming for prizes, like the inhabitants of Tahiti.”
It is no exaggeration to say that in this case the imagina-
tion probably falls below the reality.
* For an accurate description of these marvels, see Eistoire des Pierres
prtcieuses, p. 139. (Firmin-Didot & Co.)CHAPTER VII.
THE EARTH.
Its origin—Its transformations—Summary of what is known concerning the
globe’s crust, by fllie de Beaumont—Cooling of the globe—Temperature
of the Celestial regions—Shape and dimensions of the Earth—Its chief
divisions: continents and seas—Proofs that the Earth is almost spherical
—Flattened shape at the Poles—Attraction—Its various kinds—Exact
date of the establishment of the law of attraction—Scientific hypothesis
as to this law—History of M. Bertrand’s measurement of the Earth—
Various motions of the Earth—Kepler, his genius and discoveries—The
seasons—Variations of day and night—History of the Earth’s translatory
motion round the Sun, by Arago.
I.
The Earth, our common mother, to borrow a term from
the ancients, has naturally been the subject of study amongst
men of science from the earliest ages.
The observations of geologists have shown that our planet
has only reached its present condition after undergoing, for
an incalculable period, numerous revolutions, traces of
which are everywhere to be found.
Everything tends to prove that the Earth was in the first
place incandescent, and has since gradually become cooler;
the existence of an internal focus is shown by the increase
of heat that takes place in the various strata of the globe
in proportion to their greater depth, and this increase is
about one degree centigrade for every thirty-two yards in
depth.
All the luminaries in our planetary system appear to have130
ASTRONOMY.
a common origin. In conformity with these ideas, it seems
rational to refer the chaos spoken of in the Bible to the
existence of a vast nebula, which, turning upon its own
axis, and very much flattened by the effect of the centri-
fugal forces caused by its rotation, would, during the suc-
cessive phases of its cooling, have cast off several of its
strata, the accumulation of which in globules, corresponding
with the separation of darkness from light, would be the
origin of the earth, the other planets, and the satellites.
This view, which is not the least inconsistent with the
strictest tenets of religion, is held by many of the most
distinguished astronomers and geologists, Father Seccbi,
director of the Boman observatory, among them. (See pp.
37 and 38.)
This theory is confirmed by all the known phenomena;
the rounded surface of the globe, the flattening at the poles,
central heat, the parallelism of the indentations which, as
M. Elie de Beaumont has proved, have been formed at each
cataclysm of the globe’s surface, the analogy with what
takes place in the heavens when stars are in process of
formation, &c., &c.
Thus the earth must have passed in succession from the
gaseous to the liquid and solid state; and even now every-
thing tends to show that, under the relatively thin crust of
49,500 yards, which we inhabit and cultivate, the substances
composing it are, if not in a liquid, at all events in a pulpy
state.
II.
Elie de Beaumont, summing up the knowledge which
we possess concerning the earth’s crust, points out that ifTHE EARTH.
131
the terrestrial rind results from the superficial cooling of
the substances in a state of fusion which originally consti-
tuted the exterior envelope of the globe, the action attribu-
table to the attractive forces upon those parts which are not
yet cool, cannot form ground for surprise. The data gene-
rally accepted as correct forbid the supposition that the
crust is more than 49,500 yards thick, or in other terms,
-yIs of the terrestrial radius. Such a shell is, by comparison,
thinner than that of an egg. Split in all directions, like
the rocks which we see upon the surface of the globe, a
vault of such slight thickness could not hold up without some
supports, and must give in such a way as to bear upon the
incandescent substances beneath it.
These substances are consequently exposed to great
pressure, which must very much reduce the mobility of their
molecules, and give them almost the properties of a solid
body. The refrigerated crust becomes, so to speak, em-
bodied with this incandescent substance, which, though not
actually in fusion because of the pressure upon it, is at
fusion temperature. Hence it results that the whole mass
of the globe undergoes the action of the attractive forces as
if it were a solid body. It must possess, however, a certain
degree of malleability, as is denoted by the remarkable
affinity which M. Alexis Perrey has shown to exist between
the frequency of earthquakes and the Moon’s phases.
The refrigerated crust of our globe, getting gradually
thicker as the cooling process continues, would eventually
acquire sufficient rigidity to maintain itself without extra-
neous support. The less refrigerated substances beneath it
would then be released from the pressure to which they are
now subjected, and an annular void might even be estab-
lished between the solid crust and the substances still suffi-132
ASTRONOMY.
ciently inflamed to remain liquid, close to their surface at
least, in the absence of any pressure. But we must hope
that the cooling of the globe has not yet reached this point,
which would probably cause a catastrophe of unexampled
magnitude. It would be due to the introduction of the sea
into the empty space between the lower and still incan-
descent surface of the solidified crust and the upper surface
of the substances still in a state of fusion.
The final phase of the relative refrigeration of the whole
mass and surface of the globe, as given by Plana, will not
be complete until 156 milliards of years, counting from the
time when the cooling process began.* The recent re-
searches of M. Poisson lead to the conclusion that all the
geological phenomena which have hitherto occurred may be
comprised in a period of a hundred million years, or even
less.f
III.
Those parts of the mineral crust of the globe which geo-
logists call sedimentary rocks were not formed all at once.
Science furnishes us with the following details upon this
subject. At one time the regions now situated in the centre
of the continent were covered on more than one occasion
with water, which deposited there thin horizontal strata of
various kinds of rock. These rocks, placed one upon
another, like the stones in a wall, must not be taken to be
all alike, and, in fact, the difference between them must
strike the least practised eye. The crystalline granitic
rocks, upon which the sea made its first deposits, have
* The printed text in the Turin Academy gives ninety-six milliards ot
years, hut the correct calculation is that given above,
f Academic clcs Sciences, first half of 1S71.THE EARTH.
133
never exhibited any vestige of a living thing. These ves-
tiges are only to be found in the sedimentary strata.
Vegetable debris is the only thing to be met with in the
oldest strata deposited by the waters, and even they belong
to plants of the simplest composition, such as ferns, rushes,
and lycopods.
Vegetation becomes more and more composite in the
upper strata, and in the most recent it may be compared to
the vegetation of the present day, with, however, the signi-
ficant restriction that certain vegetables which only exist in
the south, such as the large palm-trees, are to he found in
a fossil state at all latitudes, even in the midst of the icy
regions of Siberia.
In the primitive world, therefore, these hyperborean
countries had a temperature at least as elevated as that
of the parallels where the palm-trees now flourish ;
Tobolsk, for instance, must have had as warm a climate as
that of Alicante or Algiers in the present day. A careful
examination of vegetable substances confirms this view.
Thus, though shave-grass and rushes, ferns, and lycopods are
to he met with in the present day in Europe as well as in the
equinoctial regions, they never attain the same dimensions
in the former as in the latter countries. To compare the
dimensions of the same plants is equivalent to a comparison
of the temperature of the regions in which they grow. But
if we compare the fossil plants of our coal-producing regions
with the plants which grow in the richest parts of South
America, it will be seen that the former are far and away
the largest.
The fossil flora of France, England, Germany, and Scam
dinavia, contain ferns fifteen yards high, the stems of which
are a yard in diameter.134
ASTRONOMY.
The lycopods, which, in cold or temperate countries are
creeping plants, hardly rising four inches above the soil, and
which even at the equator do not attain a height of more
than three feet, grew to a height of eighty feet in the primi-
tive world, even in Europe. These enormous dimensions
are an additional proof of the elevated temperature which
reigned there previous to the last invasion of the ocean.
By studying the fossil animals we arrive at similar results.
Amongst the bones contained in the soil nearest to the pre-
sent surface of the globe, are the remains of hippopotami,
elephants, and rhinoceros. These remains of animals indi-
genous to a hot country, are to be found under all latitudes,
even at Melville Isle, where the temperature now falls to
fifty degrees centigrade below zero. In Siberia they are so
abundant as to have been the object of a trade speculation;
and upon the cliffs bordering upon the frozen strait are to
be found not merely skeletons, but whole elephants with
their skin and flesh in a state of perfect preservation.
Thus the polar regions have, in the course of time,
undergone an enormous process of refrigeration, caused not
by any change of the Sun, but by the dissipation of an
original heat of their own, or with which the Earth was
once impregnated. Even before the discovery of the
elephants in Siberia, science had conceived the idea that
the globe must have had a heat of its own, in proof of
which Mairan and Buffon instanced the high temperature
of certain deep mines, Giromagny amongst others.
Fourier was one of the first to examine this question,
and he pointed out the great influence of the temperature of
the celestial regions, amidst which the Earth describes its
immense orbit round the Sun.
Meteorologists had supposed, when they saw even at theTHE EARTH.
135
equator certain mountains covered with perpetual snow, and
when they observed the rapid decrease in temperature of
the atmospheric strata during a balloon ascent, that* the
regions beyond the atmosphere must be enveloped in hun-
dreds and thousands of degrees of cold. But Fourier’s
minute investigations taught us that stellar radiation main-
tains the regions traversed by the planets of our system at
from fifty to sixty degrees centigrade below zero. The tempera-
ture of the earth increases by a degree at every thirty or forty
yards depth below the surface, according to the nature of
the soil; the temperature of the air diminishes in the same
proportion at every 160 or 200 yards of altitude.
IV.
The shape of the earth is that of a spheroid, flattened at
the poles, and bulged out at the equator, the flattening
being about of the radius.
The inhabitants of the Earth, who are diametrically
opposite to each other in respect to the regions which they
inhabit, are called antipodes, as also are the places in which
they live. The point of the sky situated directly above
their heads is called their zenith, and the name of nadir has
been given to the opposite point.
The Earth’s circumference is about 24,000 miles, and
the highest mountains do not reach five miles, an altitude
which, being not quite the five-thousandth part of the
circumference, is very slight in comparison to the extent of
the Earth, and makes no more alteration in its shape than
an eminence of *03937 of an incfi would upon a globe 17 feet
in circumference,136
ASTRONOMY.
A few grains of sand upon a ball, or the unevenness upon
the contour of an orange do not prevent those bodies from
being round, and such is exactly the case with the moun-
tains upon the terrestrial surface.
The Earth’s shape is precisely that which would be pre-
sented by a fluid mass, endowed with a rotatory motion
around a fixed axis. The air which envelops the Earth
upon every side, like the solid or liquid parts which obey
the laws of gravity, must have the same shape.
In proportion as we recede from a body, the details be-
come effaced, and the main features more and more appa-
rent. Thus the Earth, as seen from a great distance, the
Moon for instance, would present the aspect of a spherical
globe, round and luminous like the Moon itself.
I will now proceed to mention the chief arguments ad-
vanced to prove that it is nearly spherical or round. To
convince us of the fact, let it be imagined that the Earth
was a plane or quite flat. In that case, as soon as the Sun
appeared upon the horizon, its light would be immediately
diffused over the whole terrestrial surface alike. This, as
we know, does not take place, and proves therefore that the
Earth is more or less convex. A vessel sailing away from
us wrould seem to decrease only in size if the Earth was
level, but, as a matter of fact, the hull first disappears,
then the sails, and, last of all, the masts; and in coming
towards us a vessel seems gradually to rise out of the water.
This can only be accounted for by convexity of the Earth’s
surface ; and as it occurs everywhere alike, the Earth must
necessarily be spherical.
Magellan, the first traveller who made the voyage round
the world, recognised this fact. Starting from Spain west-
ward, one of his vessels returned to Europe in an oppositeTHE EARTH.
137
direction, that is to say, as if it was coming from the
East.
The change in the aspect of the sky as one recedes from
Fig. 32,—The Earth, as seen from the Moon138
ASTRONOMY.
the spot which formed the starting-point is a further proof
of the Earth’s convexity. No matter in what direction we
travel, fresh stars become visible; those towards which we
advance seem to rise, and those from which we recede to
sink in the sky and at last become invisible beneath the
horizon.
The curvature of the Earth alone produces these pheno-
mena. The spherically-shaped shadow which tlie Earth
projects against the Moon when there is an eclipse of the
latter, that is to say when the Earth comes between the Sun
and the Moon, and intercepts the rays of the former, proves
to demonstration the sphericity of the Earth, for it is only
a sphere which, no matter how it is placed, can produce a
round shadow.
Fig. 33.—Phenomena produced by the sphericity of the Earth.
The flattening of the poles is also clearly proved by the
attractive influence of the Earth upon the Moon.
M. Delaunay, referring to this subject, says:—“ As theTHE EARTH.
139
Earth is a globe, slightly flattened towards the poles, and
bulging out at the equator, its influence upon the Moon
is not quite the same as it would be were it altogether
spherical in shape. There must consequently exist in
the Moon’s motion some indications of this flattening of
the terrestrial globe, and if it is possible by observation to
determine the proportions of the effect caused by this
depression of the Earth, it follows that the extent of the
depression itself may be deduced therefrom. This Laplace
demonstrated, and his calculation is almost identical with
that which has been arrived at by various measurements of
the terrestrial surface. We may even coincide with that
celebrated geometer in his opinion that a study of the
Moon’s motion is for this purpose far preferable to geo-
desical measurements, because it is the depression of the
globe as a whole, and apart from any small local irregu-
larities, which is manifested in the Moon’s motion; whereas
the geodesical measurements taken at the various points of
the Earth’s surface are more or less affected by these local
irregularities.” °
V.
If the earth is globular, how comes it that houses, men,
animals, and all the objects upon its surface keep their
balance ? Why do not the waters of the seas and rivers
run out of their beds ?
The answer is simple enough. Everybody must be ac-
quainted with the effect of a loadstone. Place some iron-
filings in close proximity to it, they would be attracted by
it, and only those upon which the loadstone failed to exer-
* Delaunay’s Annuaire du Bureau des longitudes, 186S, p. 462.HO
ASTRONOMY.
cise sufficient attractive force would fall off. The Earth
possesses force of a similar kind, by means of which it
attracts to its centre all the bodies upon its surface, and when
one of them falls it is always towards the Earth’s centre.
The fruit from its stem, the stone from the hand which
held it, fall to the surface of the Earth, impelled by that
hidden force which has been termed attraction.
This force is resident in all the bodies of nature. It
exercises its influence upon the largest masses as well as
upon the most minute particles of matter. This it is which
gives harmony to the universe, and explains the formation
of bodies of all kinds.
It makes itself felt throughout all matter just as if that
matter had no existence, so that to discern the effect pro-
duced by a spherical stratum upon a point beyond, it is
necessary to add together the influence of all its elements,
without making any distinction between those which act
directly or indirectly.
Attraction takes different names according to the kind ot
action which it exercises.
When it merely unites the different molecules which con-
stitute a body, it is molecular attraction. When it is the
invisible bond of union between the diverse elements which
constitute our globe, or the force which precipitates to its
surface the bodies which had been separated from it, it is
gravity. And, lastly, when it presides over the preservation
of the order reigning in the universe, by retention of the
celestial bodies in the limits of their accustomed course, it
takes the name of celestial gravity, and furnishes the prin-
cipal laws of astronomy.:he earth.
141
VI.
The motions of the celestial bodies, since the time when
they were first observed, accord to demonstrate the truth of
two principles discovered by Newton, which may be stated
as follows:—
1st. Bodies exercise attraction in direct ratio to their mass.
—For instance, a body weighing a pound, attracts like a
pound; if it weighs two,.its attractive force is doubled; if
three, it is trebled, and so on.
2nd. Bodies exercise attraction in inverse ratio to the
square of their distances.—The square of a number is the
product of that number multiplied by itself. Thus, the
square of 2 is 4; of 3, 9; of 4, 16, and so on. Conse-
quently, at double the distance, the attractive force is four
times less; at treble the distance, nine times less, &c., &c.
Let us suppose the mass of one body to be four times
that of another, it will attract with four times the force, and
if the two bodies are both movable, that of which the mass
is four times greater than the other will only be displaced
one-fourth as much. Moreover, if the distance separating
the two bodies is four, five, ten times greater, they will
attract sixteen, twenty-five, a hundred times less.
A body which upon the earth weighed 3,600 pounds,
would only weigh one pound if it was as far off as the
Moon; that is to say, it would be 3>600 times less attracted
by the Earth, and might, to use Euler’s expression, be held
up with one finger.
The fall of bodies to the ground follows the same laws.
If, for instance, a stone is launched into the air, there will
be a free exchange of attraction between^it and the Earth,
but as attraction is in direct ratio to the masses, the Earth,142
ASTRONOMY.
having a mass infinitely larger than the stone, will not be
displaced to any appreciable extent.
Gravity imparts equal degrees of speed to all bodies fall-
ing from the same height, whatever may be their character,
shape, or volume. This is easily proved by placing within
a long glass tube bodies of various kinds, such as lead,
cork, paper, and feathers, and then extracting the air from
it with a pneumatic machine. When the void has been
created, the tube is placed in a vertical position, and
turned upside down, when the lead, cork, paper, &c.,
descend with the same velocity as if they were one undi-
vided body. If the air is readmitted into the tube, the
lighter bodies will again be distanced by the heavier sub-
stances, and the differences between them will go on increas-
ing until the air inside the tube has acquired the density of
that outside.
M. Babinet, whose recent death deprived the French
Institute of a very valued member, wrote as follows con-
cerning the discovery of the law of attraction:—
“ In 1666, Newton, while living in retirement in the country,
gave his attention for the first time to the system of the
world. Several authors had already asserted that the law
of attraction was in inverse ratio to the square of the dis-
tance. Newton, in essaying the truth of this law by com-
paring the fall of the Moon to the fall of weighty bodies,
found it to be false, and did not, therefore, prosecute the
inquiry any further. Four years later, he ascertained, by
means of Picard’s French measurement, that this important
law was perfectly correct, and from that time, but not before,
the law of attraction was an established fact. It is well
known that when Newton received the results of Picard’s
measurements, he was so excited that he was obliged toTHE EARTH.
143
ask one of his friends to complete the simple calculation
which verified this important law, which, accurately speak-
ing, dates from 1670.”
VII.
M. Emanuel Keller has furnished the Academie des
Sciences with a paper upon the cause of gravity and the
effects attributable to universal attraction, of which the fol-
lowing interesting paragraph is an extract:—
“ Newton, during the last fifty years (1675—1726) of his
life was always studying the cause of gravity, at one time
examining its motions, at another the difference in the density
of the ether, and, though he failed to assign them their
precise places, he was anxious that nobody should suspect
him of having ever given serious belief to the hypothesis of
attraction without contact. This is evident in several of
his works, notably in the second edition of the Optics, and
in his letter to Bentley, wherein he says: ‘ It is absurd to
suppose that inert nature can exercise any action save by
contact; and the idea that gravity should be an innate
quality, inherent, essential to bodies and permitting them
to react upon each other from a distance, and with a void
between them, without any intermediary for transmitting
this force, seems to me so ridiculous that it is not worth
while to waste time in discussing it.' ”
M. Lame, in his Legons sur VElasticite, propounds the
same idea:—
“ The existence of the ethereal fluid is proved beyond
question by the propagation of light in the planetary regions,
as also by the simple yet convincing phenomena of diffraction
in the theory of undulations; and the laws of double refrac-144
ASTRONOMY.
tion prove not less surely that ether exists in all the dia-
phanous regions. Thus ponderable nature is not alone in
the universe; its particles swim, so to speak, in the midst
of a fluid. If this fluid is not the only cause of all the
facts that have been observed, it must at all events modify
and multiply them, and complicate their laws. Thus we
cannot obtain a rational and complete explanation of the
phenomena of physical nature without taking into account
this agent, always and necessarily present. And there can
be no doubt that through it will be discovered the veritable
origin of the effects attributed to calorics, electricity, mag-
netism, universal attraction, cohesion, and chemical affini-
ties ; for all these mysterious and incomprehensible crea-
tions are, after all, mere co-ordinating hypotheses, useful,
no doubt, in our present ignorant condition, but which will
be displaced by the ultimate discoveries of true science.”
From these statements, carrying great authority with
them, we may infer that gravity is to be explained by the
intervention of ether, and it is only as to the form of this
intervention that there can be any doubt. M. Keller, holds
that every weighty article is subject, in the midst of the
ether, like a vessel upon the water, to two orders of forces,
the one circular, the other perpendicular, and that the lattet
produces the motion called gravity.
VIII.
M. Bertrand, of the Institute, lecturing upon this
subject at the Sorbonne, says that the Earth has long
been known to be spherical in shape, and the ancients
endeavoured even to ascertain its dimensions. Aristotle
estimated the circumference of our globe at 40,000 stadiaTHE EARTH.
145
(a stadion is 606 feet 9 inches), which was much below the
mark, just as the calculation of Archimedes was far too
excessive. Louis XIV., in founding the Academy of
Sciences, enjoined it to ascertain the true dimensions of the
Earth; and Picard, by taking a direct measurement of
several degrees, enabled that body to arrive at a fairly accu-
rate conclusion.
In none of these experiments did anything occur to raise
a doubt as to the perfect sphericity of the Earth. But M.
Bichet, the astronomer, on his arrival at Cayenne to take
some observations, was astonished to find that the pendulum
of his clock, which marked the seconds very accurately in
France, did not oscillate so rapidly in Guiana, and he was
obliged to shorten it a full length in order to procure a
swing lasting exactly a second.
Upon his return to France, the inverse phenomenon oc-
curred, and he was compelled to lengthen it by just as
much as he had shortened it in Guiana. As a pendulum is
caused to oscillate by the force of gravity, or, in other-
terms, of terrestrial attraction, it seemed as if there must
be a diminution of gravity in the equatorial region.
Fontenelle said that this was an exception which theory
had not foreseen, but he was mistaken in this respect, as
Huyghens and Newton had indicated, and even calculated
the degree of gravity in the region of the equator. We
know, in fact, that when a body revolves around a centre
describing a circumference, there is a development of what
is called centrifugal force, which is constantly tending to
make it deviate according to the tangent from the circum-
ference which it is describing. The greater the extent of
the circumference described, the greater is the centrifugal
force.
ft146
ASTRONOMY,
We know, too, that the Earth has a rotatory motion upon
itself which takes place around an axis passing through the
poles. All bodies, therefore, placed upon the surface of
our globe describe each day a circumference, which is zero
at the pole itself, hut which increases to the equator. This
rotatory movement engenders a centrifugal force, which
causes a corresponding diminution of gravity, and the
decrease at the equator itself is ^-ro °f the weight of the
body.
Here we have one cause of the diminution in the rapidity
of the pendular swing, but it only accounts for two-thirds
of the effects remarked. We must therefore look for a
second cause in explanation of the third effect, and this
also has been indicated by Newton and Huyghens, viz., the
flattening of the Earth at the poles, on account of which an
object placed at the poles is nearer to the centre of the
Earth, and consequently more attracted than a body placed
at the equator.
Newton’s theory was universally accepted, and one neces-
sary deduction from it was that the degrees must he longer
at the poles than at the equator. But Cassini, in his
measurements of the degrees from Paris to the Pyrenees,
when executing a map of France, found that the degrees
increased in length as he moved southward. This fact he
communicated to the Academy of Sciences, which hesitated
to accept it as correct, because it was opposed to Newton’s
theory; hut Cassini, continuing his measurements north-
ward, from Paris to Dunkirk, arrived at the same result.
The conclusion, of course, was that the Earth instead of
being depressed at the poles, as Newton asserted, must he,
on the contrary, elongated; and the subject created a great
division of sentiment, one party advocating the accuracy ofTHE EARTH.
147
Cassini’s calculations, the other upholding Newton. In
order to settle the question, the Academy decided, in 1786,
to entrust the task of measuring the degrees to two com-
mittees, one of which, presided over by Clairault and Mau-
pertuis, proceeded to the polar regions; the other, with La
Condamine at its head, to the inter-tropical regions.
It is scarcely necessary to say that the arc of a meridian
extending to any considerable distance cannot be measured
with a chain like a plot of land, for, to say nothing of the
unevenness of the ground which must be taken into account,
the imperfect character of our measuring instruments would
cause the grossest errors to be made. The mode of pro-
cedure is as follows : a base not less than five miles long is
selected, choice being made of a perfectly flat surface, and
this base is measured with the most perfect instruments
obtainable. From each extremity of this base a common
point of view is fixed upon, so that the two visual rays
which reach this landmark form, with the base itself, a
triangle of which one side and two angles are known.
A simple sum in trigonometry will ascertain the three
remaining elements of this triangle, that is to say, the other
two sides and the third angle.
The proportions of this first triangle fixed, a second is
constructed in a similar way upon one side of the first;
then a third upon the second, a fourth upon the third, and
so on. In this way there is formed a body of triangles, so
placed as to be pierced by the meridian line, which it is
sought to measure, and permitting of an exact calculation
being made as to the length of this line between two given
points. The committee, after selecting a base, went on to
draw the triangles. In the course of geodesical operations
in France, a church tower was always selected as a land-148
ASTRONOMY.
mark; but this was impossible in Lapland, and there was
great difficulty in obtaining a point of view, for the country
was covered vTith forests. It was found necessary to cut
down trees upon the hill-tops, and construct scaffoldings to
act as landmarks. The Sun, too, was very scotching, and
the mosquitoes proved very troublesome. Finally, how-
ever, the triangles were completed, and the committee
returned to their starting-point to measure the base. But
in the meanwhile winter had come on, and they suffered as
much from the cold as they had previously done from the
heat. Still, by making the best use of the twelve minutes clear
light, which was all they could count upon at this season,
and assisted by the Aurora Borealis, always so frequent
during the long polar nights, they were enabled to measure
the base in seven days, and ascertained it to be 14,800
yards. They divided themselves into two parties to take
this measurement, one party measuring from right to left,
and the other from left to right, so that there might be no
mistake. Their respective measurements coincided exactly,
and the conclusion of their long labour was that the degree
in Lapland, close to the pole, was 1012 yards longer than
the French degree as measured by Cassini.
The committee despatched to the regions of the equator,
arrived at a result which coincided very accurately with the
above, for they found that the degree was about a thousand
yards shorter than in France. Thus, it was established
that the degree increases in length from the equator to the
pole.*
* Bertrand’s ClairciuH ct la Mccu.sc clc la Terre.THE EARTH.
149
IX.
Various procedures, yielding different results, have been
adopted to calculate the mean density of the Earth, and, as
a natural consequence, its weight.
Calculations based upon the attraction of mountains,
upon the pendulum, upon the torsion-balance, and the sub-
terranean pendulum, have all been employed. M. Faye, in a
communication to the Academie des Sciences (April lltli,
1873), mentions all the estimates hitherto formed, which it
may be interesting to reproduce.
Carlini and Plana, by experiments with the pendulum on
Mont Cenis, were led to put the Earth’s density at 4*39;
Maskelyne, Hutton, and Playfair, by the deviation from
the vertical on Mount Scliehallion, estimated it at 4*71;
Sir H. James, by the deviation from the vertical on
Arthur’s seat (Edinburgh), at 5*32; Reich, by Mitchell’s
torsion-balance, 5*44; Cavendish and Bailly, by the same
method, at 5*45 and 5*66; Airy, by the pendulum and a
mine-shaft, 400 metres deep, at 6*57.
MM. Cornu and Bailie have published the results of
recent experiments, whence they gather that the mean
density of the Earth is represented by 5*56; and, by a
careful interpretation of Bailly’s observations, they re-
establish a complete concordance between all the results
obtained up to the present time.
The Earth, being at a mean distance of 91,430,000
miles from the Sun, must traverse in one year an orbit of
more than 595,850,000 miles; that is 632,000 miles a
day, or 68,000 miles an hour. Such a rate of speed, though
a hundred times greater than that of a cannon ball, is
only half that of Mercury in its orbit.150
ASTRONOMY.
34.—Rotation of the Earth round the Sun.THE EARTH.
151
Owing to its rotation upon its axis, each point of the
equator travels about 24,000 miles in twenty-four hours, or
16 J miles a minute, which is about the velocity of a cannon
ball. This rotation, taking place in the direction of west
to east, gives rise to the apparent motion of all the celestial
bodies from east to west.
The Earth moves without concussion; its motion is
common to both solid and liquid masses, to the air and the
clouds, and that is the reason why we do not feel it. We
have continually the same landscape before us; the neigh-
bourhood in which we are placed invariably retains the
same situation as regards ourselves, and thus it is that we
do not remark that we change place relatively to the heavens
to the extent of 1,450,000 miles in the terrestrial orbit, and
nearly 16|- miles a minute at the equator, borne along as
we are by the Earth’s motion around its axis.
The Earth’s motion in its orbit can only be attributed
to the Sun, with which our planet is closely connected, and
which exercises its powerful attraction upon it. Its prodi-
gious mass, placed in the centre of our planetary system,
keeps up in the bodies around it the impulsion which God
gave them in the beginning, and maintains between them
that admirable equilibrium without which the wrcrld could
not exist.
' ■ X.	/	,
Kepler, the pupil of Tycho-Brahe, discovered the immu-
table laws of the planetary motions. Born in 1571, at
Weildiestadt (Wurtemburg), he was one of those rare men
of genius who work out the great theories only half pre-
pared by the labours of earlier generations. Upon the 24th153
ASTRONOMY,THE EARTH.
153
of June, 1870, a monument in his memory was unveiled in
his native town, which does not count more than two thou-
sand inhabitants. Upon the house in which he was born is
the following inscription:—“ From this modest dwelling-
place came the great Kepler, the father of untrammelled
science, who, by the power of his genius penetrated the
sublime majesty and the secrets of the Creator. This is why
so humble a spot will be celebrated in the ages which are
yet to come.”
Frisch, who has just terminated the publication of
Kepler’s complete works, begun in 1854, took for the text
of his discourse the words of the poet: “ The spot in-
habited by a great man is sacred. A century after his
death, his words and his deeds still echo in the ears of pos-
terity.” I will quote a few sentences of his remarks
“ Kepler’s genius was scarcely appreciated during his life-
time. After the publication of the works which contained
his greatest discoveries, he replied to a person who wrote to
inform him of a friend’s death; ‘I have lost my only
reader/ And he also wrote these prophetic words: * I am
quite indifferent as to whether my works are read or not
during my lifetime. I am sure they will be in a hundred
years’ time.’ Kepler’s necessities compelled him to study
astrology, which he found far more profitable than true
science. In one of his letters, he says: * Where would real
Astronomy be if she had not a harum-scarum daughter,
such as astrology? The salary of the philosopher is so
meagre, that the mother would starve unless she had the
daughter to support her! ’
“ The voluminous correspondence which he has left is full
of interest, for in it we see the man. His works reveal the
philosopher; in his correspondence we admire the noble154
ASTRONOMY.
qualities of the father, husband, and son, and liis conduct
in very trying circumstances. We love and esteem the man
who was devoted to his mother, the modest philosopher the
same with the great as he was with the lowly, who re-
mained fast to his convictions and earned respect both for
his personal and scientific merits.”
Upon a raised pedestal of elegant shape is placed a bronze
statue, about four feet in height, of the celebrated astro-
nomer. He is represented in a sitting posture, holding in
his left hand, which rests upon a celestial globe, a parch-
ment containing the drawing of an ellipse. In the right is
an open compass. The four niches of the pedestal are
filled with statues two feet high, of Michel Moesklin, the
Tubingen professor who taught him mathematics, Nicholas
Copernicus, Tycho-Brahe, and Jobst Byrg, the mechanician
who aided him in constructing his optical and astronomical
instruments. On the centre is engraved the word “ Kepler,”
and upon each side are bas-reliefs representing various
scenes in his life. On the front is engraved Physica coelestis,
and beneath is a bas-relief representing Urania measuring
space. Upon the right side is inscribed the word Mathc-
matica, and underneath is Kepler, at the age of 17, entering
upon his studies at Tubingen, under Professor Moesklin.
The latter is holding him by the hand and explaining to
him the system of Copernicus, a plan of which is given, and
a group of fellow-students is gathered around the Professor.
Two other bas-reliefs represent: one, the discussion between
Tycho-Brahe and Kepler as to the world’s system, in the
presence of Emperor Rudolph and Wallenstein, with men
engaged in printing the astronomical tables called Tabula
lludolphina; while in the other, Kepler and Byrg, in their
Prague workshop, are using their newly-completed telescopeTHE EARTH.
155
to observe the stars. Above these bas-reliefs are engraved
the words Astronomia et Optica.
XI.
M. Petit, formerly director of the Toulouse Observatory,
very truly remarks that, living upon the borders of two
centuries, during which the cosmogonic conceptions of the
human mind were very strikingly marked out, Kepler, who
lighted the torch which was destined to shed such lustre
upon the future, could scarcely be expected to escape the
prejudices created by the darkness which had gone before.
Endowed with an ardent imagination, possessed of an in-
quiring spirit, burning with the desire to achieve fame, and
originally intended for the religious profession, he was dis-
tinguished as a preacher at the age of 22; when Moesklin,
his professor, obtained for him a post as mathematical
master at Gratz, and induced him to abandon the church
for astronomy. Henceforward, led to make researches into
the first causes, he endeavoured to find an explanation for
every fact, and this is why his first works contain many’
singular theories. Fortunately for him, Tycho-Brahe, who
had settled in Germany after his twenty years* occupation
of the Dutch Observatory (see p. 26), discovered the genius
of the young astronomer by the very errors which he com-
mitted. He procured for him the appointment of mathe-
matician to the Emperor, and induced him to take up his
residence at Prague. Thus Kepler was put in possession of
the valuable materials which Tycho-Brahe had amassed, and
which were of great service to him in after life.
The following lines, written by Kepler himself, will give156
ASTRONOMY.
an idea of the enthusiasm by which he was animated in
search of truth:
“ Within the last eight months, I have seen the first ray of
light; within three, daylight; and within the last few days, the
Sun, to my great and exceeding wonder. Nothing shall re-
strain me from indulging in my enthusiasm. I wish to insult
mankind by the ingenuous confession that I have spoiled
the Egyptians of their gold, in order to create a tabernacle
for my God, far from the confines of Egypt. If you forgive
me I shall be all the better pleased, but if not, I must endure
your reproaches as best I can. Aleajacta est; I write my
book. It will be read either by the present or by a future
generation; I don’t care which. It can bide its time. Did
not God remain for six thousand years in contemplation of
his works! . . . ”
The life of this great man was far from a happy one in a
material point of view; yet he says “ I would not exchange
my discoveries for the duchy of Saxony.” And he was, of
course, quite right. Still he cannot help complaining of
“ the hard times which prevent the Treasury from effecting
a regular payment of his salary as mathematician to the
Emperor.” It was with a view of obtaining the back pay-
ments of this pension that Kepler, after putting up with
great privations for eleven years, went from Prague to
Ratisbon in November, 1631. But broken down by suffer-
ing, mental as well as physical, he was unable to resist the
fatigue of the long cold journey upon horseback, and on the
13th of that month he died, far from all his friends, at the
age of 60; and his last moments were further embittered
by the reflection that the remembrance of his name would
perhaps be of small service to the loved ones who survived
him. His presentiments, alas, were only too true; andTHE EARTH.
157
such was the fate of one who has been truly termed “ the
Legislator of the Stars.” *
The concluding lines which Kepler wrote on terminating
his works on Astronomy, reveal his great natural piety,
while they prove how much real pleasure he derived from
his studies. “ Before rising from this table upon which I
have conducted all my researches, I have but to raise my
hands and my eyes towards heaven, and address my humble
prayer to the author of all fight. O Thou, who by the
shedding of light upon nature, dost elevate our desires to
the divine light of grace, so that we may be transported into
the eternal light of Thy glory; I thank Thee, 0 Lord and
Creator, for all the joy which I have felt in the contempla-
tion of the work of Thy hands. In this book which contains
the result of my endeavours to show man the greatness
thereof, I have tried to guard against presumption, and,
so far as my limited capacities permitted, to fathom the
mysteries of infinity.” f
XII.
Kepler believed, like his predecessors, that the motion of
the celestial bodies must be circular and uniform, and he
made several efforts to prove that the motion of the planets
was the same, but, after many unsuccessful experiments, he
pierced the error which had been committed by previous gene-
rations, and arrived at the three important discoveries, since
called the Kepler Laws, which are based upon the elliptic
motion of the planets around the Sun. These laws are so
precise that they enable the calculator to name the exact
* Petit’s Treatise on Astronomy, p. 245.
f Rengstenbcrgs cv. Kerched-zig. 1S£0, p. 411.158
ASTRONOMY.
date at which a planet will return to any given point of its
orbit.
Kepler, however, was unable to discover the forces which
produced the motions he had so accurately defined. He
expended great labour upon this task, but it only resulted
in speculations far removed from the reality, and it was left
for Newton to disclose the general principle of the celestial
motions.
Just as all weighty bodies tend to the centre of the Earth,
so do the bodies which compose the solar system tend, by
force of attraction, towards the sun, which is their common
centre. But the planets, if they were governed only by
the force of attraction, that is to say, by the force with which
the sun attracts them towards him, would gradually be pre-
cipitated into that luminary; and Newton found that there
were two motive powers with which they had been endowed
by God from the beginning.
The first of these is centripetal force, which attracts or
carries the planets towards the Sun, their centre; the second
is centrifugal force, which causes them to recede from it.
These two forces counterbalance each other.
Thus, the Earth, instead of being transported to a great
distance from the Sun by centrifugal force, or dashed against
it by centripetal force, is maintained in its orbit by the
combined action of the two, and made to describe around
the Sun an ellipse, of which it occupies one of the foci.
It is to these motions in the heavens that Lamartine’s
beautiful lines refer:
Ces spheres, dont l’ether est le bouillonnement,
Ont emprunte de Dieu leur premier mouvement.
Avez-vous calculd parfois, dans vos pensees,
La force de ce bras qui les a balancees ?
Vous ramassez souvent dans la fronde ou la main
La noix du vieux noyer, le caillou du cliemin:THE EARTH.
159
Imprimant votre effort au poignet qui les lance,
Vous mcsurez, enfants, la force a la distance;
L’une tombe a vos pieds, Vautre vole a cent pas,
Et vous dites: “ Ce bras est plus fort que mon bras.”
Eli bien, si par leurs jets vous comparez vos frondes,
Qu’est-cc done que la main qui, langant tous ces mondcs,
Ces mondes dont l’esprit ne pent porter le poids,
Com me le jardinier qui seme au champ ses pois,
Les fait fendre le vide et tourner sur cux-mcmes,
Par 1’elan primitif sorti du bras supreme,
Aller et revenir, descend re et remonter
Pendant des temps sans fin, que lui seul sait compter,
He 1’espace, et du poids, et des siecles se joue,
Et fait qu’au firmament ces mille chars sans roue
Sont portes sans ornieres et tournent sans essieu ?
Courbons-nous, mes enfants, e’est la force de Dieu.
Newton did not confine his labours to the principal
planets; he calculated the motion of the satellites, and the
routes of the comets with an accuracy confirmed by subse-
quent observations. The ebb and flow of the sea, the pre-
cession of the equinoxes, the nutation of the Earth’s axis,
&c., are all effects of attraction and centrifugal force.
XIII.
The Earth is nearest to the Sun about the 1st of January,
and furthest away about the 1st of July. In the month of
January, the Earth’s distance from the Sun is 89,895,000
miles, and in the month of July, 92,965,000 miles. So that
there is a difference of nearly 3,000,000 miles. It seems
strange that the Earth should be further from the Sun in
summer than in winter, yet it is perfectly comprehensible when
it is remembered that the heat we receive from the Sun is
due, not so much to its proximity as to its elevation above
our horizon and the time it remains there. Above the 66th160
ASTRONOMY
.—The San at midnight in the north.THE EARTH.
161
degree, the Sun does not set when it has entered the sign of
Cancer. Below the 64th degree, it only disappears at
10.10 p.m., reappearing 50 minutes later, for, though in
reality it remains 8 hours and 40 minutes below the horizon,
the reflection of its rays upon the mountain-tops, and the
light shed upon the horizon by the twilight, enable one to
read and write without artificial^light.
The inhabitants take advantage of this to shoot and fish
all night, while navigators are enabled to pass through the
ice floes. Though the sun never sets in midsummer, its
light is not so brilliant in the evening as at noon; its bril-
liancy diminishes correspondingly with its disc, and becomes
mild like moonlight, so much so that one can look straight
at it without being dazzled.
These countries, which have nightless days, have also
dayless nights. In midwinter, the only substitute for the
Sun is a faint twilight, emanating from the reflection of the
rays which it lets fall upon the lofty mountains and the
thick mists that compose the atmosphere of the glacial
zone.
The nights are never so dark at the poles as in other
regions, for the moon and the stars seem to possess twice as
much light and scintillation, while their rays, reflected by
the snow and ice with which the ground is covered, shed so
bright a glow that one can see one's way, or even read with-
out the aid of a candle.
During the Sun’s disappearance, the Moon is nearly
always effulgent in these regions, and, in addition to it,
there is a continuous light in the north, the varied shades
and play of which are amongst the strangest phenomena of
nature.
The Sun, with all its varieties of light, presents us with a
M162
ASTRONOMY.
marvellous spectacle, and I shall never forget the splendour
of the sky in the polar regions, with its vast sheets of opal,
sapphire, emerald, and ruby, amidst which the Sun, after
disappearing beneath the horizon, seems to shed its brilliant
glow long after it has ceased to he visible. But I prefer to
give the reader, in place of my own impressions, an extract
from M. Marmier’s introductory speech when he was re-
ceived a member of the French Academy. He says: “ There
is a sight in the far North which, though it recurs every
year, cannot be witnessed without admiration. In summer
time, as night approaches, the Sun gradually sinks towards
the horizon. Darkness does not spread itself over the land,
hut upon the surface of the sky appears a white veil which
modifies the light, and a deep silence reigns in the woods,
the fields, and the waters. Nature is at rest. Then, all at
once, the East becomes bright with purple, the luminous
rays reappear, and motion begins again. It is the dawn of
one day which follows close upon the footsteps of the other.
As I recall to my mind this spectacle which I have so often
witnessed in Sweden and Norway, it seems to me that
nations, in their summer time, undergo phases when their
vital force seems numbed, when the Sun of their glory
seems to be departing from them. But, yet a little while,
and that immortal Sun, which no ocean can extinguish,
no darkness obscure, will shine forth again in all its
splendour.”
XIV.
Arago, in his work on Popular Astronomy, gives an a*>
count of the Earth’s translation around the Sun, of which
the following is an abridgment.THE EARTH.
163
Aristarchus of Samos (280 b.c.), insisted, as we leam
from Plutarch, that the Earth moved round the Sun, for
which he was accused of impiety.
Cleanthes of Assos (260 b.c.), is said by the same autho-
rity to have been the first to explain the phenomena of the
starry sky, by the hypothesis of the Earth’s motion around
the Sun, combined with a rotatory motion of the Earth
itself upon its own axis. This explanation, Plutarch says,
was so novel and so much opposed to the ideas generally
received, that many philosophers were anxious to prosecute
Cleanthes for impiety, as had been done with Aristarchus
twenty years before.
The planetary system of the ancients, as transmitted to
us by Ptolemy, represents the Earth as the centre around
which move the seven planets, called the Moon, Mercury,
Venus, the Sun, Mars, Jupiter, and Saturn. But while
they looked upon the Earth as the centre of the planetary
motions, and itself stationary, the ancients saw that there
was a certain distinction between the motions of the planets
and the apparent motion of the Sun, but they were unable
to disentangle the complicated details of the world’s system.
Copernicus, in the sixteenth century, endeavoured to
solve the difficult problem by reverting to the ideas formerly
expressed by Philolaus, the Pythagorean philosopher, who
had maintained that the Earth was a planet circulating
round the Sun. In his great work, De revolutionibus, Co-
pernicus began by examining whether this opinion was con-
sistent with the results of observation. He found that the
hypothesis of the Earth traversing an orbit placed round
the Sun, gives a basis by which the relative distances of
the planets from the Sun may be accurately determined,
and he was enabled to construct a system which will bear164
ASTRONOMY.
the severest scrutiny in all future time. In his system, the
Earth circulates round the Sun, taking with it the Moon as
its satellite.
To Kepler belongs the credit of having established the
true planetary system, following up the ideas of Copernicus,
upon the central position of the Sun with the planets
circulating around it, and of having abandoned the old
hypothesis, as to circular uniform motions around an imagi-
nary eccentric point void of all matter. He also dismissed
as illusionary the supposed motions in an epicycle, and con-
cluded that the Sun is the centre of the planetary motions
which take place along the circumferences of ellipses in
which it occupies one of the foci. To place this supposition
beyond the reach of criticism, and to establish it as an
immutable verity, he took infinite pains in the compilation
of a vast mass of calculations, based principally upon Tyeho-
Brahd’s observations of Mars. He succeeded in explaining
all the peculiarities of motion in that planet which had
baffled the efforts of earlier astronomers. Thus he dis-
covered the three great laws which bear his name, and which
more recent discoveries have fully confirmed.
XY.
Water occupies three-fourths of the Earth’s surface, dry
land only a fourth. There is four times more dry land in
the Northern than in the Southern hemisphere. The
Eastern hemisphere contains the largest extent of land—
about two-thirds of its whole mass—so that the sea predo-
minates in the Western hemisphere.
Internal influences have led to variations in the level of
the Earth’s crust, to which no doubt must be attributed theTHE EARTH.
165
phenomena remarked in many jdaces* For instance, in
Sweden the soil rises about two yards every century above
the sea-level; at Bavenna, the floor of the cathedral is
several inches below the level of the Adriatic, though when
the cathedral was built the reverse was the case; the palace
of Tiberius, at Caprese, is also below the sea-level, and at
Cadiz the temple of Hercules, now submerged in the sea,
is only visible at low water. The surface of the Earth is
studded with rugosities, elevations, depressions, horizontal
tracts inclined in different directions, &c. At first sight
one is scarcely able to conceive the harmony which the con-
texture of the terrestrial crust, external as well as internal,
displays to an experienced observer. It might be sup-
posed that if there was such a thing as hazard in nature,
the word might well be applied to the mountains and water-
courses, the various mines and rocks. But such is not the
case, for they are governed by laws as rigorous as those
which direct the stars in their courses.
But it is hardly twenty years since the bases of this
science, as simple as it is grand, were laid down, and to
the lamented M. Elie de Beaumont belongs the credit of
solving the puzzle and tabulating the laws which preside
over the position of mountains and the large masses on the
globe’s surface. Following in the footsteps of one who has
been termed the father of modern geology, there is no
longer any need to grope one’s way, and the details of this
science may be grasped with logical accuracy by any one
who will take the trouble to study his teachings.*
* Rapport sur le prog res de la stratigraphic, by Elie de Beaumont.1C6
ASTRONOMY.
XVI.
The embossment of the globe has a great influence upon
the climate and the nature of the soil. There are the low-
lands, consisting either of plains, undulated ground, or hills
and valleys; there are the highlands, consisting of a large
extent of elevated ground, to which the name plateau has
been given, or vast salient masses which form the
mountains.
One of the most remarkable features in the high mountains
are the glaciers, which are composed of masses of snow
that successive frosts and thaws have transformed into ice.
Their thickness varies according to their size, often exceed-
ing a hundred feet, while at certain points on the Mer de
Glace, at the foot of Montanvert, it reaches from 650 to
800 feet. These glaciers form an interesting subject for
study, and it appears from a communication of M. Grad to
the Academy of Sciences (first half of 1871) that the masses
of snow accumulated in the lofty glens of the Vosges
undergo the same transformation as glaciers far higher up
in the Alps. These accumulations form small glaciers,
which do not last very long, though it has been remarked
that their stratification corresponds to several successive
falls of snow, separated by intervals of milder weather.
Their transformation is caused by the fusion of the snow
on the surface, which, filtering into the mass, gradually
changes it into ice, more or less compact at the surface of
the soil. All these changes impart to the small glaciers
a temporary propelling motion, similar to that of the large
glaciers. This motion, appreciable even in the glaciers
where there is but a slight declivity, causes a transfer of the168
ASTRONOMY.
maximum of thickness from the upper to the lower portion
of the mass during the interval between spring and summer.
Thus the Vosges glaciers present upon a small scale the
same transformations as those in the Alps, except that their
transformations are more rapid, because of the more elevated
temperature. They are, in fact, almost at an end in the
Vosges, when they are only just beginning in the upper
regions of the Alps; as for instance, on the Col Theodule,
where, at an altitude of 9,900 feet, the glacial embryo,
when submitted to experiment, is found not to begin its
transformation until June. A remarkable fact in connection
with the glaciers, which must have been noticed by all tra-
vellers to Chamounix during the summer, is the progressive
diminution of the two principal glaciers in that valley, the
Mer de Glace and the Glacier des Bossons. Persons return-
ing to Chamounix after an absence of ten or fifteen years,
have remarked a great change, and the observations extend-
ing over a period of forty years, taken by a resident, prove
that, with the exception of partial oscillations, probably due
to the severity of particular winters, the same phenomenon
has been going on for the whole of that period.
The diminution of glaciers on the northern slope of Mont
Blanc forms a striking contrast to the encroachment of the
glaciers on the northern slope of Mont Bosa.* The co-
existence of these two facts leads to the supposition that the
oscillation of the glaciers is mainly due to local causes,
engendering either a decrease or increase of temperature.
Nevertheless, the contraction of the Chamounix glaciers
seems to be merely an instance of the elevation of tem-
perature which is said to have taken place within this gene-
* M. Key de Morande, and the Academic des Sciences, 1869.THE EARTH.
169
ration throughout various districts of Upper Savoy. Abbe
Vaullet, after forty years of thermometric observations,
regularly repeated twice a day, and by studying the growth
of plants, arrived at this conclusion so far as the neighbour-
hood of Annecy was concerned, and he attributed the change
first to the clearing of forests; secondly to the cultivation of
waste lands; thirdly, to the opening up of roads; fourthly,
to the removal of so many hedges.
XVII.
M. Grad, in a further communication to the Academy of
Sciences upon the limits of perpetual snow, makes some
valuable contributions to our stock of knowledge. Bouguer
states that this limit corresponds, all over the Earth, to the
height at which the mean annual temperature stands at zero
(centigrade). Alexander von Humboldt and Leopold Buch
fix the limit at the mean temperature of zero (centigrade)
during the summer; and M. Renou affirms that in all
countries the limit of perpetual snow is the altitude where,
during the warmest half of the year, the mean temperature
equals that at which ice melts.
M. Grad insists that what little positive information we
have is insufficient to permit of our establishing relation
between the temperature of the air and the lowest limit of
perpetual snow.
The observations taken in various parts of the Alps in-
cline him to think that the line of neves * as indicated by
Hugi, who was the first to study this question, is most
likely to be the lowest limit of perpetual snow.
* Neve is a substance half snow, half ice.170
ASTRONOMY.
Neve is snow in a grainy condition, partially trans-
formed into ice, and forming upon the surface of glaciers a
series of successive annual strata, the outlines of which are
easy of recognition. The contour of the most recent stratum
constitutes the lowest limit of perpetual snow, the precise
altitude of which has only been measured at a few points,
and the figures given in the works on geography must only
be taken, therefore, as approximative. In the Alps the
mean height is from 3,300 to 3,630 yards in the Alpe^|
Maritimes and the Alps near Cotte; 3,080 on the northern,
and 3,520 on the southern, slope of the Valais Alps; 2,860
or 2,970 in the Glarus Alps.
In the Scandinavian Alps, where the temperature is
higher, and upon the western slope, which is also exposed
to mild winds, the snow-limit, at 67 degrees latitude, is as
little as 1,100 yards ; and upon the eastern, which is both
drier and warmer, it is only 1,320 yards. Upon the
southern slope of the Himalayas, comparatively warm and
wet, perpetual snow has a limit of 5,745 yards; and upop
the eastern slope, which is both colder and drier, it is 6,130
yards. Such is also the case on many other points of the
globe. The lowest limit of perpetual snow does not, a£
M. Grad points out, depend merely upon the temperature,
for it varies very much in the same latitude, according to
the amount of snow-precipitations. The highest limit i$
6,812 yards, upon the southern slope of the Kara-Koroum
mountains in the interior of Asia, between 35 and 36 degrees
of N. latitude. Its lowest is 5,600 yards, in the Andes
near Quito, upon the equator. Upon no point of our globe
does the limit of perpetual snow reach the level of the sea,
not even in the regions where the climate during the
warmest half of the year is below zero, as in Greenland orTHE EARTH.
171
Spitzbergen. The glaciers alone descend to the level of the
sea, in 43 degrees of latitude, in Patagonia, and in 60 degrees
latitude on the western coast of America; and this is owing
to the great precipitations of snow which are caused by the
moist winds.*
The tropical countries containing high mountains possess
a very varied type of beauty, for they may be said to enjoy
all the four seasons simultaneously. Upon the summits of
the mountains glitter ice and snow, while at their feet pre-
vails a tropical heat, so that in the course of a quarter of an
hour’s walk there is a marked change of temperature. The
inhabitants profit by this valuable disposition of nature, to
have houses at two or three different altitudes, by which
means they can enjoy perpetual spring.
XVIII.
Three-fourths of the Earth’s surface are a vast sheet of
salt water. The presence of the salt is accounted for by
the supposition that the waters once covered the whole
globe, and thus dissolved all the saline masses upon its
surface. It has also been attributed to the presence of
inexhaustible salt-banks in the bed of the ocean.
Sea water, transparent and colourless when a small
quantity is submitted to examination, is very varied in
colour when looked at in a mass. At one moment its tints
are azure blue, at another emerald green. It exhibits, too,
all the colours which can be comprised between these two
tints: dark blue, grey blue, green blue, dark green, pale
green, etc.—the latter colour being especially remarkable
all along the Needles.
* Academic des Sciences, March 24th, 1873.] 72	■ ASTRONOMY.
The explanation hitherto given of the cause which gives
rise to this diversity of tints has been very unsatisfactory,
but it is certain that they are produced by matters of various
kinds which the ocean holds in suspension.
The phenomenon of the sea’s phosphorescence is one of
the most beautiful in nature. When manifested in all its
Fig. 38.—Nereus, the Sea-gocl. Panofka. Blacas Museum, plate 20.
splendour, the surface of the ocean is as magnificent as that
of the starry sky.
XIX.
The mysterious depths which separate the continents of
our globe are almost unexplored, and the science of marine
geography is yet in its infancy. We cannot carry our inves-
tigations far beyond the coast without meeting with difficulties
as yet insuperable. Still, by means of sounding, considerable
results have been achieved, and during a voyage from Eio
Janeiro to the Cape, in October, 1852, the sounding-line
attained a depth of 46,280 feet. In deep water it is
difficult to reach the bottom, but the English Channel hasTHE EARTH.
173
been so completely sounded, that navigators know every
inch of it. But the friction of the water, and the weight of
the cord itself, make it impossible to tell exactly when the
sound touches the bottom. Moreover, the cord does not
descend in a straight line, being carried in different direc-
tions by the influence of the under-currents. Thus it is
impossible to rely very closely upon the results obtained,
and it may even be wisest to discard altogether the result of
certain soundings in the Atlantic which attained incredible
depths.
The system now adopted by the American Navy seems at
once the simplest and the most accurate; A cannon-ball is
thrown into the sea, attached to a very thin cord. The
cannon-ball sinks with a gradually increased velocity until it
reaches the bottom. The cord will continue to unroll even
after the cannon-ball has reached the bottom, being borne
along by the powerful currents. Still, as the speed of
these currents is a known quantity, and incomparably less
than that of a cannon-ball projected from a great altitude,
any hydrographer is capable of distinguishing between the
two periods, and so of telling when the action of the cannon-
ball upon the cord ceases. This cannon-ball is so con-
structed that when it reaches the bed of the sea it unfastens
itself from the cord, which brings up a small cylinder con-
taining substances from the bottom. In this way, specimens
can be obtained from very deep parts of the ocean.
Nature seemed to indicate Ireland and Newfoundland as
the two starting points of the line which was to unite the
continents of which they form the advanced sentries, and
the study of hydrography led to the same conclusion. The
bed of the sea sinks very rapidly on leaving the Irish coast,
but it soon reaches a depth which varies very little most of174
ASTRONOMY.
the way across# This marine plain, called the. telegraphic
plateau, is about 9,900 feet below the level of the ocean.
More level and vaster than the steppes and deserts of our
continents, the sound has not discovered there either sand
Fig. 39.—Forammifera, brought up from the beS. of the ocean during tbe laying of
the Transatlantic Cable.
or ciay, and it is composed entirely, of the microscopic
animals known as foraviinifem• *i These animalcule, which,
during their ephemeral existence, cover the warm waters of
the tropical seas, sink after death to the bottom, and the
submarine currents carry them to these still depths, where
their delicate carapaces are perpetually shielded from the
tempests which convulse the surface of the waters.
The bed of the sea, which, in the middle of the Atlantic,
is 9,900 feet deep, gradually rises on nearing America
until Newfoundland, where it forms a steep decline, as upon
the Irish coast.
XX.
In another work, Les Mondes Scicntifiques, I mentioned
some curious experiments which had been made at Wharf-THE EARTH.
175
Road Dock, London, for the purpose of ascertaining the
effects of the pressure upon a cable submerged in the
Atlantic to the depth of two and a quarter miles. The
experiments were made with Reed’s hydraulic press, which
is capable of exercising a pressure of about 10,000 lbs. to
the square inch. The cable used was a piece of that which
has been laid in the Gulf of Persia, with a covering of
gutta-percha a centimetre (two-fifths of an inch) thick. It
was subjected for an hour to a pressure equal to that of a
body of sea-water two and a quarter miles deep, Professor
Thomson having previously tested its conductibility with a
reflecting galvanometer. Some electricians expected that
this enormous pressure (5,000 lbs. to the square inch) would
force the water into the interior of the cable, and that it
would consequently be deteriorated, if not destroyed. The
experiment did not warrant these forebodings, for it was
found that the pressure had, on the contrary, improved the
cable, at least so far as its conductibility was concerned.
It is said that a bottle of wine, carefully corked, was
plunged to a great depth in the Atlantic, and that when it
was drawn up the wine had all disappeared, and its place
taken by salt-water. Also, that a carefully-corked empty
bottle was let down, and drawn up full of water without the
cork being removed.
In another experiment, six bottles of pale ale, all care-
fully corked and covered with capsules, were let down; as
also a number of bottles of lemonade and ginger-beer, with
wire over the corks, like champagne. In one of the empty
bottles was placed a wooden cylinder, resting on the bottom
and supporting the cork. All these bottles were submitted for
an hour to the pressure of a column of water two and a
half miles deep. When drawn up, the pale ale bottles were176
ASTRONOMY*
found to be unchanged, as also were the lemonade and ginger-
beer b’ottles. The small space that had been left between
the cork and the liquid was filled up, and this was all* The
cork in the first empty bottle had been forced in, and it was,
of course, full of water. The champagne-cork in the bottle
which contained the wooden cylinder was partially forced in,
and it came up full like the rest.
These facts, due to the pressure of the water, are not
without their interest and instruction.
I will terminate this section of the chapter on “ The
Earth ” by an account of the coral bank near Haiti, which
Mr. Green, the well-known diver, contributed to the Panama
Star in 1868.
€t The bank of coral to which I allude is forty miles long
by from ten to twenty wide, and it is one of the most
beautiful spectacles which the eye of a diver ever contem-
plated. The depth of the water varies from 10 to 110 feet,
and it is so clear that one can see a distance of three or
four hundred feet when in the water. The bed of the ocean
is, in certain places, as level as a marble floor; at others, it
is studded with columns of coral from 10 to 110 feet high,
and about a foot in diameter. The summits of the highest
columns support thousands of pendants, which are in turn
decorated with thousands of still smaller ones. At other
points, the pendants form arches upon arches, and the
diver, standing upon the bed of the sea and looking through
these sinuous passages, is reminded of a cathedral sub-
merged beneath the ocean. Here and there the coral rises
to the surface of the water, just as if the loftiest columns
were the towers of majestic temples, now in ruins. There
is a countless variety of shrubs in every crevice of the coral
where the water has deposited any soil. Though of a veryTHE EARTH.
177
faint colour, owing to the small amount of light which they
receive, there is every variety of shade, and all of them differ
from the plants seen on dry land. One of these shrubs
particularly attracted my attention. It resembled a large
fan, of very varied colours and tints. The fish upon
these Silver Banks are also as varied in shape and dimen-
sions as the region which they move about in, from the
symmetrical goby to the globular sun-fish, some being of a
very dull colour, and others of a hue as changing as that of
the dolphin.**
XXI.
The temperature of the sea varies, but at the bottom it is
generally four degrees (centigrade) above zero, whatever may
be the surface-temperature. Such a temperature naturally
sets up numerous motions in this vast extent of water, which
is incessantly tending to an equilibrium.
It is possible that these motions give rise to the currents
which are remarked in the ocean, and which are vast streams
whose progress is only arrested by bodies of water denser
than themselves. It is also thought that the shape of the
land and the attractive action of the Sun and the Moon
contribute to produce these currents.
When navigators use the thermometer, they are able to
distinguish with ease the great oceanic currents of tepid
water which are encircled by the cold waters, and which,
flowing back in the track along which they came, form a
sort of interminable stream.
In addition to the great currents there are many secondary
ones, notably in the seas between the Tristan d’Acunha178
ASTRONOMY.
islands and the Cape of Good Hope. These currents are
easy of recognition, for they make the ocean look as if it
was divided into bands of different hues, and a vessel
passing through them is driven more or less out of the
straight course.
The principal of these currents, the only important one in
fact that has been thoroughly studied, is that which starts
from the Gulf of Mexico, and which extends all along the
coast of the United States to the northern region, where its
waters still maintain a relatively warm temperature, and
create a space of open sea amid the polar ice.
Mr. James Croll has published several works upon this
vast marine current, which is known as the Gulf Stream;
and he has made some interesting calculations as to the
quantity of heat which its waters are capable of trans-
mitting.
He estimates that the total volume of the waters com-
posing this stream is equivalent to a canal about fifty miles
long and 1,000 feet deep, in which the water moved at a rate
of four miles an hour. The mean temperature of this liquid
mass, when it flows from the Gulf of Mexico into the Florida
Keys, is not less than 18° 3 (centigrade).
It seems certain that these waters, when they return from
the north, have a mean temperature of 4° 4C, a diminution,
that is, of 13° 9C. Thus every cubic metre of water conveys
from the tropics to the north 13,900 calorics, representing
a dynamic force of 5,907,000 kilogrammeters, at the rate
of 425 kilogrammeters to each caloric. By the same cal-
culation, it is estimated that the current must embody
156.900.000.	000 cubic metres of water per hour, or
8.766.000.	000.000 per day. At this rate, the quantity
of heat which the Gulf Stream subtracts each day from theTHE EARTH.
179
equatorial region amounts to 52,250,000,000,000,000 calorics,
or 22,250,000,000,000,000,000 kilogrammeters.
Sir John Herschel’s and Pouillet’s researches as to the
quantity of heat transmitted directly by the Sun, show that
if a portion of it was not intercepted by the atmosphere, a
square yard, exposed to the Sun’s rays, would receive per
second a quantity of heat equivalent to 237 lbs. But
while Mr. Meech has estimated the quantity of caloric
intercepted by the atmosphere at nearly of the quantity
emitted by the Sun, M. Pouillet puts it at irV* Taking the
former calculation, we find that the heat received per second
by a square yard of ground, with the Sun at the zenith, is
equivalent to a mechanical force of 96 kilogrammeters, 2'.
If the Sun remained stationary at the zenith for twelve
hours, it would amount to 4,158,000 kilogrammeters.*
In Kohl’s History of the Gulf Stream it is pointed out that
the name of this remarkable Atlantic current dates back to
1748, when the Swede, Peter Kalm, wrote a book of travels,
in which he alluded to the debris of trees, plants, etc., which
were washed from the Gulf of Mexico to the Faroe Islands
and Iceland. The first navigator who turned the current to
his profit was Alaminos, the pilot of a vessel conveying
despatches from Fernand Cortes to Spain, in 1519. For
the next two centuries, the American whalers were the only
persons who seem to have been acquainted with it, and they,
by keeping out of its course during their voyage back from
Europe, reached America a fortnight quicker than the
English mail-packets. Franklin, when postmaster-general,
had a chart of the Gulf Stream executed by these fishermen,
and sent it to the English authorities, but they do not seem
Les Mondcs s<Mitiifiquest 1870, p. 204.180
ASTRONOMY.
to have placed any reliance upon it. Franklin, too, was the
first to take steps for ascertaining the course followed by tlie
current, which he did by finding out in what parts of the
ocean the water was warmer than elsewhere.*
XXII.
M. Grad, in a communication to the Academy of Sciences
(1871), points out that if the nature of this marine current
is understood over the first half of its course, such is not
the case in the northern half. Flowing from the Gulf of
Mexico into the Florida Keys, it runs parallel with the
coast of the United States as far as Cape Hatteras. In this
part of its course, the temperature is nowhere less than
25 degrees (centigrade),* and is frequently higher, even in
winter, when, upon the African coast, of the same latitude,
the mean January temperature is only 12 degrees. After
leaving Cape Hatteras, the Gulf Stream deviates eastward
from the American coast towards Newfoundland, where, at
42 degrees western longitude from Paris, its temperature
varies between 19 and 24 degrees (centigrade) from the
months of January to July. Its waters then flow in a north-
easterly direction, embracing the coast of Europe and the
heart of the Polar Seas. But for the Gulf Stream, the
climates of England and Germany would be as inhospitable
as that of Labrador: the Scandinavian peninsula would be,
like Greenland, a mass of ice. The northern part of Norway,
where the sun is invisible for a whole month, would be so
cold that mercury would freeze there, as is the case in the
same parallel in Asia and America; whereas, thanks to the
* Cosmos, 1868, p. 205.THE EARTH,
181
Gulf Stream, the sea at Fauholnn has a temperature of more
than three degrees (centigrade) above zero. Thus, the Gulf
Stream is a permanent source of heat, which Mr. James Croll
estimates as equal to the quantity emitted by the Sun over a
surface of five million square miles at the equator.
Following the march of the temperature at the furthest
ramifications of the Gulf Stream, the author gives the pro-
portions of the warm current to the limits of the stationary or
floating ice between Greenland and the north of Europe for
the last two years. The results of frequent soundings show
that the Gulf Stream touches the bottom of the Atlantic
Ocean between the Hebrides and the Faroe Islands, at
60 degrees latitude, with a temperature of 5° ‘3 at a depth of
770 fathoms. A degree further north, between the Faroe
and Shetland Islands, the current is only 200 fathoms deep,
and the colder water of the polar regions extend beneath it
to a depth of 640 fathoms. Further north still, at 60 degrees
latitude, Admiral Irmenger found that at 60 fathoms depth
there was a temperature of 7° *5, as against 10 degrees at
the surface.
The waters of the Gulf Stream, as M. Grad proceeds to
state, then divide into two arms, one flowing northward
along the western coast of Spitzbergen, the other eastward
along the shores of Nova Zembla. The western, or Spitz-
bergen, arm reaches as far as 80 degrees latitude in summer,
where it has a temperature of two degrees (centigrade). The
limits of the Gulf Stream are more clearly defined in winter
than in summer, and the motion of the floating ice ceases
during the cold season, as out of a hundred avalanches
encountered by vessels in the North Atlantic, ninety were
met with in the months between April and August, and ten
only during the remainder of the year. The tepid waters of40.—The principal rivers of the Globe, from the Atlas of MM. Drioux and Op. Leroy (libr. Eug. Belin.)..
18a
ASTRONOMY.
5*
Caspian Sea
Black Sea
Black Sea
German Ocean
Baltic Sea
Baltic Sea
Siberian Sea
Mediterranean Sea
Baltic Sea
English Channel
White Sea
Adriatic Sea
Mediterranean Sea
German Ocean
Mediterranean Sea
Blue Sea
Sea of Okotsk
Siberian Sea
Yellow Sea
Bay of Bengal
Do.
Sea of Oman
Persian Gulf
Lake Aral
Persian Gulf
Dead Sea
Southern Ocean
Murray
Murray
Mediterranean
Gulf of Guinea
Atlantic Ocean
Do.
Do
Mediterranean Sea
Mississippi River
Gulf of Mexico
Atlantic Ocean
Do.
Do.
Pacific Ocean
Mississippi River
Gulf of California
Pacific. Ocean
Atlantic Ocean
Do.THE EARTH*
183
the Gulf Stream penetrate into the middle of the polar
seas as far as 80 degrees latitude to the west of Spitzbergen,
and as far as 76 degrees latitude on the western coast of
Nova Zembla. In some of the extreme ramifications of the
Gulf Stream there are spots where the water is colder, and
as it moves slowly there is some difficulty in ascertaining the
direction of the currents. But, notwithstanding these diffi-
culties, the fact of the Gulf Stream extending as far as
Nova Zembla has been proved by the presence of timber,
bamboo-canes, etc., which must have been floated thither
from Brazil; as also by the picking up of nets, and other
fishing apparatus, drifted from the Loffoden Isles, or
Finmark.
In a note to the Academy of Sciences, 1871, M. Marie Davy
points out that the meteorology of Europe is regulated by
the atmospheric circulation, aixd by the marine circulation
which it engenders. He insists that the main regulator of
the climate in France and the neighbouring countries is the
aerial stream, known as the equatorial current, in its first
part, and the polar current in its latter part. The efforts of
the meteorologist must, therefore, be concentrated upon the
study of this great current: its origin, the causes which
affect its quantity, as well as the direction and amplitude of
its trajectory, and the laws which govern these changes,
together with the signs which denote their being about to
take place. He must also study the origin, nature, laws,
and premonitory signs of the local phenomena which occur
within the moving aerial mass, and are the causes of so
much variety in the meteorology of Europe; and, lastly, he
must study the fluctuations of the Gulf Stream, which
result from the fluctuations of the aerial current, and react
in their turn upon the latter.184
ASTRONOMY,
XXIII.
Rivers generally follow the direction of mountains and
flow from east to west, though there are few whose course is
either, northward or southward. Several of the largest
rivers—such as the Nile, the Indus, the Po, etc.—overflow
their hanks at certain seasons of the year.' Nearly all the
ancient poets ascribed to, these rivers the honours of divinity.
Painters and poets alike represented them as venerable old
men, with long flowing beards and a crown of rushes upon
their heads. Reclining among the reeds, their hand rested
upon a pitcher with water flowing from it, the pitcher being
more or less out of the perpendicular, according to the
rapidity of the river represented. Upon medals these
divinities are placed right, or left, accordingly as the rivers
which they typify flow east or west. Every river had its
peculiar characteristic, generally taken from the animals
indigenous to its basin, or the fishes in its water.
Fig. 41.—Rliea (from an Adrian medal).CHAPTER VIII.
THE MOON.
Mature of the Moon—Its size—The light which wo receive from it when it is
at its brightest—Heat reflected from the Moon ; history of the discovery
—Shadows, spots, craters, mountains, and extinct volcanoes, observed
upon the Moon’s disc—Its various motions—Sidereal revolution—Sur-
prising velocity of the Moon’s motion—Is it possible for the Moon to fall
on to the Earth—Successive applications of the principle of gravity in
explanation of, the solar system—Problem of the three bodies—Simple
and easy experiments in explanation of the Moon’s phases—Ashy light
—Symbolisation <?f the Moon; curious passage from Sophocles.
I.
• The Moon is, next to the Sun, the celestial body most
calculated to arrest our notice, both in respect to its apparent
size and the peculiar phenomena which we see during its
course.
Though it appears to us much larger than the stars, it is
in reality smaller than any one of them, and its appa-
rent size is caused by its relative proximity to the Earth,
from which it is distant only 238,798 miles. The diameter
of the Moon, which does not always seem to us the same,
for this luminary is at one time nearer to us than the other,
is 32 minutes; that of the Earth seen from the Moon would
be 1 degree 54 minutes. The diameter of the Moon is
2,153 miles; its circumference, 6,500; its surface, only T'-r
that of the Earth; its volume, ; its mass, Like the
Earth, it is an opaque body, having no light of its own, but
receiving and reflecting that of the Sun. We see it at its186
ASTRONOMY.
brightest wheil it is full, and its light has been calculated
even then to be only that of the Sun.
Volpicelli, in a communication to the Academy of Sciences
(first half of 1870), gives some interesting facts relative to
the heat emitted by the Moon. He says that Melloni was
the first to furnish experimental proof of this phenomenon,
which Virgil, Dante, Guarini, and other Latin or Roman
poets, had denied. Many philosophers, such as Aristotle,
Thomas Aquinas, Pic de la Mirandole, and Jerome Cardan
among them, asserted the contrary; but in default of the
thermometer by which the fact has since been ascertained,
they were unable to prove that statement. The English
philosopher, Hooke, points out how feeble is the direct
calorific effect of the Moon upon the Earth. Montanori,
of Modena, states that by means of an air-thermometer and
a large mirror it was ascertained that the radiation of the
Moon caused a rise of several degrees in the temperature.
But as he does not state how the experiment was conducted,
and as the thermometer was during his time still very im-
perfect, Volpicelli discredits his assertion altogether, and
believes that he is justified in saying Melloni was the 1
first to give experimental and incontestable demonstration
of the heat of the Moon’s rays (March 23rd, 1846).
This discovery was attended with greater difficulties than
might at first sight have been expected; for the most sensi-
tive of thermometers, placed in the focus of a mirror or an
eye-glass is incapable of manifesting the existence of heat in
the solar radiation. The latest experiments of M. Bailie,
conducted by means of an ingenious apparatus, which I
have no space to describe here, corroborated as they are by
the experiments of Lord Rosse, Piazzi Smyth, and Marie
Davy, show that the full Moon at Paris emits during theTHE MOON.
187
summer months the same quantity of heat as a black sur-
face of the same size kept at 100 degrees (centigrade) and
88 yards distance.
II.
The Moon’s surface is covered with black spots, which
are visible to the naked eye, and which cause reflections of
light, varying according to the position of the Moon in
respect to the Sun. Seen through a telescope, they are far
more numerous, extending all over its surface, and present-
ing a volcanic character like the crater of Vesuvius, or
the hilly ground in the department of Puy-de-dome (France).
Some of these points have the aspect of lofty mountains,
chiefly distinguishable by the triangular shadow which they
reflect in the opposite direction to the Sun.
As a general rule the mountains of the Moon seem loftier
than those of the Earth. Many of them are thought by
astronomers to be twenty-five or thirty thousand feet
high, whereas the loftiest of tin* American Cordilleras is
only four miles (22,120 ‘ feet) above the level of the sea.
At certain times one can distinguish, beyond the limit
of the Moon’s light, brilliant points, which seem to be
detached from its disc, as if they were stars situated close
to it, They are, in reality, mountains in the obscure part
of its surface, but so lofty that their summits are lighted by
the Sun, while their base remains in obscurity.
All these asperities and unevenness of surface explain
the indentations often visible upon the bright edge of the
Moon. These indentations have often been mistaken for
volcanos, though M. de Crety, while watching the eclipse at
Aden, on the 18th of August, 1868, believed that he could188
ASTRONOMY.
distinguish, subsequent to the totality of the eclipse, three
triangular prominences upon the edge of the Moon, with
which they kept close order, and which seemed to be lunar
volcanos in a state of activity. Judging from the descrip-
tion given, these prominences must have been gaseous, or
at all events formed of very divisible matter. This appari-
tion is not, necessarily, an optical illusion; it has. been
thought to indicate the existence, upon the posterior surface
of the Moon and close, to the edge,, of a chain of volcanos
in a state of activity at the moment of the eclipse, and that
their smoke and ashes must have been hurled beyond the
edge by some unknown force, with the nature of which we
are still unacquainted.
III.
Galileo first attempted to measure the height of the lunar
mountains, and his example was followed by many other
astronomers, so that their altitude was known even before
that of many mountains of the Earth. Hevelius, in his
chart of the Moon, adopting the height assigned by Galileo
to the lunar mountains, gave to them names taken from
geographers, fearing to create a feeling of jealousy , if he
bestowed upon them the names of rival astronomers, but
since that time a different system has been followed.
M. Petit, of the Toulouse Observatory, in his work upon
astronomy, says that, after a careful inspection of the shape
of the shadows in the Moon, and that of the heights which
project them, it is easily seen that most of those heights
are composed of a circular enclosure, the inner part of
which is. generally lower than the mean surface of the Moon,WESt
189
THE MOON.
Grater of Albategnius.	Crater of Eratosthenes.
Fig. 42 represents the full Moon as seen through a powerful glass. (Guynemer.
Explanation : The capital numbers begin at the top to the left.
Marshes, Seas, LaJceSy Gulfs, Ac.
I. Glacial Sea.
. II. Gulf of dew.
lit. Gulf of flowers.
IV.	Marsh of fogs.
V.	Sea of rains.
VI.	Carpathian mounts.
VII.	Ocean of tempests.
Ylir. Midland Sea.
IX. Sea of clouds.
IX.	& Sea of vapours.
X.	Sea of darkness.
XI. Altai mountains.
XII. Sea of fertility.
XIII.	Sea of tranquillity.
XIV.	Sea of sleep.
XV. Sea of severity.
XVI. Lakes of dreams.
XVII. Lakes of death.
XVIII. Humboldt Sea.
A.	Black Lake.
B.	Valley of Endymion.190
ASTRONOMY.
and in about the centre of which is often noticeable a
column (pitori), which seems to have been formed, like the
circular enclosure itself, by matter originally depositing
itself in horizontal strata.
These enclosures mostly appear to be of very large dimen-
sions. Some of them, notably those called Eiccoli, Ptolemy,
Clavius, and others, have diameters of 130 or 140 miles,
and it is a manifest proof of their depression that the
shadow falling upon their inner surface is generally greater
than the shadow which they cast outward. There are few
circles of this kind upon this Earth, though there is one at
Cantal (France), with a diameter of 33,000 feet, and
another in Ceylon, which, though nearly forty times larger
than the first, is yet much smaller than several of the lunar
circles. Their size may perhaps be due to the fact that as
the gravity in the Moon is only a sixth part that of the
Earth, the external envelope cannot offer a sufficient resist-
ance, as that of the terrestrial globe does, to the dislocating
causes. These circles are connected with the action of
Fig. 42—continued.
Mountains, Volcanoes, Craters, Enclosures,
Height,
metres. %
1. Plato, one.	.	.	. 2,210
2.. Laplace, cap.	.	.	.	3,000
3.	Archimedes, circle	.	.	.2,300
4.	Huyghens, mount	.	♦	.	4,500
5.	Aristarchus, enc.	.	.	2,300
6.	Kepler .	.	.	.	3,600
7.	Copernicus, circle 25 leagues
in diameter.
8.	Eratosthenes, crat. .	. 4,780
9.	Grimaldi, hollow.
10.	Lalande, mount.
11.	Herschel .	.	.	.	2,900
12. Gassendi	.	,	. 2,900
13.	Ptolemy ....	2,300
14.	Longo-Montanus.
15.	Tycho, circle 70 miles in
diameter.
Height
metres.
16.	Casalus, circle.	•	•	6,900
17.	Newton, crat.	.	.	.	7,200
18.	Scliort, enc. .	.	.	5,940
19.	Curtius .	.	.	-	0,770
20.	Boussingault, crat., mount.
21.	Humboldt, crat., mount.
22.	Guttemberg enc.
23.	Albategnius, crat.	.	.	4,330
24.	Hipparchus, crests, mounts
25.	Arago, ence., mount.
26.	Geninus, crat.	.	•	•	3,700
27.	Collipus, crat..	.	.6,215
28.	Aristotle, mount • . 3,260
29.	Eudoxes, crat.	•	.	4,820
30.	Cassini, mount.THE MOON.
191
central heat, but more as craters of sublevation than craters
of eruption.	.	e
The Moon, like our globe, presents evident traces of
successive geological revolutions. Thus, around several of
the circular enclosures there is a second one, very much
smaller and evidently formed out of it. In many cases,
too, it seems as if the peak or peaks which tower above the
large enclosures had been formed subsequent to a primary
appearing. The enclosures themselves are generally con-
nected with each other, by lines of hills, as if the subterra-
nean gases had produced in the Moon effects analogous to
those observed upon the Earth, and had upheaved the
soil between the points where there was a complete
disruption.
There is nothing to show that the Moon possesses an
atmosphere, and if there was one it would be perceptible
during the occupations of the stars and the eclipses of the
Sun.
The climate must, therefore, be very extraordinary, pass-
ing without transition from a fortnight’s heat greater than
that of the equatorial regions to a similar period oi cold
more intense than at the North Pole. It seems impossible
that, in the complete absence of air, the Moon can be peo-
pled by beings organised like ourselves, nor is there any
sign of vegetation or of any alteration in the state of its
surface which can be attributed to a change of seasons.
XV.
The Moon has three principal motions# The first is
annual, round the Sun, and is accomplished in the same
time as that of the Earth, inasmuch as this motion of the192
ASTRONOMY.
Moon is but a necessary corollary of the annual revolution
of our globe. This motion is analogous to that of a stone
placed in1 a sling, which a person moving very rapidly
whirled above his head.	: • *
The second,motion of the Moon is rotatory, upon its own
axis, and is executed; in 27 days, 7 hours, 43 minutes, 11
seconds. It takes precisely the same time -to accomplish its
third motion, which is a revolution round the Earth. Heiice
it is that we always see the same hemisphere^ and. that there
is consequently only one day and one night in a lunar
month.	,	.	. •
The Moon circulates incessantly in a re-entering curve,
within which is placed the Earth. It never leaves our
globe, whence its name of satellite.	.
The term duration of the sidereal revolution is used to
describe the time which the Moon takes to come back to a
particular star. At the commencement of this century the
duration was 2,732 solar days, but it is not; the same in
every century, having gradually been on the decrease ever
since observations were first taken.
Halley first noticed that the motion had been accelerating
from the earliest times, notably since the observations taken
by order of the Caliphs.
At first sight this seems very astonishing when taken
in connection with the laws which regulate the celestial
motions, for it is impossible for one body to move around
another at greater rapidity without diminishing the distance
between them. If the Moon moved more rapidly than the
Earth, it must be getting nearer to us, so that if this speed,
increased to an indefinite extent, the Moon would fall on to
our globe and' cause terrible revolutions in the present order
of things.0
THE MOON.	193
Fig. 43.—The Moon’s phases.
o194
ASTRONOMY.
The consequences of the acceleration remarked in the
Moon’s motions were discussed at great length by the astro-
nomers of the eighteenth century, but the public heard
nothing of it until Laplace demonstrated theoretically that
the acceleration would be confined within very narrow limits,
and would be succeeded in the course of time by a corre-
sponding degree of retardation.
Ossian, in a.passage of his poem, Darthula, also alludes
to the popular superstition as to the fall of the Moon to the
Earth.
y.
M. Delaunay, writing to the Academy of Sciences, attri-
butes the apparent acceleration of the mean motion of the
Moon to the progressive slackening of the Earth’s revolu-
tion upon itself, owing to the influence of the Moon upon
the waters of the sea. In his Report upon the Progress of
Astronomy, he says: “ It was already known that the mean
motion of the Moon may be seen to undergo a great change
owing to some variation in the rotary speed of the Earth,
that is to say, in the duration of the sidereal day, which is
the fundamental unity of time in astronomy. I have shown
that in the action of the Moon on the sea-water, taking into
account the phenomenon of tides, and more especially the
retardation of high tide during the Moon’s passage over the
meridian, there is enough to occasion a progressive slacken-
ing of speed in the Earth’s rotary motion to an extent
that would account for the secular equation of the Moon,
which is not to be explained by the theory which Laplace
assigned for it.”
Little relation as it may at first appear there is betweenTHE MOON.
195
the general temperature of the Earth and the motion of the
Moon, the result obtained by Laplace has helped to show
that the temperature lias not varied the hundredth part of
a degree for the space of two thousand years.
Perigee is the point in the orbit of the Moon which is
nearest to the earth, as opposed to apogee, which is the
farthest.
The variations of the Moon’s proper motion and the
changes in distance are connected by that very simple law dis-
covered by Kepler, to the effect that “ the surfaces described
by the lunar radius vector are equal at equal times; and
from a given radius vector they are proportionate to the
times.” A radius vector is a straight line from the Earth to
the Moon. Bouillaud, in explanation of the inequality in
the Moon’s motion, that great discovery of Ptolemy, attri-
buted it to a displacement of the focus of the lunar ellipse;
whence the name of erection or displacement which has
remained to this day.
VI.
I will complete my notice of the Moon by a summary of
what M. Delaunay has set forth in his great work upon this
subject, from which also we shall be able to deduce the suc-
cessive applications of the principle of gravity in explana-
tion of the solar system.
Newton endeavoured to establish the identity of terrestrial
gravitation and the force which retains the Moon in its orbit
round the Earth, but he had not the necessary elements for
obtaining an affirmative solution. Picard, a member of the
Academie des Sciences, undertook the task of taking an
accurate measure of the Earth’s dimensions, and by this
means he ascertained that the terrestrial radius had been196
ASTRONOMY.
thought much greater than it in reality is. Newton, in
1682, sixteen years after his first essay, heard of Picard’s
process, which enabled him to evolve the law of gravity
(see page 158), by virtue of which “ two bodies attract
each other proportionately to their masses, and in inverse
ratio to the square of their distance.*’ He naturally sought
to generalise this law, and see whether it would explain the
phenomena presented by the motion of the bodies which
occupy space. The Moon furnished him with a means of
regulating his inductions. He arrived at the conclusion that if
the Sun did not exist, the Moon would revolve round the
Earth, while remaining in the same plane of position, that
it would describe in this plane an ellipse with one of its foci
at the Earth’s centre, and that the great axis of this ellipse
would not change place with the change of time.
But the Sun, exercising its attractive influence alike on
the Moon and the Earth, makes the motion of the former
around the latter very different. Newton pointed out that
it was this influence of the Sun which causes the retrograde
motion of the lunar nodes, the direct motion of its apogee,
the nutatory motion of the lunar orbit, and the periodical
inequalities which cause the Moon to oscillate right and left
from the position which it would occupy if it followed to the
letter the laws of elliptic motion.
He also showed that the same law of attraction, which
furnished an explanation of nearly all the circumstances
relating to the motion of the Moon, accounted in a very
natural way for the phenomena of tides, and that this
periodical oscillation of the surface of the seas is due to
the differences in the action of the Sun, and especially of the
Moon, upon the whole mass of the terrestrial globe and the
waters which form part thereof.THE MOON.
197
VII.
M. Delaunay goes on to remark that one of the first
questions which the geometers set themselves to resolve
was the problem of the three bodies; that is to say, given the
existence of three bodies, the Sun, the Earth, and the Moon
in space, what is the motion of each under the simultaneous
action of the other two ?
Clairaut, d’Alembert, and Euler each studied this question,
about the middle of last century, and each made consider-
able progress towards its solution. One of the first results
which they obtained was the explanation of erection—an
inequality which Ptolemy had discovered more than nineteen
centuries since, and which Newton had failed to make harmo-
nise with his great law of gravity. This inequality, when
explained, ceased to form an exception, but became, like
the other inequalities which were previously known, a
natural consequence of the perturbing influence exercised
by the Sun upon the Moon.
The calculation of the perturbations of the planets due
to their mutual action upon each other had shown that the
elliptic orbit of the Earth slowly alters in shape; that the
slight difference now existing between its orbit and a circle
is gradually disappearing, or, in other words, that its eccen-
tricity is decreasing. The consequence of this is that a
progressive and very gradual change takes place in the
annual distances of the Sun from the Earth and the Moon.
This change leads to a corresponding variation in the dis-
turbing action of the Sun upon the Moon.
Laplace saw that this must cause a progressive accelera-
tion of the Moon’s motion around the Earth, and he found198
ASTRONOMY.
that the sum of the periodic equation due to this cause har-
monised with that which had been deduced from a com-
parison of ancient with modem astronomical observations.
After such successful calculations it was impossible to
question the truth of Newton’s great law, and so his magni-
ficent conception of an unique cause governing the various
motions of the stars as well as the fall of a body to the
earth was fully realised. The law of universal gravity be-
came the principal base of the subsequent progress in astro-
nomy, for, previous to its establishment, the researches con-
cerning the motions of the planets were entirely conjectural.
This great discovery, establishing a bond of union between
all the details of these motions, gradually led up to a more
precise knowledge of them, which may be almost indefinitely
perfected#
VIII.
The most curious phenomenon and the one earliest ob-
served in regard to the Moon is that of its phases. The
theory of the phases is simple, but by means of an experi-
ment that any one can try, it becomes still more so.
If a wooden or cardboard globe, painted white, is exposed
to the light of a candle, it will be found that one half of it
will be illuminated while the other half will remain in the
shadow. The spectator, changing his point of observation
in respect to the globe or the candle will see more or less of
the illuminated half, and more or less of the half which
remains in the shadow, thus witnessing a series of phases
similar to those presented by the Moon.
Standing opposite to the candle, only the obscure hemi-
sphere will be visible; starting from this point, and describ-THE MOON.
199
ing a quarter-circumference round the globe, half of the
illuminated part, which will look like a semi-circle, becomes
visible.
Standing between the globe and the candle in such a
posture as not to intercept the rays of the latter, the illu-
minated half will be visible in full. Making a third revolu-
tion of a quarter-circumference, another semi-circle, the
reverse of the first, will be visible, and, coming round again
to the starting point only the obscure half will meet the
eye.
In this way the observer will have seen the four principal
phases of the Moon, but if instead of moving round the
globe he has the globe moved round him, the phenomena
will remain exactly the same, supposing him, that is to say,
to turn his body round as the globe is made to revolve.
A still more remarkable effect will be produced if, instead
of obtaining the light and shadow from a candle, the ex-
periment is made with a globe of which one half is painted
white and the other black. Bearing in mind these pheno-
mena, the following explanations concerning the Moon’s
phases will be found very easy to follow.
IX.
When the Moon is first seen in the evening, it has the shape
of a narrow crescent, the convexity of which is circular and
facing the Sun, and the concavity slightly elliptical and
facing the east.
The width of the crescent gradually increases; half of
the luminous part of the Moon becomes visible at the expi-
ration of seven days, having accomplished a quarter of its
course, which occupies twenty-nine days. This is, conse-200
ASTRONOMY.
quently, the first quarter, and, crossing the meridian at six
in the evening, it continues its course eastward, the lumi-
nous part becoming larger every day, and appearing, to us
almost elliptical or oval in shape.
Seven and a half days later, all the luminous hemisphere
becomes visible, and this is called the full-moon, which
rises in the east as the sun sets in the west. It crosses the
meridian at midnight. In the interval between full moon
Fig. 44.—The lunar crescent, six days after a new Moon.
and the last quarter, the full moon wanes in exactly the
same manner as it had increased; its shape becomes elliptic
until we can see no more than half of its disc.
It is then in its last quarter, and does not cross the meri-
dian till six in the morning, and this is why it is visible inTHE MOON.
201
the heavens during the greater part of the day. From the
last quarter the luminous part continues to decrease until
nothing is visible except a crescent, which appears in the
east before sunrise, its horns turned up and opposite to the
Sun. This crescent then disappears, and is succeeded by a
new. moon, so called because it comes between the Earth
and the Sun, with its luminous hemisphere turned towards
the latter.
The faint light shed over all the obscure part of the Moon
during the first and last days of the crescents is, like the
phases, caused only by the motion of the Moon, and its
situation relative to the Earth.
The Earth reflects the light of the Sun upon the Moon,
just as the Moon reflects it upon the Earth. So when the
Moon is new, the Earth is exactly the opposite (being full
Earth for the Moon), and transmits it so much light that the
Moon retransmits a portion of it by reflection; and hence it
is that the whole of the disc becomes visible at dawn and
sunset.
Thus the light which passes from the illuminated hemi-
sphere of the Earth to the obscure surface of the Moon be-
comes reflected, returns in a fainter form to the Earth, and
makes visible the half of the Moon, which is not only edged
with a silvery crescent, but is of a pale and ashy tint
throughout, which causes it to stand out against the azure
blue of the sky.
This phenomenon, known as that of earthshine {lumen
mcinerosnm), ceases as the Moon grows older, for then only
a small portion of the luminous hemisphere is turned to-
wards it. Most of these phenomena are indicated in Fig.
43 (p. 133).ASTRONOMY.
202
X.
M. Janssen, noted, for his experiments on spectrum ana-
lysis, has published an account of his escape from Paris in
a balloon during the German siege, in order to witness the
eclipse on the 22nd of December, 1870. The account con-
tains certain passages bearing upon our subject, which are
worth record. Leaving Paris at 6 a.m. on the 2nd of De-
cember, the thermometer marked 1 degree (centigrade)
below zero. The sky was very clear, and after sunrise the
thermometer declined to 7 and 8 degrees below zero. Thus,
the apparition of the Sun instead of creating an increase of
heat, and so of ascension for the balloon, exercised a directly
contrary effect, which, strange as it may at first seem, is
easy of comprehension. The effect of the solar radiation
was to dissipate the atmospheric vapours, to increase the
transparency of the atmosphere, and so to augment very
considerably the radiation of the balloon towards the celes-
tial regions. In this process the balloon expended more
heat than it received from the Sun, and its refrigeration
tended to make it descend.
M. Janssen adds: “ This action of the first solar rays
upon the vapours of the atmosphere, remarked so clearly in
the very regions where it took place, is a fresh proof and a
very strong one in support of the theory that the Moon is
capable of dissipating vapours and light clouds. In this
respect the traditions of farmers concerning the April moon,
those of the Hindoos as to the agency of the stars in the
formation of ice, and other analogous ideas, seem far nearer
the reality than scientific men have been inclined to believe.
Even if its rays do not freeze plants or congeal water in a
direct way, they may nevertheless be regarded as the indi-\
TOE1 MOON.	203
rect authors of this phenomenon, if they pierce the atmo-
spheric veil which protects vegetation and sustains terres-
trial heat.”
The Moon has always been the symbol of capriciousness
and change. Sophocles, in a tragedy which has been lost
to us, but of which Plutarch cites a fragment, makes Mene-
laus say: “-But my destiny, placed upon the rapid wheel of
fortune, is ever revolving and incessantly being transformed.
Thus, too, the aspect of the Moon is never the same for
two whole nights consecutively.. Yesterday it was not
visible, but suddenly it begins to show itself; gradually its
visage brightens, and expands every day. And, after shining
in all its splendour, it begins to wane, and finally dis-
appears.” *
* Life of Demetrius, p. 173.
CHAPTER IX.
THE ECLIPSES.
Principal eclipses— Occultation—-Theory of tlie eclipses of tlio Sun and tho
Moon—Partial, total, or central eclipse—Appulse—Luminous cor.ma,
protuberances, prominences, rose-coloured flames noticed during eclipses—
The most remarkable solar eclipses—Measure of tlie eclipses—Im-
mersion and emersion—History of the information about eclipses from
what has been remarked during their occurrence—Terror which eclipses
formerly inspired—Curious facts—Meton’s cycle—The golden number—
Saros—Instruments for indicating past and future eclipses—The utility
of eclipses in fixing doubtful dates—Historical facts— Christopher Colum-
bus and the islanders—Pericles and his pilot—Pelopidas and an eclipse
of the Sun—The soldiers of Paulus Emilius and an eclipse of the Moon-
Terror of Nicias, the Athenian general—Remarkable passage from Plutarch.
I.
The principal eclipses are those of the Sun and the
Moon. Eclipses of the planets, of their satellites or
secondary planets and of the stars also take place, but the
latter are generally termed occultations.
There is an eclipse of the Moon when, the Earth being
interposed between the Sun and our satellite, the latter tra-
verses the cone of shadow that the Earth projects far behind
it. For this phenomenon to occur, the Moon must, either at
the moment of opposition or full moon, be in the plane of
the ecliptic or very near it, that is to say, in or about the
nodes.
If the Moon’s orbit was parallel to the ecliptic, that is to
say to the curve which the Earth describes round tlie Sun in
the course of a twelvemonth, there would be a completeTHE ECLIPSES.
205
eclipse whenever the Moon was full, but as the lunar orbit
is inclined rather more than 5 degrees to the plane of the
* ecliptic, the Moon is sometimes above and sometimes below
that plane. It may, therefore, happen that, when full, it
will pass quite beyond the Earth’s shadow, or merely graze
it with its edge (this is termed appulse), or there may be a
partial eclipse, which means that the Moon traverses part of
the shadow. The eclipse is total when, at the moment of
the opposition, the Moon is in the node itself, and is con-
sequently plunged altogether into the shadow. The eclipse
is central when the centre of the Moon coincides with the
axis of the cone of the shadow.
During an eclipse the Moon’s disc is successively deprived
of the light from the various parts of the solar disc; thus
its brightness diminishes gradually, and is only extinguished
when the disc is completely buried in the terrestrial
shadow.
As the Moon is not luminous of itself, and only shines
when it is illuminated by the Sun, it follows that whenever,
in its circular motion round the Earth, it is in a position
where the Sun’s light cannot reach it, it must disappear
from view or become eclipsed.
As the Earth is an opaque body, it projects opposite to
the Sun a cone of shadow which the light of this luminary
cannot penetrate. The top of this cone extends to an im-
mense distance—three times that of the Earth from the
Moon. The eclipse of the Moon is visible throughout all
the terrestrial hemisphere turned towards it.
The penumbra is the subdued light witnessed during the
gradual diminution.
There are never more than seven ecKpses in a year, and
never less than two. Wlien^ there otq only two, they areASTRONOMY.
206
always eclipses of the Sun. The eclipses of the Moon are
less frequent than those of the Sun, and sometimes there is
Fig. 45.—Eclipse of the Moon.
not a single one during the year, as in 1768, 1767,1788,
1789.
II.
The solar eclipses are produced hy the interposition of
the Moon between the Sun and the Earth, when the Moon
is new, that is to say, when it is in conjunction with the
Sun.
The solar disc is contracted upon one side, and the oh-THE ECLIPSES.	207
scure part increases in volume, gradually diminishes, and
then resumes its normal appearance.
Sometimes the obscurity, extends to the whole disc* and
the Sun disappears altogether; sometimes, too, there is a
large spot projected upon the Sun, with a luminous ring.
It is worthy of notice that solar eclipses only occur at the
epoch of new moon or conjunction, while lunar eclipses
only take place at the epoch of full moon or opposition.
The distance of the Moon from the Earth is so relatively
small that its apparent diameter, incomparably smaller than
that of the Sun, seems to us quite as large and sometimes
even larger.
When the Moon in its conjunctions is so near its nodes as
to be almost in the plane of the ecliptic, the cone of shadow
which it projects reaches the Earth, first touches it at a certain
point, then traverses and finally leaves it after a certain in-
terval of time. Thus, those parts of the Earth comprised
within the space traversed by the lunar shadow see the
eclipse of the Sun in succession.
The solar eclipses are partial, total, or central; partial
when the Moon only conceals a part of its solar disc; total
when the whole disc is hidden (and it is worthy of note that
the same eclipse may be partial in one place and total in
another); central when the spot from which they are ob-
served is the centre of the shadow, on the straight line
which joins the centres of the Sun and the Moon.
In the annular eclipses, the solar disc entirely overlaps
that of the Moon, and has the appearance of a luminous
ring.
When the discs of the Moon and the Sun merely touch
during their passage, there is an appulse as it is termed.
The size of partial eclipses is generally calculated byASTRONOMY,
208
taking as a measure of the eclipsed part twelfths of the
diameter of the eclipsed body; these have received the
name of digits, and they are subdivided into 60 minutes.
Fig. 46.—Eclipse of the Sun,
The moment of immersion is when the edge of the Moon
commences to encroach upon that of the Sun, or of any
other body which it is about to eclipse. Emersion is when
the last portions of the Moon move clear of the body which
has been eclipsed by it.
In a lunar eclipse, immersion is the moment when the
luminous part of the Moon enters the cone of shadow,
emersion when it emerges from the cone.THE ECLIPSES.
209
III.
During total eclipses of the Sun, the Moon is surrounded
by a luminous corona, which seems to be of a silvery hue.
This colour was very brilliant during the eclipse of July,
1842, being composed of a circular zone contiguous to the
Moon’s edge, and of a second zone, less bright, bordering
upon the first. The light of this second zone became
weaker from the inner to the outer part, while that of the
first was about uniform.
When the sky is very clear, the corona has an extent
equal to the diameter of the Moon, but it is only brilliant
within far narrower limits. The corona often emits rays or
tufts of considerable length, and, taken altogether, is the
most remarkable phenomenon of the eclipse visible to the
naked eye.
Under the same circumstances, reddish protuberances
are to be seen at various points of the Moon’s surface, and
they are generally classified as prominences, protuberances,
flames, clouds, and mountains. The result of M. Cleiy’s
observations at Gothenburg showed that the protuberances
on the western edge became more salient after the eclipse
began; that a protuberance, invisible at the commencement
of the eclipse, took form as the eclipse progressed, whereas
the easterly protuberances contracted and finally disap-
peared. M. Arago holds that these protuberances are
neither mountains nor apparitions caused by a deviation of
the solar rays in the uneven surface of the Moon’s edges,
but that they are to be explained by the hypothesis of
clouds floating in the diaphanous atmosphere which sur-
rounds the photosphere of the Sun.
During the eclipse of July 8th, 1842, the attention of210
ASTRONOMY.
astronomers was attracted by these protuberances or pro-
minences, which are visible during total eclipses of the
3un, and which dart around the Moon like gigantic flames,
of a rose or peach coloured tint.
Father Secchi concludes that the prominences are masses
of luminous matter, possessing great vivacity and powerful
photogenic action; that there is a mass of protuberance-
producing matter suspended isolated, like clouds, in the
atmosphere, and that there is a zone of this matter entirely
surrounding the Sun. The prominences, according to him,
are produced by this stratum, and rise above the general
surface, from which they even become detached at times.
Some of them resemble the smoke which issues from a
chimney, or the crater of a volcano, and which, when it
peaches a certain height, is influenced by a current of air
and takes a horizontal direction. The number of pro-
tuberances is incalculable, they being at times so numerous
that it is impossible to count them, and they also vary
very much in altitude. Some have been remarked with an
altitude three, six, and even ten times that of the earth’s
diameter; but, as a general rule, they are from three to six
times its diameter. M. Janssen having succeeded in study-
ing the protuberances by spectrum analysis, ascertained
that hydrogen is the main element in their composition,
and his observations have been confirmed by subsequent
experiments.
IV.
Amongst the most remarkable solar eclipses in France
was the annular eclipse of 1764, visible at several places,
and lasting 5 hours, 29 minutes, 30 seconds. A similarTHE ECLIPSES.
211
eclipse was observed at Paris on the 9th of October, 1847.
But the finest eclipse of the present century, so far as Paris
was concerned, took place on the 15th of March, 1858,
beginning at 11*21 a.m. It was at its culminating point at
1*11 p.m., and terminated at 2*28 p.m. This eclipse was
eagerly looked forward to, as an opportunity for trying new
instruments and making fresh experiments. The aspect of
the sky was not very favourable for the purpose, but still
many useful observations were taken. Fig. 47 represents
several photographs taken by M. Porro, director of the
Technomathical Observatory, and M. Quinet, of the phases
of this eclipse.
The eclipse of August 18th, 1868, was visible in Eastern
Africa, upon the shores of the Bed Sea, in Arabia, China,
Madagascar, Ceylon, and Australia.
The Moon was emerging from a perigee unusually near
to the Earth, and passing through the upper node of its
orbit. Hence it followed that the Sun at its eclipse was
very close to the zenith in those countries where the
eclipse occurred at noon. Consequent^, the diameter of
the Moon was very large, and the motion of the shadow
extremely slow.
The maximum duration of the total eclipse was in the
Gulf of Siam, where it lasted 6 min. 50 sec., the Sim being
only 2£ degrees from the zenith. The total eclipse of 1868
was one of the greatest that ever took place. Never, in the
memory of man, had an eclipse lasted so long, and only
two were to be compared to it in point of size—1'these were
the Thales eclipse, upon the 28th of May, 585 b.c., and that
observed in Scotland on .the 17th of July, 1843, which was
long spoken of as the Black Hour. Those who went to India,
M. Janssen amongst others, to witness the eclipse of 1868,213
ASTRONOMY.
were rewarded for their journey, as immediately after the
total eclipse two magnificent protuberances appeared, and,
on examining their light through the spectroscope, they
Fig. 47.—Eclipse of the Sun, March 15th, 1858.
Nos. 1, 2, 3. Crescent phases.—No. 4. Maximum phase.—Nos. 5, 6, 7. Waning
phases.—No. 8. The spots observed on the Sun a week after the eclipse.
t In Nos. 3, 4, 5, the edge of the Moon is seen protruding beyond the Sun.
were found to be composed of two immense gaseous and
incandescent columns, in which the element of hydrogen
was predominant.
But the most valuable discovery resulting from these
observations was the method, hit upon by M. Janssen at
the very moment of the eclipse, by which the protuberancesTHE ECLIPSES.
213
and circumsolar regions might be studied at any time.
This method is based upon the spectrum properties of the
light of the protuberances—a light which resolves itself
into a small number of very luminous beams, correspond-
ing to the obscure beams of the solar spectrum. In the
interval between the 19th of August and the 4th of Sep-
tember M. Janssen collected a large number of facts
bearing upon this subject. But the original conception of
this method belongs not to him, but to Mr. Norman
Lockyer who, having first lighted upon it in 1866, was
working it out in London at the very time that M. Janssen
was engaged upon the same study at Guntor in India.
y.
The general phenomena of a total eclipse have been thus
graphically described by Father Secclii. “ The really inte-
resting features of an eclipse do not begin until the centre
of the Sun is covered by the Moon. The light then
diminishes very perceptibly, and as the moment of the
total eclipse approaches, the decrease is so rapid, that it
almost creates a feeling of terror. What is most striking is
not so much the diminution of light as the change in colour
of the surrounding objects—everything assumes a sombre
and gloomy hue. The bright green of the meadows becomes
grey, and the highest regions of the sky near the Sun have
a leaden colour, while near the horizon the sky is a sort of
yellow-green. The human face takes a cadaverous colour,
like that produced by the flame of alcohol steeped in
chlorure of sodium. This yellow tint, coupled with the
decline in temperature, seem to indicate a diminution of the
vital forces of nature.214
ASTftONOMY.
“ Accompanying this, there is a general silence in the
atmosphere. The small birds seek shelter, the insects dis-
appear, and everything seems to indicate a coming catas-
trophe. As Mr. Forbes remarks, it is easy to understand
how uneducated people are struck with terror at such a
spectacle, and look upon it as the forerunner of everlasting
darkness. Father Faura tells us that, during the last
eclipse, in 1868, vast numbers of the Chinese took refuge
upon their junks, to escape a disaster which, notwithstand-
ing the presence of astronomers with their instruments of
observation they could not be persuaded was imaginary.”*
It is easy to follow the progress of the total eclipse. The
crescent wanes with astonishing rapidity, and is soon
reduced to a thin thread, terminating in almost imper-
ceptible points, which in their turn vanish. Then the scene
undergoes a sudden and complete change, and a very black
disc, surrounded by a magnificent gloria of silver rays, with
jets of rose-coloured flames glittering amongst them, stands
out against a leaden sky. This spectacle, at once beautiful
and portentous, is well described by Baily, who says:—
“ I was engaged in counting the oscillations of my chrono-
meter, in order to fix the exact moment of the total disap-
pearance, while a vast crowd filled the streets, to witness
the phenomenon offered to their admiring gaze. Suddenly,
as the last ray disappeared, a loud shout went up from the
immense multitude. An electric thrill went through me,
and, looking upwards, I saw the most beautiful spectacle
which the imagination can conceive. The great orb of day
was replaced by a disc as black as pitch, surrounded by a
brilliant gloria, such as we see in pictures around the head
of a saint.
* Father Secchi on The Sun, p. 144.THE ECLIPSES.
215
“ Lost in astonishment, I wasted a few of the precious
moments, and almost forgot the object of my journey.
From the descriptions which I had previously read, I was
Fig. 48.—The aspect of the Sun in eclipse.
quite prepared to see a certain amount of light around the
Sun, but I expected it to be faint and dim, whereas my eyes
beheld a splendid aureole, the brilliancy of which, very
accentuated upon the edge of the disc, gradually faded away
to nothing at a distance about equal to the diameter of the
Moon. I had not reckoned upon anything of this kind.
“ Mastering my surprise, I again looked through my
telescope, having first taken out the black glass inside it.216
ASTRONOMY.
Here a new surprise awaited me. The corona of rays
around the lunar disc was broken at three points by immense
purple flames with a diameter of two minutes. They
appeared to be perfectly steady, and presented an aspect like
the snow-covered summits of the Alps during sunset. I
could not discern whether these flames were clouds or
mountains, for, while I was studying them, a ray of sun
shone through the darkness and prevented me from carrying
my examination any further.”
VI.
History contains some curious accounts, many of them,
no doubt, exaggerated, as to the obscurity which reigns
during a total eclipse of the Sun. During that of 1560, the
darkness was so intense that people could not see their
hand before them. The Agathocles eclipse, which took
place in the year 310 b.c., is said to have created so great
an obscurity that the stars appeared in every quarter of the
sky.
During the eclipse of 1715, Halley saw Venus, Mercury,
Capella, and Aldebaran. In another direction, where the
atmosphere appeared still darker, he counted twenty-two
stars.
During this same eclipse, which took place at 9 a.m.,
Louville states that it was too dark to read more than a few
words here and there.
During most other eclipses, also, observers have been
able to distinguish many of the planets and constellations.
It is narrated by eye-witnesses of the eclipse of 1706, that
at Montpellier, the bats were flying about, that the fowls
and pigeons went to roost, that the caged birds ceasedTHE ECLIPSES.
217
singing and put their heads under their wings, and that the
very beasts of burden stopped while at work.
Professor de Lentheric, speaking of the eclipse of 1842
at the same place, says that “ the bats, thinking night had
set in, left their hiding-places; an owl flew over the town,
the swallows disappeared, the fowls went to roost, and some
oxen that were passing by St. Maguedelonne church drew
up in a circle back to back, as if they were expecting to be
attacked.”
Abbe Deytal adds that “ some horses which were driving
a threshing-machine were seen to lie down; the sheep
scattered over the meadows flocked together as if in fear;
the chickens took refuge under their mother’s wing; a
pigeon, overtaken in his flight by the obscurity, flew against
a wall and, dropping to the ground, did not rise again until
the Sun had reappeared.”
Arago, alluding to an incident which occurred during the
same eclipse, says that an inhabitant of Perpignan, keeping
his dog without food on the previous evening, gave him some
meat just as the total eclipse was taking place. The animal,
which had begun to devour it with great avidity, let it fall
from his mouth when the obscurity became complete, and
would not touch it until the Sun shone forth again. At
La Tour, a town in the Eastern Pyrenees, an inhabitant
kept three linnets. Early on the morning of July 8th, 1842,
he hung their cage from his window, but though they all
seemed in perfect health, one of them died during the
eclipse.
Biccioli relates that during the total eclipse in 1415,
several birds were seen to drop dead from fright in Bohemia.
The same is reported of the eclipse of 1560; and Arago says
that during the eclipse of 1842 the fowls which were being218
ASTRONOMY.
fed left the grain and took shelter in a shed, one of the hens
covering the chickens under her wing.
It has also been noticed that ants will come to a halt when
the Sun is totally obscured, but they do not drop the
burdens they are carrying, and continue their journey when
the light reappears.
It is also said that some bees which had dispersed from
their hive at sunrise, flew back to it at the moment of the
total eclipse, and remained there until it was over.
One singular phenomenon, attested by several credible
witnesses, is the change which takes place in the colour of
terrestrial objects when the obscurity of solar eclipses has
reached a certain point. Plantade and Clapes, in their
account of the total eclipse at Montpellier on the 12th of
May, 1706, relate that objects change in colour according
as the eclipse progresses or declines. At the eighth digit,
that is to say when two-thirds of the Sun’s diameter were
hidden by the Moon, both before and after the total
obscurity, they were of an orange-yellow tint. When the
eclipse had attained rather more than eleven digits, that is
to say when only ^ of the Sun’s diameter was visible, they
seemed to be of the colour of running water.
Halley, speaking of the total eclipse in 1715, says:
“ When the eclipse had reached ten digits, that is to say
when the Moon covered five-sixths of the sun’s diameter, the
aspect and colour of the sky began to change, the azure blue
turning into a sort of livid purple.”
These changes of colour, which are merely due to an
effect of the law of optics, have been remarked by all
succeeding astronomers.THE ECLIPSES.
219
vn.
All lunar and solar eclipses reappear in the same order,
after an interval of about 18 years and 11 da}rs, which are
termed the cycle of Meton, or the golclen number. The
Chaldseans called this period saros. Thus, at the expiration
of eighteen solar years, the Sun reappears, either in oppo-
sition or conjunction, at the same distance from the nodes of
the Moon’s orbit as it was at the commencement of this
period.
It suffices therefore to have observed the eclipses during a
period of eighteen years to be able to predict those which
will recur during any interval of the same duration.
Koemer, to whose researches we owe the discovery of the
velocity of light, invented a sort of planisphere, or watch,
which, by the turning of a fly-wheel, indicates all the past
and future eclipses of the planets. This and other curious
mechanical contrivances are to be seen in the Paris observatory.
M. de la Hire also invented a machine which indicates the
eclipses past and to come, according to the mean motion of
the Moon, together with the points of lunation and the
epacts.
The astronomical epacts enable us to predict the eclipses
with great exactitude, by calculating the mean conjunctions,
or new moons, as well as the mean oppositions, or full
moons, then determining for those periods the distance of
the Sun from the node of the Moon at those periods, and
finally ascertaining if this distance comes within the limits
where an eclipse would occur.
As M. Delaunay points out, “ the ancients, who had not
nearly so precise a knowledge of the Moon’s motions as we
have, were unable to predict the eclipses of the Sun. They220
ASTRONOMY.
could only foretell those of the Moon, their forecast being
based on the periodical recurrence of eclipses presenting the
same character, and with the same intervals between them
every 18 years 11 days. Thus, after observing and keeping
a record of all the lunar eclipses which occurred within that
period of time, it was easy to predict the order of the eclipses
which would take place in a corresponding period. At the
present day, with our extended knowledge of the motions
both of the Sun and the Moon, we are able to calculate for
years, even centuries beforehand, not only the general
circumstances of lunar and solar eclipses, but the peculiarities
which they will manifest at any given spot upon the earth.
We can even form a retrospective estimate of the appearance
presented in different localities by an eclipse that took place
hundreds of years ago.* ”
Thus eclipses are useful in chronology, either to fix the
precise date of a remote occurrence or to correct misleading
indications.
Herodotus, in his first book, says: “After that, the
Lydians and the Medes were at war for five consecutive
j^ears, and the fortunes of the contending armies varied;
and while the struggle continued to favour first one side
and then the other, it happened that in the sixth year, just
as a battle was being fought, the day suddenly changed into
night. Thales of Miletus had foretold this phenomenon to
the Ionians, indicating the very year during which it actually
occurred. The Lydians and Medes, seeing that night had
suddenly taken the place of clay, ceased their warfare and
concluded peace.”
This eclipse is known as the Thales eclipse. The various
authors who have spoken of it assign very various dates,
* Annual report of the Bureau dcs Longitudes, Delaunay, p. 427, 1868.THE ECLIPSES.
2ZL
ranging between 626 and 583 b.c., but Airey, basing his
induction upon the most recent data as to the Moon’s
motions, fixes it on the 28tli of May, 585 b.c. Diodorus
Siculus also relates some curious details concerning a total
eclipse of the Sun which took place whilst Agathocles,
flying from Syracuse before the Carthaginians, was on his
way to Africa. “Agathocles, though surrounded by the
enemy, made an unexpected escape. Upon the following
day there occurred so complete an eclipse of the Sun that
one might have supposed that night had set in, for the
stars appeared all over the heavens. And the soldiers of
Agathocles, thinking this presaged the displeasure of the
gods, were in great fear.” *
Astronomers have ascertained that this eclipse must have
occurred in the year 310 b.c.
VIII.
Until astronomy revealed the causes of an eclipse, that
phenomenon, like the comets or the Aurora Borealis, was a
source of terror to many, and of wonder to all.
One of the most remarkable facts relating to this subject
is the use to which Christopher Columbus turned his know-
ledge of these phenomena at an extremity when he and his
fellow-travellers were threatened with starvation. Com-
pelled to have recourse to the natives of the New World for
subsistence, he treated them with great kindness. But in
the course of time the supply of provisions began to fall
short, and the natives exhibited a reluctance to renew them.
In this extremity he happened to recollect that a lunar
eclipse was at hand, so he assembled all the neighbouring
* Diodorus, Book xx. § 5.22a
ASTRONOMY.
chiefs, informing them that he had an important communi-
cation to make concerning the preservation of their life.
When they had met, he reproached them with their want of
friendliness, assuring them that God, who had him under
his protection, would soon punish them. He went on to
say: “ Have you not seen how I have punished any of my
soldiers who have disobeyed me? You will soon be a yet
more striking instance of the vengeance wrought by the God
of the Spaniards, and as a warning of what is to come, you
will this evening see the Moon grow red, and then withdraw
its light from you. But this is only the prelude of the mis-
fortunes which will overwhelm you if you refuse to give me
food.”
The eclipse began a few hours afterwards, and the natives
were nearly mad with terror, throwing themselves at Co-
lumbus’ feet, and imploring pity. He, in order to make his
influence over them stronger, pretended to comply with
their demand, and retired to an inner chamber, professedly
to appease the wrath of the divinity. The natives continued
to utter loud cries of alarm, and when the Moon reappeared
Columbus told them that the divinity had promised to
pardon them on the condition of their supplying him with
all he required, and ever afterwards they kept their word.
Fontenelle, in his work Entretiem sur la Plurality des
Mondes, says: “ Throughout the East Indies it is believed
that the eclipses of the Sun and Moon are caused by a
dragon with large black claws, which he stretches out to
seize those two luminaries, and that is why the Indians are
seen plunged up to their necks in water at these periods;
for in the Hindoo religion such an attitude is looked upon
as favouring the Sun and the Moon in their combat against
the dragon. In America it was thought that when the Sun*
Fig. 49.—Christopher Columbus and the eclipse of the Moon.m
ASTKONOMY.
and Moon were in eclipse, they were offended, and various
devices were resorted to for propitiating them. But the
Greeks, civilised as they were, believed that the Moon was
bewitched, and that the magicians compelled it to come
down from the sky, and deposit a venomous scum upon the
grass. And even during the total eclipse of 1654, many
people took refuge in their cellars.”
IX.
The following fact shows what a great effect eclipses had
upon the ancients.
Pelopidas, the Greek general, was about to engage in
battle against Alexander of Pheree (846 b.c.), when “just
as all was ready for the general's departure an eclipse of the
Sun took place, and the town was plunged in darkness.
Pelopidas, finding that this phenomenon had so‘alarmed his
soldiers as to render them incapable of sustaining the com-
bat, started on his expedition, accompanied only by three
hundred volunteers, in opposition to the soothsayers and
the rest of his fellow-citizens, who looked upon this eclipse
as the sign of misfortune to some important personage.”*
In the Peloponnesian war, Pelopidas had equipped 150
vessels, and just as all the troops had embarked, and
Pericles had taken his place in the trireme, an eclipse of
the Sun came on. “ The men, alarmed by the sudden ob-
scurity, saw in it a presage of disaster. Pericles, finding
that the pilot had lost all control over himself and his vessel,
threw his mantle oyer his head, and asked him whether he
saw anything alarming in that. The pilot replying in the
negative, Pericles told him that the only difference between
* Plutarch's Life of Pelopidas,THE ECLIPSES.
225
the causes of obscurity was that the Sun was larger than
his mantle.”*
Drusus, sent by Tiberius to quell the revolt amongst the
Roman legions, took advantage of the terror inspired by a
lunar eclipse to restore order. Tacitus, referring to this
occurrence, says: “ Matters looked very threatening that
night, but a happy accident re-established order. The
Moon, which was shining in a clear sky, suddenly grew
dim. The soldiers, unacquainted with the cause of this phe-
nomenon, imagined it to have some bearing upon their own
position, thinking that the eclipse of the Moon was meant
to represent their own sufferings, and that if it regained its
normal brilliancy, they would attain the object of their de-
sires. . Then they began to sound their clarions and
trumpets, their spirits being elevated or depressed accord-
ing as the Moon became brighter or more obscure; and
when the mass of clouds at last concealed it from their
eyes, they thought that it had disappeared for ever, and, as
the transition from terror to superstition is an easy one>
they inferred that the gods were angry with them for ‘ rebel-
ling/’ f Tacitus then goes on to describe how Drusus took
advantage of their fears.
The appended story, somewhat analogous to that of
Christopher Columbus, described above, will also serve to
show the light in which two ancient nations envisaged these
phenomena.
Plutarch, in his Life of Paulus Emilius, says that on
the eve of a great battle with the Lacedaemonians, “ the
Moon, which was shining brightly in the sky, suddenly be-
gan to grow dim, and, after undergoing several variations of
* Plutarch’s Life of Pericles.
t The Annals of Tacitus, book i.
Qm
ASTRONOMY,
colour, became altogether eclipsed. The Roman soldiers
begftn to beat upon the brazen vessels, as is their habit on
such occasions, in order to call back the light, elevating, at
the same time, torches and firebrands towards the sky.
The Lacedaemonians, on the contrary, were struck with
terror, and a loud cry went through their camp that the
phenomenon heralded the downfall of their king, Paulus
Emilius,. though he was not altogether unacquainted with
the natural causes of an eclipse, obedient to the customs of
his religion, sacrificed eleven young bulls when the Moon
shone forth again. At daybreak he immolated twenty oxen
to Hercules, without, however, obtaining any propitious
signs; but when the twenty-first ox was slain, the signs
appeared, announcing that he would be victorious if he
remained on the defensive,”
X.
. Nicias, the Athenian general, and his soldiers, alarmed
by an eclipse of the Moon, were surprised by the Syracusans
in Sicily, his army defeated, and himself taken prisoner and
put to death.
Pl.utarch, in his Life of Nicias, pens the following remark-
able passage: " Anaxagoras, who was. the first to write an
account of the phases of light and shadow observed in the
Mopn, was not at the time a well-known author, and his
treatise, far from being generally circulated, was kept a pro-
found secret, and only confided to a very few persons, who
did. not place much reliance upon its contents. Moreover,
natural philosophers, and meteorolesci,. as they were then
called, were held in great abhorrence, for it was said that
they degraded the divinities by reducing their influence toTHE ECLIPSES.
227
capricious causes, unregulated forces, and necessary pas-
sions. Thus it was that Protagoras was exiled, Anaxagoras
cast into prison, and with difficulty saved from death by
Pericles; and Socrates, though he had nothing in common
with their doctrines, put to death because he was a philo-
sopher. It was not until much later that the doctrines of
Plato enlightened his fellow-citizens, and, aided by the life
of its expounder, as by his submission to the physical
causes involved in the principles of divinity and sovereignty,
put an end to the calumnies which were heaped on phi-
losophy. His doctrines, foo, brought about the study of
mathematics. This is the reason why his friend Dion, who
noticed an eclipse of the Moon just as he was about to start
from Zacynthus to attack Dionysius, was not deterred from
setting sail, and continued his voyage to Syracuse.”
It- is very evident that the more the works of nature are
studied, the greater must be our admiration of the wisdom
of their Creator. The Almighty has effected his purpose
with the most simple means, as we see the more clearly
the further we advance in science, the study of which, so
far from having a tendency towards impiety, must rather
animate us with the sentiments of Plutarch, who, though he
had no conception of the great physical and moral truths
now within human ken, exclaims:
“ Man enlightened by the study of Nature’s laws cannot
but be inspired towards the Divinity with a feeling of venera-
tion, full of security and hope, instead of a, superstitious
and timid devotion.” *
* Plutarch’s Life of Perides, p. 207.CHAPTER X.
I
THE TIDES.
Their nature—The first of the Greeks who inquired into the causes of this
phenomenon—Passage from Lucanus—Influence of the Moon and the Sun
upon the waters—Theory of tides—M. Delaunay on the tides—Solar and
lunar tides—Obstacles to tides—Height of tides in the Moon—Flood*
bar or “ bore ”—M. Babinet's description—Utility of tides—A charming
allegory.
L
Tide (maree) is derived from the Latin mare (sea). It is
the alternating and daily motion of the ocean covering and
receding from the shore. In the course of 24 hours
49 minutes its waters twice flow to and recede from the
equator towards the poles, and from the poles towards the
equator.
The sea rises for about six hours, covering the shore, and
forcing its way up the mouth of the rivers. The waters,
after attaining their extreme height, remain a short time
(about a quarter of an hour) unchanged, and then gradually
recede. This retreating motion also lasts about six hours,
when they reach their lowest depression, when, after a
quarter of an hour’s repose, they again begin to rise.
The flood, which is also called high tide, is the motion of'
the waters towards the poles; the ebb, also called loio tide,
is the return of the waters towards the equator.
II.
The first of the Greeks who directed attention to theTHE TIDES,
229
causes of the tide was Pytheas of Marseilles, who lived .about
320 b.c. He asserted that the full Moon produced the flood,
and the waning Moon the ebb ; but, though it is true that
tides are attributable to lunar influence, he was very far
from the truth. Newton first demonstrated the relation of
tides to the other phenomena of universal gravity.
Lucanus, alluding in the Pharsalia to the French coasts,
thus speaks of the tidal phenomena:—“ There is the same
gladness upon this shore, for the possession of which earth!
and water seem to be disputing, as it is in turn abandoned
and inundated by the ocean. Is it the ocean itself which
rolls its waves from the extremity of the axis, and then
draws them back to it ? Is it the periodical return of the
luminary of night which drives them before it ? Is it the
Sun which attracts them to feed its flames, which, pumping
up the sea, raises it towards the sky ? Let those who seek
to study the working of creation sound this mystery. For
my part, as the gods have concealed from me the mighty
cause of this great motion, I do not seek to fathom it.” *
Newton and Laplace, to use M. Babinet’s expression,
sought, and, to the great honour of the human race, found.
As the Moon successively passes above each point of the
ocean, it, by virtue of the laws of attraction, draws towards
it the waters, which are of extreme mobility.
III.
It has been ascertained :—
1st. That the waters of the ocean rise in succession at
each point over which the Moon passes ;
2nd. That the Mediterranean has no other tide than that
'* Lucaims, The Pharsaliat book ii.ASTRONOMY.
230
imparted to it by the ocean through the Straits of Gibraltar,
the reason being that the Moon never passes over it perpen-
dicularly ;
3rd. That the ebb and flood undergo, like the Moon, a
retardation of three-quarters of an hour every day;
4th. That the tides only recur at the same hour once in
every thirty days, which is precisely the interval between
two new moons;
5tli. That the tides are always highest when the Moon is
at its nearest point to the Earth ;
6th. That the tides are highest at the time of full and new
moon,, because at that time the waters are more strongly
attracted, owing to the attraction of the Sun being concur-
rent'with that of the Moon; whereas at the epoch of the
quadratures and quarters the tides are less, because the Sun
neutralises about a third of the Moon’s attraction.
IV.
When the Moon is perpendicular over a particular point
of the ocean, the waters there, attracted by the orb of night,
begin to rise, and, as this attraction acts in a contrary
direction to that of the Earth, the waters upon each side of
the globe, exposed to an oblique action from the Moon,
augment in weight, and tend more towards the centre of the
Earth. At the same, time, those parts of the sea diametri-
cally opposed to the point attracted by the Moon, being
less attracted by that luminary than the centre of the Earth,
because they are farther away, do not tend so much towards
the Moon as-the centre of the Earth, by which means the
sea rises on the side opposed to the Moon, and the ocean
presents the phenomenon of tides in two opposite hemi-
spheres.THE TIDES,
231
Pig. 50.—The phenomena of tides.232
ASTRONOMY.
The attractive force exercised by the Sun upon the Earth,
though only a third of that of the Moon, suffices to cause
an ebb and flow.
Thus there may be said to be two separate sorts of tide:
the solar and the lunar.
The Sun causes a rise in the sea at noon and midnight,
the hours of its passage across the meridian, and produces
a fall at ten in the morning and ten in the evening.
Twice a month, at the syzigies, these two tides concur in
direction, and combine into one, because at that time the
Sun attracts the waters in the same direction as the Moon,
and produces a corresponding effect; whereas at the quad-
ratures, as I have already said, the Sun, being perpendicular
to the Moon, has an action contrary to that of the latter.
Hence it is that the tides are least during the first and last
quarters, greatest at the full and new Moon.
y.
M. Delaunay writes as follows concerning the theory of
tides:	’
“ If the Earth was altogether a solid body, it would give
as a whole under the attraction which the Moon exercises
upon its various parts, without undergoing the least altera-
tion in shape. But the Earth is not altogether solid. Part
of its surface is covered by the waters of the ocean, which,
by reason of their fluidity, are easily moved by the forces
which act directly upon them. Now, the various portions
of these waters, spreading all around the terrestrial globe,
and, consequently, placed at unequal distances from the
Moon, are not equally attracted by it. In that region of
the globe’s surface which is turned towards the Moon, theTHE TIDES.
233
waters of the sea are more powerfully attracted than the
solid portion of the Earth, taking it as a whole; in the oppo-
site region, on the other hand, the sea waters are less
attracted than the solid part. It results from this that the
waters situated on the side facing the Moon are made to
tend towards it by this excess of attraction, and that on the
opposite side of the Earth the waters tend to recede rela-
tively to the mass of the globe which is more strongly
attracted than they are. The consequence is, that the
waters accumulate together on the side where the Moon
appears, forming a prominence there which would not exist
but for it, while just in the same way they accumulate and
form a prominence upon the side opposed to the Moon.
Added to this, the Earth, by virtue of its rotatory motion
upon itself, brings the various parts of its surface perpendi-
cular to the Moon, so that the two liquid prominences in
question, while always occupying the same position in
respect to the Moon, are continually changing their place
upon the surface of the Earth; and it will be found that at
the same point on this surface, in the same part, two high
tides will be observed in succession—and consequently two
low tides—while the Earth is making a total revolution
relatively to the Moon, that is to say, in the course of
24 hours 49 minutes.
“ The Sun produces an analogous effect upon the waters
of the sea, but the enormous mass of the solar body is more
than counteracted by its great distance from the Earth; so
that, as a matter of fact, the tide caused by the action of
the Sun is not comparable to that due to the action of the
Moon. The phenomenon, therefore, in its main features,
is dependent upon the position of the Moon in respect to
the Earth; the action of the Sun merely modifies it, either234
ASTRONOMY.
by advancing or retarding the hour of high-tide, either by
augmenting or diminishing its intensity, according to the
position which the Sun occupies in the sky as regards the
Moon.”*
VI.
The highest point of the tide is never exactly underneath
the Moon, but a short distance, at no time exceeding 15
degrees, to the eastward.
The waters of the ocean, being very inert, do not yield
immediately to the attraction which the Moon exercises
upon them, and this is why they do not attain their highest
elevation at the moment when the lunar attraction is
greatest, but a short time afterwards.
Not only does the solar attraction impede that of the
Moon, but the resistance and oscillation of the waters, the
friction of the coasts, and their irregular shape, are all so
many obstacles which retard the high tide. At the Cape of
Good Hope, for instance, there is a retardation of two hours
and a half, but at Dunkirk and Dover it is twelve hours,
that time being taken by the ocean to traverse the English
Channel and the Straits of Dover, and to force itself along
the coasts. But the flood and the ebb are, notwithstanding,
quite regular in their recurrence.
VII.
The maximum and minimum of elevation in the ocean
depends not only upon attraction, but also upon the bed of
the sea and the coast-line. It is easy to understand that
* Delaunay’s Annuary for 1868, p. 467.THE TIDES.
335
the tide will be higher in a narrow channel, where the
waters are forced together, than upon a wide and open shore.
At St. Malo, in the English Channel, the tides are some-
times 50 or 60 feet; in the north of the Bay of Biscay, and
at Brest, they rarely exceed 23 or 28 feet; at St. Helena
they are never more than four feet. At the Island of
Eoumon, and other points of the great Southern Ocean,
the height of the tides is hut 18 inches.
It has been noticed that at the mouth of the Garonne, the
flood lasts seven hours, and the ebb only five, and this dif-
ference is attributed to the course of the stream, the current
of which runs down in a contrary direction to the flood, and
consequently quickens the ebb.
The wind has also a certain influence upon this pheno-
menon. If it is blowing strongly in the direction of the tide,
the waters rise higher than during calm weather; but if the
wind is blowing in the opposite direction, the tide is lower.
The tide varies in height from day to day, even upon the
same coast. It augments for a week, and then diminishes
during the same lapse of time, so that, twice in every month,
there are two high tides at an interval of a fortnight, and
two low tides at the same interval; while twice a year, at
the spring and autumn equinoxes, there are two tides much
higher than at any other period.
Newton calculated that if there are seas in the Moon, the
attraction of the Earth must cause the tides there to be
more than 100 feet high, whereas the general average of
the Moon’s attraction does not raise the waters of our globe
to a height of more than 15 feet.236
ASTRONOMY.
VIII.
The coasts and the basin of the Seine present a curious
tidal feature near Quillebceuf; it is termed, during the full
and new Moons of the equinoxes, the floocl-bar, or “ bore,”
and has been well described by the late M. Babinet, who
says:
“ This extraordinary motion of the sea-waters, immense
in its development, and capricious in its action, owing to
the influence of localities, winds, and the variable state of
the bed of the stream, has formed the subject of long
researches, the result of which I now lay before you. The
first point to be considered is the meaning of the word.
Whereas, as a general rule, and even at the extreme mouth
of the Seine itself, as at Le Havre, Honfleur, and Berville,
the sea, at the commencement of the flood, rises gradually
and almost imperceptibly, in that part of the stream above
and below Quillebceuf it precipitates itself in an immense
cataract, forming a sort of rolling wave, which extends right
across the river to a distance of six or seven miles, and
instantaneously fills the vast basin of the Seine.
“ This great wave, after dashing itself against the quays of
Quillebceuf, runs up the narrow bed of the stream, which at
that point remounts towards its source faster than a race-
horse can gallop. The vessels, drifted about, are, to use a
local expression, en perdition. The bed of the stream
undergoes a displacement of several miles from the
one to the other of the cliffs, which overhang it, and the
sand and mud banks in the bottom are agitated like the
waves upon the surface. Nothing can be more remarkable
than these ‘ bores,’ seen on a calm and bright day, without
any such apparent cause as wind or thunderstorm.THE TIDES.
237
“ These great crises of Nature, brought about by that
eminently silent cause universal attraction, are announced
and accompanied by the most deafening noises. Homer, the
great painter of Nature, would seem to have witnessed some
such phenomena when he says: ‘ So at the mouths of a
river whose course is directed by Jupiter, the immense wave
roars against the current, while the precipitous shores re-
echo afar the noise of the sea, which the river is repelling
from its bed.’ ”
A great advantage of the flood-tide is that it forces the
sea-water up the rivers, and makes their beds deep enough
to admit ships of heavy tonnage. The tides also prevent
the sea, which is the receptacle for a vast quantity of filth,
from becoming stagnant, which would infallibly happen unless
the perpetual oscillation of the tides purified its waters, by
propagating in all directions the salt which the sea produces,
and destroyed the putrefying matters that would otherwise
prove noxious to us.
IX.
Fig. 51.—Rhea (from the design of a Roman lamp).CHAPTER XI.
THE PLANET MAES.
Recent observations of the planet Mars—Its close analogies with the Earth—
Its reddish aspect—Its atmosphere — Its soil—Its different names—
Curious mistakes to which the distances of Mars from the Earth may
give rise—The seasons in Mars—Its poles of ice and snow—Its forests,
seas, and islands—Dimensions, translation, rotation, and phases of Mars.
I.
The planet Mars is our neighbour in space, and presents
such close analogy with our globe, both in respect to atmo-
spheric phenomena and polar cold, that anything appertain-
ing to it is specially interesting.
To the naked eye Mars does not appear to be very bril-
liant. To judge by its reddish hue, it must be surrounded
by a very dense atmosphere, greater than that of the Earth,
a theory which is confirmed by the fact that the stars by
which it passes disappear completely before the globe of
Mars eclipses them.
M. Arago says that its light is at times scintillating; but
some astronomers have attributed its reddish hue to the
constitution of its soil.
Sir John Herschel remarks that, “ in this planet we can
very plainly discern the outlines of what may be considered
as continents and seas. The continents are distinguishable
by that reddish colour characteristic of the light of this
planet, which seems to be perpetually in flames, and whichTHE PLANET MARS.
239
indicates beyond doubt that the soil is mostly ochre-
coloured, just as the quarries of red sand in certain parts of
our globe may seem to the inhabitants of Mars. The only
difference is that the tint is of a more pronounced shade,
owing to a contrast, which is attributable to the laws of
optics. The seas, as we may call them, appear to be of a
greenish hue.”
It is because of this reddish colour that in Hebrew the
name Mars signified ignited; with the Greeks, Mars, also
called Hercules, generally took the epithet of incandescent;
and the Indians called it Angaraka, which signifies burning
coal, and the red body.
II.
None of the planets can compare with Mars for its exces-
sive variations in brilliancy, which are due to the fact that
its distances from the Earth and the Sun undergo great
changes, according to its position in the sky.
Its ellipse is very eccentric: at the period of conjunction
it is about 245,249,000 miles from us; at the period of
opposition, only 62,389,000 miles. These very unequal
distances from the Earth lead to great variations in its
apparent disc. Thus, in the month of March, 1719, Mars,
being in opposition and also at its least distance from the
Sun, emitted so brilliant a light that many persons took
it for a newly discovered star, while those not versed in
astronomy were alarmed at its abnormal appearance. Its
ellipse varies but slightly from the plane of the ecliptic,
forming only an angle of 1° 51'.
The Sun is in the northern hemisphere during the half-
duration of the planet’s revolution, and afterwards in the240
ASTRONOMY.
opposite hemisphere. Thus, these two periods are sepa-
rated by equinoxes similar to those of the Earth, and for
the same reason Mars has seasons analogous to those of
our globe. This explains a singular phenomenon which
has been observed near the north and south poles of Mars;
viz., the growth and decline of two white spots, the bril-
liancy of which is double that of any other part of its
surface.
The northern spot diminishes in size during the spring
and summer of the northern hemisphere, and augments
during the two following seasons, the process being reversed
in the south pole. This indicates a successive formation
around the poles in Mars, of large caps of snow and ice which
increase and diminish in size according to the temperature.
Upon our globe the northern hemisphere comprises the
largest tracts of terra firma, but in Mars the reverse seems
to be the case, for it is only at the 60th degree of lat. S.
that the mainland in this planet begins, extending from the
north to the equator.
III.
The most favourable opportunity for studying the aspect
of Mars occurs when it is in opposition with the Sun, as
then it crosses the meridian at midnight, and is nearer to
the Earth than at any other period.
When Mars was in opposition during the month of April,
1856, Father Secchi distinctly recognised the two snowy
spots of the polar regions, and he ascertained that their
centres did not coincide with the poles of rotation, l^hese
two spots rapidly diminished in size when they became ex-
posed to the solar rays, but they increased both in extentTHE PLANET MARS.
Ml
and brilliancy as they moved away from the direct radiation
of the Sun.
The dark spots of various shapes which are visible
through a glass upon the disc of this planet are, on the
contrary, fixed bodies, which seem to form part of its surface;
but they vary in aspect just as our forests might do when
seen at different seasons and divergent latitudes.
During the summer of 1858, Father Secchi took advan-
tage of the opposition of Mars in the month of May, to
take a series of minute drawings of that planet, which the
use of the great equatorial (a telescopic instrument) at the
College of Rome enabled him to do. The colours of the
spots seem to vary much, some being red, others blue,
green, or white. The opposition of 1862 was taken advan-
tage of by many English astronomers. Messrs: Grow and
Joyson sent sketches of the planet to the Astronomical
Society of London, and Professor Phillips, of Oxford, pre-
sented The Royal Society with a series of drawings obtained
by combining his own observations with those of other astro-
nomers, which were intended to show the phenomena pre-
sented by Mars during the whole period of its relative
proximity to the Earth.
It was in such a position that the whole circle of snow
which surrounds the south pole was distinctly visible, and
its outlines were so clearly defined that the observers were
enabled to remark that it terminated in a steep declivity.
The snows of the northern hemisphere are but dimly
visible, and every thing tends to show that the white caps
are not all situated in the same hemisphere, if we may so
speak, of the planet.
The equatorial region is occupied by a large green belt,
with deep bays and receding inlets, which seem to indicate
RASTRONOMY.

Fig. 52.—Map of the planet Mars (after Maedler).THE PLANET MARS.
243
that this part of the planet is a mass of water. Atone
point in this region rises an island, which has the same
reddish hue as the two great continents above and below
the equatorial band.
M. Vinot says, that “ a very clear idea of the ordinary
appearance of Mars may be obtained by studying the map
of North America. Supposing the ocean which surrounds
America to be term firma, and America itself an ocean, we
get a very close likeness of wliat the astronomers term, in
Mars, the Ocean cle la Rue.” *
M. Stanislaus Meunier sees a proof of the great age of
Mars in the shape of its seas. It seems clear to his mind
that the seas on our globe will gradually assume the same
outlines as those of Mars when they have undergone a
certain diminution of volume, consequent upon tlieir pro-
gressive absorption by the solid nucleus.'t
M. Flammarion, in an interesting paper upon Mars, gives
the following compendious account of the facts which seem
to be placed beyond the possibility of doubt in regard to
this planet: 1st, the polar regions are alternately covered
with snow, according to the seasons and the variations due
to the great eccentricity of its orbit, the ice of the north
pole not at present extending beyond the ,80th degree of
latitude; 2nd, clouds and atmospheric currents exist there
as upon the Earth, the atmosphere being more charged in
winter than in summer ; 3rd, the geographical surface of
Mars is more equally divided than that of our plqnet into
continents and seas, the latter slightly predominating; 4th,
the meteorology of Mars is almost the same as that of the
Earth, the water having the same physical and chemical
* Vinot’s BvMdin Asironomique for 1873.
t Academia des /$'aettC£s-(Septeinber lst, 1873). .
r 2ASTRONOMY.
24.4
properties; 5 th, the continents seem to be covered with a
reddish vegetation; 6th, the force of analogy shows us that
this planet possesses, in a greater degree than any other,
organic conditions in close affinity with those of the
Earth.*
IV.
The apparent diameter of Mars varies from 18" to 4"; its
real diameter is 4,000 miles, its surface is only a third
that of the Earth, and its volume one fifth; its mass is but
a tenth that of our globe, and its weight scarcely half.
It receives only |ths of the heat and light which the Earth
receives from the Sun, and the latter luminary must appear
only a third the size it does to us.
Its mean distance from the Sun is 139,312,000 miles;
its revolution is accomplished in 686 days, 23 hours,
30 minutes, 41 seconds, which is almost double that of
the Earth. Its rotation takes 24 hours, 30 minutes, 21
seconds.
Mars is the only superior planet in which we can distin-
guish phases; the obscured portion of its disc never exceeds
an eighth of its total surface. At the epoch of its quadra-
tures it presents a more or less elongated oval shape, but
never that of a crescent.
Galileo, writing to Father Caselli on the 80th of Decem-
ber, 1610, says: “ Without positively asserting that I have
distinguished the phases of Mars, I am almost certain that
this planet is not quite round.”
Bicasoli says that, on the 24th of August, 1638, Fontana,
* Academic des Sciences (July 28th, 1873).THE PLANET MARS.
245.
of Naples, distinctly observed the absolute gibbousness of
Mars. This observation, at the time it was made, was un-
questionably a discovery of importance, but in the present
day the merest tyro in astronomy, who is in possession of a
good glass, can easily perceive the phases of Mars at the
epoch of the quadratures.CHAPTER XII.
JUPITER, SATURN, URANUS, NEPTUNE.
Jupiter—Its distance from the Sun—Its motions—Aspect of its surface—Its
dimensions—Its satellites—Their eclipses and the velocity, of light—
Saturn—Its distance from the Earth and from the Sun—Saturn’s ring—
Nature of this ring—Its aspect—Its dimensions—Various hypotheses—
Uranus—Its motions — Its dimensions—Its satellites—Neptune—Its
distance from the Sun—Its rotatory motion round the Sun—Its pcrtur-
bations.
L
Jupiter.—Jupiter is distant 475,093,000 miles from tlie
Sun. In the space of 11 years, 307 days, 14 hours, 18
minutes, 9 seconds, it travels over an orbit of more than
two and a half milliards of miles round the Sun, conse-
quently travelling at a rate of 25,000 miles an hour.
The motion of this planet upon itself is much more rapid
thali that of the Earth, taking place in 9 hours 56 minutes.
5 The' displacement of the spots which the telescope lias
discovered upon its disc, prove to us that Jupiter revolves
upon itself. Nearly all of these spots have the shape of longi-
tudinal hands, some of them obscure, and others luminous.
Their number varies very much, and sometimes they all
appear to he adherent, like long zones which envelop the
planet, while at other epochs there is a solution of con-
tinuity. While at one time only one or two are visible, at
another seven or eight can he seen.
At various intervals, too, certain veiy salient points
become visible, which deqote still more precisely the dailyJUPITER, SATURN, URANUS, NEPTUNE, HI
motion of this planet upon its axis. Some astronomers
consider these different spots to be seas dotted with islands,
and extending over the globe of Jupiter in the direction of
its rotary motion. Others, again, look upon the obscure
sections as constituting the body of the planet, and the
luminous sections as clouds driven by the wind in various
directions, and at varying speed.
M. Tacchini has communicated to the Academie des
Sciences (February 17th, 1873) the result of the observa-
Fig. 53.—The planet Jupiter, as seen hy Tacchini, at Palermo, on the night of
January 28th, 1878.
tions of Jupiter which he made at Palermo, in January, 1873,
accompanied by an engraving (see Fig. 53) representing
the aspect of that planet on the night of January 28th. He
states that it is not traversed by numerous bands, regular
i248
ASTRONOMY,
in shape, but that the surface is subdivided into clearly-
defined zones, the most irregular of which is that comprised
within the parallels aa' and bb'. The white parts of this
zone were bright, like silver; there were also some black
spots surrounded by the same white substance, and they
resembled small solar spots with very pronounced faculse.
Near the edge, between the obscure lines, dd' and ee', the
Surface appeared to be covered with whitish clouds, and the
two polar caps were of a slightly ashen tint. M. Tacchini
adds“ Comparing the present drawing and that executed
in 1872 with those taken in 1867 and 1871, it is evident
that Jupiter is in a period of variability.”
The least distance of Jupiter from the Earth, 408,709,000
miles, is too great to admit of our distinguishing its phases.
Its diameter is 85,399 miles, which makes it 1,387 times
larger than our globe.
As Jupiter is five times further from the Sun than the
Earth, the orb of day must seem only a fifth the size it does
to us, and transmit but a twenty-fifth part of the light and
heat which we receive.
But this deficiency may be partially compensated for by
the fact that its nights only last five hours, and that it
possesses four satellites or moons like ours, one of which at
least is always visible throughout these brief nights.
The first and the fourth of these moons are as voluminous
as Mercury. The second and the third are of about the
same dimensions as our satellite. The fourth seems
specially destined, by reason of the inclination of its orbit
to the equator, to give light to the poles in Jupiter.
All of these satellites revolve round Jupiter in the direc-
tion of west to east, and further resemble our Moon in that
they always present the same face, owing to the fact ofJUPITER, SATURN, URANUS, NEPTUNE.
249
their only making a single turn upon their axis, though still
accomplishing their complete revolution round the planet.
This has been concluded from the periodical return of the
spc ts observed upon their surface.
The first satellite is that nearest to Jupiter, the second is
the one next nearest, and so on.
The three nearest undergo an eclipse at each revolution,
hut the fourth, owing to the inclination of its orbit, only
falls within the shadow of Jupiter four years out of six.
These eclipses can be calculated beforehand, like those of
our Moon.
It was by means of these eclipses that Eoemer, the Danish
astronomer, succeeded in determining the velocity* of light,
having observed that they always occurred about 16' 36" later
when Jupiter was in conjunction with the Sun upon the other
side of the ecliptic, than when it was upon our side, in opposi-
tion. Whence he concluded that light took that time to
traverse the whole diameter of the terrestrial orbit; that is
to say, about 182,000,000 miles.
II.
Saturn.—Saturn's mean distance from the Earth is
922,640,500 miles, and, owing to its enormous distance, it
transmits to us a very faint light of a leaden hue.
Though 746 times larger than our globe, it only appears
to us the size of a star of the second magnitude. It is
about 872,135,000 miles from the Sun, and takes 29J
years to travel over an orbit of nearly five milliards of
miles round the Sun, at a velocity of 21,000 miles an
hour.
Seen from Saturn, the Sun must seem ninety times250
ASTRONOMY.
smaller than from our globe, and consequently transmit to
it a very trifling amount of light and heat. But, in addition
to eight moons which revolve around it, and give it their
light, Saturn is surrounded by two flat rings, wide and
shallow, both of which have the same centre as the planet.
They both repose in the same plane, being separated from
each other all along their circumference by a very slight
interspace, but they are farther removed from the planet
itself.
It would be difficult to make any positive statement as
to the nature of this double ring, but it appears to be
analogous to the planet itself, for it projects a very intense
shadow over it; and whenever the Sun and the Earth are
upon the side of this plane, the ring is luminous, whereas
when it occupies an intermediate position in respect to the
Earth and the Sun, that part which is turned towards us,
no longer receiving the solar rays, becomes altogether
invisible. This is a proof of its opaqueness, and that
its brilliancy or obscurity in relation to the Earth depend
upon the various positions that Saturn occupies in its
orbit.
It has also been remarked that, soon after its period of
brilliancy, the ring gradually contracts, owing to the dis-
placement of the planet in space, and eventually appears
only as a thin luminous line, which finally vanishes.
After a certain lapse of time the ring reappears, gradually
grows larger, and, swelling out to its greatest. breadth,
enables us to discern, in the interspace which separates it
from the planet, a part of the sky with the stars shining
in it.
This interspace is, according to Herschel, not less than
37,570 miles, the ring itself being 27,610 miles in breadth.JUPITER, SATURN, URANUS, NEPTUNE.
251
It is divided into two distinct annuli, separated from each
other by an always obscure space of 1,680 miles.
The inner ring, that nearest to Saturn, is 17,605 miles
in breadth; it is surrounded by the second, which is only
9,625 miles in breadth. The edges are not flat, but spherical
or rounded, and their base, which is about 90 miles, seems
to be dotted with several high mountains.
As this double ring has an inclination of 81° 35' towards
the plane of the ecliptic, we never see it except obliquely,
in the shape of an ellipse, the maximum width being about
half its length.
Mr. Hirne,-a corresponding member of the French Insti-
tute, deeming that the modern theories of thermodynamics,
which are partly based upon his own researches, might be
applied to celestial mechanics, commenced to investigate
this subject, and compiled a memoir upon the rings of
Saturn, which M. Faye read before the Academie des
Sciences (September 16th, 1872).
It is difficult to determine the nature of this double ring.
It has hitherto been considered analogous in character to
the planet itself, but Hirne, on the contrary, argues that
the rings of Saturn are not solid, circulating around the
planet in the plane of its equator, and ^ballasted at certain
points by a slight surplus of matter, so as to impart solidity
to their remarkable equilibrium; that they are not, again,
fluid or liquid rings, in which the mutual reactions of the
molecules tend inevitably to transform active force into heat,
which would be lost in space, but that they are simply
aggregations of disconnected matter, the parcels of which
are very widely separated from each other in proportion to
their dimensions. He goes on to demonstrate that this
theory coincides with Laplace’s idea as to the origin and252
ASTRONOMY.
Fig. 54.—Principal phases of Saturn as seen from the Earth.JUPITER, SATURN, URANUS, NEPTUNE.
253
formation of these singular appendages, but that the con-
densation caused by refrigeration must have produced an
infinity of distinct corpuscles, uniformly distributed in the
primitive rings, instead of gradually uniting them in isolated
masses like the satellites, or grouping them into continuous
solid and coherent rings, the formation and deportment of
which do not seem compatible with our actual notions about
physics, M. Faye adds, that astronomers, in their study
of the black shadow projected by the rings upon the planet
have also thought that they must be opaque and solid; but
that at the epoch of the last disappearance, in 1848 and
1849, it was' remarked that this opacity was by no means
absolute, for when the plane of the ring passed between
the Earth and the Sun the ring remained visible through
powerful instruments, on the side that was not in receipt
of light. It is true that astronomers have endeavoured
to reconcile this phenomenon with the hypothesis of solid
and opaque rings, by the introduction of a fresh hypo-
thesis, which consists in attributing to the rings’an atmo-
sphere of their own, capable of producing upon the non-
lighted face a faint crepuscular light. But, upon reading
Ilirne’s paper, M. Faye thinks it is far more probable that
the rings admit the passage of a few beams of light through
the interstices of their discontinuous elements,
During the discussion on this paper, M. A. Guillemin
quoted a well-known passage from the Elements of Astronomy,
by Cassini II., to the effect that the rings are beyond doubt
an aggregation of satellites, all of them situated in nearly the
same plan.* M. Volpicelli mentioned the fact that Bressel,
speaking of the eccentricity of Saturn’s ring, argued that it
was only to be explained on the hypothesis that this ring
* Academic des Sciences (September 23rd, 1872).254
ASTHONOMY.
lias no rotary motion, or tliat it consists of a large number
of parcels capable of independent motion. Moreover, in
the vocabulary of Marbach, we read:—“ As to the nature
of Saturn’s ring, it seems from probable analogy that this
ring consists of an accumulation of satellites, completely
tilling its orbit. It may be that these satellites are not in
contact with each other, but Saturn is too far removed from
the Earth to admit of our ascertaining the distance which
separates them.” *
Hirne’s assertion that the particles forming the ring are
separated by very large intervals of space seems scarcely
reconcilable with the fact of the ring projecting a shadow
upon the surface of Saturn (Academie des Sciences, October
21st, 1872).
Of the eight satellites of Saturn, four were discovered by
Cassini and Huyghens, two by Herschel, and one by Lassell,
at Liverpool, on the same night that Bond observed the
eighth, at Cambridge, in the United States. The surface
of Saturn shows several obscure bands parallel to the rings,
which Herschel attributed to a very dense cloudy atmo-
sphere, and, towards the polar regions, may also be discerned
certain white spots, which seem to be indicative of perpetual
snow.
III.
Uranus or Herschel.—This is one of the largest planets,
and, with the exception of Neptune, the farthest from the
Earth. It remained lost amongst the fixed stars until the
13th of March, 1781, when Dr. Herschel, then staying at
Bath, discovered it.
It is 1,758,851,000 miles distant from the Sun, around
* T. V., p. 356; Leipsic, 1858.JUPITER, SATURN, URANUS, NEPTUNE. 255
which it accomplishes in 84 years an orbit of about ten
milliards of miles, travelling at the rate of 16,000 miles an
hour.
The sunlight, which takes 8' 13" in its passage to the
Earth, must be nearly two hours and three-quarters in
reaching Uranus. The intensity of its light and heat cannot
be more than ^-R-, of what it is upon our globe, and the
Sun’s disc must seem no larger than a star of the first order.
Seen through the telescope, Uranus has an uniform bril-
liancy of azure white, and its disc is almost level at the
edges. It has a diameter of 83,024 miles, being, there-
fore, 72 times the size of the Earth. Herschel discovered
that six moons circulate around this planet, in orbs almost
circular and perpendicular to the plane of the ecliptic.
Neptune.—This is the most remote of the known planets
in the solar system.
It has a mean distance from the Sun of 2,746,271,000
miles, taking nearly 165 years to effect its total revolution
round that body. The immense distance, and the recent
discovery of this planet, are sufficient to account for the
slight knowledge which we possess concerning it. It has
not, since first discovered, completed more than a sixth
part of its orbit, having been observed for the first time but
eight-and-twenty years ago.
f M. Le Verrier announced its existence in 1846, basing
his inductions upon theories drawn from the disturbances
in Uranus, and it was actually observed by Galle, at Berlin,
on the 23rd of September in the same year.
The cause of the disturbances in Uranus had, however,
been guessed at for some time by Bouvard, Hansen, and
other astronomers, but the complete solution did not come
until 1846. Arago, in his Report upon the Progress of256
ASTRONOMY.
Astronomy (p. Ill), says:—“ M. Le Verrier perceived the
new planet without even taking a look at the heavens; he
saw it with the point of his pen, and, by the mere force of
calculation, determined the position and approximative size
of a body situated far beyond the hitherto known confines
of our solar system, of a body more than 2£ milliards
of miles distant from the Sun, and which, looked at even
through the most powerful glasses, is barely visible. Thus
liis discovery is one of the most striking manifestations of
the accuracy of modem astronomical science. It will
encourage the followers of geometry to seek with fresh
ardour those eternal truths which, to borrow the expression
of Pliny, * remain concealed behind the majesty of theories.’ ”
M. Delaunay insists that this discovery must not be con-
founded with that of several small planets which are situated
between Mars and Jupiter, and which have been discovered
by closely exploring those regions of the sky near the
ecliptic. “ The discovery of Neptune, on the contrary, is
the result of theoretical researches which have shown in
what part of the sky there must be such a planet, and this
ascertained, all that remained to be done was to bring the
glass to bear on that particular spot.”* Nevertheless,
Kepler (see page 34) had suspected the existence of some
star between Mars and Jupiter long before the discovery of
any of the small planets*
The research of the unknown planet, to which the dis-
cordance in the observed positions of Uranus and in the
tables drawn up by Bouvard, was attributable, became one
of the questions of the day, and astronomers generally gave
it their attention.
M. Delaunay thus describes the successful research of
# Delaunay’s Report on the Progress of Astronomy*JUPITER, SATURN, URANUS, NEPTUNE.
257
Le Verrier :—Having first gone through the calculation of
the disturbances in Uranus, due to the action of Jupiter and
Saturn, he found it necessary to make several additions to
modifications in the aggregate of the disturbances which
Bouvard had adopted as the theoretical basis of his tables.
He then examined a great number of meridian observations
of Uranus, taken some at Paris and others akjGreenwich,
since the discovery of that planet, as well as seventeen
observations anterior to its discovery. In this way he
deduced the impossibility of considering all these dis-
turbances as resulting only from the influence of Jupiter and
Saturn. He then proceeded to examine what part of the
sky must be logically occupied by the unknown planet
capable of producing the differences which take place
in the position of Uranus. Thus he succeeded in fixing the
longitude of this unknown planet, first relatively, and then
absolutely. The result of these theoretical researches was
soon confirmed, and Galle, an astronomer at Berlin, looking
for the planet in the direction indicated by Le Verrier,
lighted upon it immediately, and at the very spot which
theory had assigned to it. This was on the 23rd of Sep-
tember, 1846, and the star, which seemed to be one of the
eighth order, received the name of Neptune. It is impos-
sible to have a more striking proof of the precision of our
astronomical theories.
“ I must add that Le Verrier was not the only person to
study this important question, for Mr. Adams was examining
it in England at the same epoch. He arrived at the same
results, and though those of Le Verrier were published first,
both are entitled to share the credit of this astronomical
discovery.” *
* Delaunay's Rapport $ur Its progrls de VAstronomic, pp. 13, 14.
sCHAPTER XIII,
THE STARS.
Fixed stars—Wandering stars—Number of stars—The stars seen through the
telescope —Illusion caused by the aspect of the celestial vault—Distance
of the stars from the Earth—Bewildering calculation—The stars nearest
to the Earth—Stars of different sizes—The method of classifying and cal-
culating them—Number of stars of each order—The Milky Way—Its
nature and shape—From one surprise to another—The rank occupied by
our Sun in the creation—Incalculable number of suns—Ideas formerly
entertained concerning fixed stars—General motion of the whole solar
system in space—The laws of attraction in the most remote regions
of the sky—Planetary system of the stars—Double and treble stars—
Splendid revelation of spectrum analysis—Elements of which the stars
are composed—Types to which they appertain—Ideas concerning im-
mensity, and the stellar bodies which it contains—Division of the stars
into constellations—The constellations in ancient times—Historical and
legendary ideas—Northern constellations situated above the zodiac—Con-
stellations of the zodiac—Constellations situated below the zodiac.
I.
The generic word star is applied to all the celestial bodies,
but the planets have been more specially designated as
wandering stars, and the name fixed stars given to countless
twinkling bodies which seem to be distributed throughout
the immensity of the firmament, because it was formerly
believed that they did not revolve in orbits round a centre,
but that they always maintained the same relative situation
to each other* It has since been ascertained that many of
them have a motion of their own, and the presumption is
that such is the case with them all.
Their light is more brilliant than that of the planets, andTHE STARS.
259
is incessantly scintillating, that is to say, displaying a tre-
mulous luminosity.
On a fine night there seem to be millions of stars in
the sky, yet, even when the firmament is clearest, and at
the equator where half of it is visible, it is impossible to
count more than two thousand, without a telescope.
If Sirius, the finest star in the sky, is looked at through
a telescope of more than a thousand times magnifying
power, a tyro will be astonished to find that its volume, far
from appearing greater, becomes smaller; for the stars, seen
with the naked eye, always seem larger than they are in
reality, owing to the diffusion of light around their mass.
The telescope, consolidating the rays, destroys the irradi-
ation, so that the most brilliant star, seen through a good
glass, is so infinitely small in extent that we cannot measure
it. Thus, the most powerfully magnifying telescope is use-
less for observing the stars, while it amplifies very much the
other bodies to which we apply it such as the Sun, the
Moon, and the planets.
If we could rise above the Moon, approach the planets, or
reach one of the stars which shine above our heads, we
should discover new skies, new suns, new stars, new worlds,
perhaps more magnificent than that we now admire.
But the domain of the Creator does not end even there:
these are but the frontiers of the infinity of space. We
should behold other immensities peopled with other incal-
culable worlds. And if our journey were to last for tens of
thousands of centuries, we should never reach the limit
which separates the universe and God. In the presence of
such conceptions, calculation and poetry alike are dumb, to
use M. de Lamartine’s expression, and the boldest inquirer
is awed into silence.
s 2260
ASTRONOMY.
II.
The distance of the stars from the Earth is so great that,
supposing an observer transported into Sirius, one of the
stars nearest to our globe, he would see from there, at an
almost imperceptible angle, the whole space of 180,000,000
miles, comprised within the two extremities of the terrestrial
orbit, so that the Sun, the Earth, and the Moon, would
form but a point, no thicker than a single hair.
If an inhabitant of our globe could ascend to the height
of 180,000,000 miles, those three bodies would appear to
constitute but three brilliant specks.
We have the proof of this every year. About the 10th
of December, the Earth’s motion of translation round the
Sun brings us more than 180,000,000 miles nearer to the
stars in the northern part of the sky than we are on the 10th
of June, without our being able to perceive any increase in
their size.
Up to the beginning of the fourteenth century, the most
diligent studies of astronomers had failed to establish more
than the lowest limit of the distance between the Earth and
the stars.
Their calculations had demonstrated, by means of
absolute parallaxes, as this method is termed, that the stars,
of which they had endeavoured to fix the distances, must be
at least 40 trillions of miles away from us. Such a distance
is so difficult of conception, that the astronomers adopted
as an unit not the mile, but the space of 186,000 miles,
which light traverses in a second.
And as 40 trillions of miles are more than 108 mil-
lion times the multiple of 186,000 miles, it follows
that light, with its enormous velocity of 186,000 miles a
second, would take 203 million seconds, that is to say 2,850THE STARS.
261
days, or 6J years, to traverse the distance which separates
us from the nearest of the stars. It will be found, too,
that a cannon hall, with a velocity of 1,650 feet a second,
would take more than four million years to accomplish the
same distance, and that a fast train would take 144 million
years.
III.
Another method, called that of relative 'parallaxes, made
use of by modern astronomers to measure the distance to
the stars, has enabled us to ascertain many distances which
it had previously been impossible to determine.
The principal results obtained are as follows: The
least distant is the star Alpha, in Centaurus, which is about
5,865,556,000,000 miles away, and which it would take
light nearly four years to reach. Next comes star 61, in
Cygnus, the distance of which from the Earth would
only be traversed by light in years. After it come the
Alpha of Lyra, Sirius, Bootes, Arcturus, Capra, etc., the
distances of which are traversed by light in 12£, 22, 26, 31,
and 72 years.
Now, if we admit, as is often the case in natural sciences,
deductions by analogy, we arrive at results even more
astonishing.
It may be taken for granted that the stars which appear
the least brilliant to us are generally the most remote.
Starting upon this hypothesis, and connecting it with the
fact that light diminishes in intensity according to the
square of the distance, that is to say, appears only a quarter
as brilliant at double the distance, a ninth at treble, and so262
ASTRONOMY.
on, astronomers have been enabled to form an approximate
estimate of the distance of those stars which cannot be
measured directly.
In this way Herscliel calculated the relations between the
unknown distances. Stars of the second class he calculated
to be as a rule four times less brilliant, and consequently
twice as far as those of the first order; and the stars in the
fourth class to be in turn twice as remote as those of the
second. The distance of the stars in the fifth class he esti-
mated to be eight times, and those of the sixth twelve times
greater than that which separates us from the most brilliant
stars. The faintest which he could distinguish with his
ten-foot telescope, would be 344 times farther than the
latter; those seen through the twenty-foot telescope, 900
times. And as light takes twenty years to reach us from
stars of the first order, it must take eighteen thousand years
to come from the most remote stars which Herschel could
distinguish with his twenty-foot telescope.*
It must be added that this telescope did not penetrate to
the farthest limits of the starry sky, for Herschel states
that an instrument of forty feet, which does not, however,
appear to have been used for a comparison of intensity,
added considerably to the number of visible stars. More-
over, it is probable that the celestial regions are not in-
finitely transparent, in which case many of the fainter stars
would not be within the range even of the most powerful
instruments. Everything tends to show that these distances
quoted are almost microscopic in comparison with the actual
dimensions of the celestial regions.
* M. Petit’s Treatise on Astrology.THE STARS.
263
IV.
The stars appear to us to differ in size, and they have
been divided into seven classes.
The stars of the first magnitude are those which appear to
us greatest in diameter, and most brilliant; the other stars
visible to the naked eye are called stars of the second, third,
fourth, fifth, and sixth magnitude, according to their
apparent size and brilliancy.
Stars of the seventh magnitude are those which can only be
seen through the telescope, and as some of them are more
brilliant than others, they are subdivided into stars of the
eighth, and even the fourteenth magnitude.
The real size of these stars is unknown to us, and their
classification, not always very correct, is merely based upon
their apparent size. This classification was made by early
astronomers in a somewhat rough and ready manner, and
modem catalogues have not amended the errors.
The most reliable tests give seventeen stars of the first
magnitude, but it is impossible to guarantee the accuracy of
this estimate. There may be more, and there may be less,
for there is no perceptible difference between the last star of
the first magnitude and the first star of the second magni-
tude. These remarks apply with all the more force to the
stars of the succeeding magnitudes.
As to their real size, it may well be that those which
seem smallest to us are, as a matter of fact, the largest, the
size being merely a question of comparative distance.
V.
In the northern hemisphere there have been counted
4,300 stars visible to the naked eye. The operation oi count-264
ASTRONOMY.
ing is performed by piercing a very narrow hole in a screen,
and placing it so as to command the stars between the pole
and the equator. The stars which appear there in the
course of twenty-four hours are carefully noted down, and
their totality calculated by means of the following rule: It
has been ascertained that the number of stars of the second
magnitude is treble that of the primary stars, that stars of
the third magnitude are treble those of the second, and so
on. Starting upon this basis, we arrive at a total of 43
millions, but this rule evidently fails to give a sufficient
number when we come to estimate the stars of the seventh,
and still more those of the telescopic magnitude.
Upon part of the constellation of Orion, along a band 15
degrees long by 2 wide, Herschel counted 50,000 stars, a
proportion which, if maintained, would give a total of 59
millions for the whole sky.
But there are numerous regions of the sky where the
stars are much closer together, to say nothing of the vast
aggregations which the nebulae display.
As we can only discern the first zones of the firmament,
and as the stellar strata may be, and no doubt are, piled one
upon another almost to infinity in the depth of space, it
may well be said that the real number of stars is in-
calculable.
VI.
Examining the heavens at night, we notice a pale and
irregular light, forming a band or zone which extends
throughout the sky, and which, termed the Milky Way by
astronomers, is also known in France as Le Chemin de Saint
Jacques.THE STARS.
265
Ovid, in the first book of the Metamorphoses, says:
“ When the sky is clear a path of very radiant white colour
may be seen in the empyrean. It is called the Milky Way,
and along it the immortals repair to the august dwelling
place of the Lord of Thunder.”
This luminous track, resembling a light cloud, is formed
of countless stars which cannot be seen by the naked eye,
but which are visible through a powerful telescope. It is
because these stars are so far from us that they are not in-
dividually visible to the naked eye, while, between those
which can be seen with the aid of a good telescope, are in-
terstices which, to all appearance, are covered with a vast
quantity of other stars not within the range of any tele-
scope. The mind becomes confused when we reflect that
the stars visible in the milky way, though out of all
comparison larger than the earth, appear to us only as
luminous points, and no matter what instrument we use
they do not increase in volume, which is a further proof of
their prodigious distance from the Earth.
The milky icay comprises luminous matter, which is not
resolvable with our comparatively feeble instruments, aggre-
gations of stars, formed perhaps by the disintegration of
the Nebula, and simple stars of various sizes. Herschel
made a minute study of the milky way with his powerful
telescope, and while he sometimes observed as many as
600 stars within the arena of his instrument, at others he
could only see one. Certain parts of this nebula, as they
passed before his telescope, displayed as many as 116,000
stars in a quarter of an hour, and they were succeeded by
sections that did not contain a single one. In fact, so far
as we can judge, the milky way exhibits patches of diffuse
luminous matter, and many millions of stars, some isolated,266
ASTRONOMY.
others massed in groups, and forming in its totality a kind
of zone or ring, the diameter of which would be about six
times greater than its thickness, and of which our Sun
would form a part.
VII.
Herschel was led to conclude that the numberless stars
which compose the milky way constitute a mass of a more
or less lenticular form—the section of a sphere or a carriage
wheel, with the Earth at about the centre, and with a thick-
ness not more than the sixth of its diameter. Now, such a
mass as this would be likely, considering the profundity of
space, to present a spot of whitish colour, standing out upon
the background of the sky, and this appearance is as a
matter of fact presented by a multitude of small nebulosities
which powerful glasses have discovered in the firmament,
and which are at scarcely perceptible angles to the Earth.
Some of these spots, of these five thousand and more
nebulse, which have been catalogued, are certainly equal in
size to the nebula of which we form part, and the astro-
nomers who have attempted to calculate their distances
have arrived at figures which almost inspire a feeling of
terror. It has been estimated that light would not traverse
the distance between these nebulse and the Earth in less
than sixty million years, while a cannon ball would take
87,000 milliards of years !
And yet, M. Petit adds, there is no reason for supposing
that the created universe ends here. On the contrary, there
are a thousand motives for believing that if we could be
transported to these remote regions, we should find the
limits of the firmament as distant as ever, with now un-
known stars shining in another infinity of space.THE STARS.
267
Having ascertained the distance of certain stars, it was
relatively easy to determine the rank which our Sun occu-
pies in creation. This luminary, with a volume thirteen
hundred thousand times greater than that of the Earth,
would, if transported into the mean region of stars of the
first magnitude—that is to say, a million times more distant
than it now is—appear to us as a scarcely visible speck, as a
very small star of the fifth or sixth magnitude.
Thus the stars are themselves suns, and much larger, as
a rule, than that which illuminates our globe. Struwe has
calculated upon the data given by Herschel, that in the
milky way alone there are at least 20 millions of visible suns,
independently of those, far more numerous no doubt, which
we cannot discern there. Yet the milky way occupies but a
small corner of the universe, for astronomers have already
counted more than five thousand nebulae, several of which,
it appears certain, are as extensive and fully peopled with
suns as the milky way!
VIII.
The stars maintain, in relation to each other, positions
which were formerly considered as invariable; whence their
denomination of fixed stars. Ancient astronomers thought
that they were luminous points, adherent to the celestial
vault, and travelling with it every day in a common motion
from east to west.
It was not till the beginning of the eighteenth century
that the displacement of these celestial bodies was deduced
from a study of past records. In 1738, Jacques Cassini
demonstrated the change of position of Arcturus, and of
Alpha in Aquila; and in 1756 Tobie Mayer discovered that268
ASTRONOMY.
of eighty other stars. Since then the discoveries have been
so multiplied that what seemed a paradox a hundred years
ago is now a generally accepted truth, so much so that, in
1845, “ the British Association for the Advancement of
Science ” published a list of more than eight thousand stars,
tliree-fourths of which possess calculated motions of their
own. It is marvellous to think that millions of globes
similar to our Sun, twelve or fifteen hundred thousand times
more voluminous than the Earth, are travelling through the
immensity of space without coming into contact, at a speed
far greater than that of a cannon-ball, and yet appearing to
us quite motionless, except by the aid of the most powerful
instruments. We may well exclaim with the psalmist: “ The
heavens declare the glory of God ! ”
After a number of calculations based upon the motion of the
stars, and very minutely carried out. Sir William Herschel
succeeded in proving that the Sun moves with the Earth
towards those stars which seem gradually to increase the
distance between each other, and that on the other hand it
recedes farther away from those which appear to draw closer
together. Subsequent to 1783, when his researches were
made, numerous facts have come to light, tending to con-
firm the truth of this theory. The best authenticated data
attribute to the Sun, and therefore to the Earth and the
whole solar system, an annual progress of nearly 300,000,000
miles towards the stars y and 6, of the group known as
the constellation of Hercules. This gives a daily progress
of about 800,000 miles.
IX.
The laws of attraction extend to the most remote regions
of the sky, and Herschel was the first to observe in many ofTHE STARS.
the binary groups the mutual dependence of two stars upon
each other; to these he gave the name of double stars. Some-
thing analogous appears to take place in the groups, of which,
however, there are not so many, formed of three, four, or even
a greater number of stars, which have been termed multiple
stars. From the few motions which it has been possible to
observe, it has been ascertained that the satellite star
describes around the principal star an ellipse of which the
latter does not occupy the centre.
The two stars which together constitute a double star,
move around each other, and M. Delaunay says that this
common motion was traced by Savary about forty years ago
to the great law of universal gravity. M. Yvon Yillarceau
also took up this important question, and he has drawn up
new formulae for determining the orbits of the double stars,
and has put it into practical application for several of them.
Father Secchi says: “ The stars are divided into groups,
which form systems similar to that to which we belong.
The laws of attraction produce and regulate the motions of
these distant bodies, as well as the circulation of the planets
round the Sun. The simplest systems constitute the double
or treble stars; they are so many suns with their cortege of
planets describing elliptic ellipses around them. These
planets only differ from ours in one respect; they are still
incandescent, and therefore luminous of themselves, reflect-
ing their own light to us, and not that which they reflect
from other bodies. This circumstance permits us to see
them from so great a distance, to observe the positions
which they successively occupy, and to calculate the orbits
which they describe.” *
We are even in the way of discovering that the stars have
* Father Secchi on The Sun, p. 404.270
ASTRONOMY.
obscure satellites. The irregularities observed in the
motion of Sirius had long raised the suspicion that some
similar body must circulate around this magnificent star;
but when this satellite was discovered it proved to be
luminous of itself, and as brilliant as a star of the sixth mag-
nitude. It is, however, shrouded by the dazzling brightness
of Sirius. Another star, Algol (/3 of Perseus), also affords
us direct proof of the existence of obscure satellites by the
regular variations to which it is subject, and which can only
be occultations produced by an opaque body passing across
the luminous star. These variations are phenomena iden-
tical in character with our eclipses, a fact which, long
guessed at, has been placed beyond doubt by recent spectro-
scopic discoveries.
The name of double stars has also been given to those
which are near enough to influence each other through
gravity, and to form a separate system. So far we only un-
derstand fifteen of these systems sufficiently well to be able
to fix with precision their revolutions, and to calculate the
elements of their orbits; but there are a great many others.
Further researches will unquestionably augment the number
of binary and tertiary systems. The binary systems present
two remarkable peculiarities; their orbits are generally very
elongated, and the two stars have nearly always comple-
mentary colours, which indicate a difference of temperature,
and a different state of condensation. Moreover, as Father
Secchi remarks (The Sun, p. 407), there are groups of stars
in the sky which we must recognise as forming symptoms
physically connected, as, for instance, the Pleiades, the
group of Cancer, that of Perseus, certain immense nebular
spaces, such as the Coma Berenices, the Magellanic clouds,
and especially the Milky Way.THE STARS.
271
X.
One of the most remarkable points connected with the
stars is the periodical variations which many of them un-
dergo ; for instance, one of them situated in the neck of Cetus
seems to he of the second magnitude when at its brightest,
preserving these dimensions and brilliancy for a fortnight,
then gradually diminishing until it disappears altogether,
only to reappear three hundred and thirty days afterwards.
Another, in the breast of Cygnus, has a period of fifteen
years; it appears during five years, with variations of bril-
liancy and size, and then becomes invisible for ten years.
Another, in the beak of Cygnus, has a period of thirteen
months; and in 1770 and 1771 another star was observed in
the same constellation, which disappeared in 1772, and has
not been seen since.
The star discovered in 1704, by Maraldi, in the constel-
lation of Hydra, appears during foiir months, and then
vanishes, only to reappear twenty months afterwards. Its
period, therefore, must be two years.
Several astronomers think that these stars are not bril-
liant all over their surface, and that, turning upon their axis,
they present to us at one time their luminous, and at
another their obscure hemisphere. Others argue that
opaque bodies circulate around these stars, and from time
to time become interposed between them and the Earth.
However this may be, such phenomena indicate great
activity in regions from which we might be inclined to think
that life and motion were utterly excluded.
There is a mass of undisputed evidence, dating from the
most remote times, to show that certain stars were in former
days more brilliant than some others, which are now in turn272
ASTRONOMY.
far brighter than the first. In the days of Eratosthenes,
Antares was less brilliant than one of the two stars in
Libra; but within the last century alterations of this kind
falsify in several constellations the order of the stars, as
arranged according to the letters of the Greek alphabet, in
comparatively modern catalogues.
XI.
Spectrum analysis has disclosed to us the elements of
which certain stars are composed, and I will append a suc-
cinct account of the reliable results which Father Secchi
has arrived at in his study of this subject.
For the purposes of spectrum analysis the stars belong to
four perfectly distinct types, though certain of the spectra
seem rather to serve as connecting links between the classes
than to belong to any one of them. The first type is that
of stars generally called white, though in reality they have a
slightly blue tint, such as Sirius, Vega, Altair, Kegulus,
Eigel, etc.
These stars have a spectrum formed of the usual group of
the seven colours, traversed by four thick black lines, one
in the red, another in the greenish-blue, and the two others
in the violet. These four rays are characteristic of hydro-
gen, and they coincide with the four more brilliant rays
which are visible in the spectrum of this gas when it is
raised to a high temperature. Other rays reveal the pre-
sence of sodium, magnesium, and iron. The most notable
peculiarity in this type is the breadth of certain rays, a fact
which tends to show that the absorbing stratum is very
thick, and subject to great pressure.
Nearly half of the stars in the sky belong to this type.THE STARS.
273
(For the classification, see Chromolithograph, No. II.,
Chapter 3). The second type is that of the yellow stars,
the spectrum of which is exactly similar to that of our Sun,
showing some very fhin, black rays, close together; this
type comprises Cassia, Pollux, Arcturus,Aldebaran,Procyon,
&c., nearly two-thirds of the remaining half. The stars in
this second category, having the same composition as the
Sun, are in the same physical condition.
The third type is that of stars approaching red or orange
in colour, such as a of Hercules, j8 of Pegasus, o of Cetus, a of
Orion, Antares, &c. Their spectrum is composed of a
double system of nebulous bands and black rays, the latter
being the same as in the second type. Most of the domi-
nant rays in this type belong to metals which have been ob-
served in the Sun, such as magnesium, sodium, and iron,
and those appertaining to hydrogen have also been remarked.
This spectrum is in all points similar to that of the solar
spots, which would seem to indicate that the stars of the
third type only differ from those of the second in the thick-
ness of their atmosphere and the want of continuity in their
photospheres, and that they have spots like those of the
Sun, but incomparably larger.
The fourth type appertains to small stars of a blood-red
colour, which are by no means numerous. Their spectrum
contains three fundamental zones, red, green, blue. Some
of the chief black rays very nearly coincide with those of
the third type. The very few stars in the fifth category
show a direct hydrogen spectrum.
To conclude this portion of my subject, I will quote the
following remarks by Father Secchi:. “What are we to
think of these vast expanses and the stars with which they
are peopled; stars which are, no doubt, like our Sun,
Tm
ASTRONOMY.
centres of light, heat, and activity, destined, like it, to sus-
tain the life of countless creatures ? It would be absurd for
us to imagine that these vast regions are untenanted deserts;
they must be peopled with intelligent and reasoning beings,
capable of knowing, honouring, and loving their Creator ;
beings, perhaps, more faithful than we are towards Him
who raised them up out of nothingness.” *
XII.
DIVISION OF STARS INTO CONSTELLATIONS.
To facilitate their study, stars have been divided into con-
stellations, which have received the names of men, animals,
and mythological objects.
The different stars forming a particular constellation have
been designated by the letters of the Greek alphabet, the
letter a being the most brilliant, and so on.
The Chaldseans are generally looked upon as the earliest
astronomers, and they were the first to classify the known
stars into constellations. The book of Job refers to the
Secret Chambers of the South, which may be taken to signify
the constellations near the South Pole, and it is generally
supposed that the Sacred Book contains an allusion to
Scorpio and Taurus. The only constellations alluded to
either in the Book of Job, Homer, or Hesiod, are Ursa
Major, Bootes, Orion, Canis Major, the Hyades, the
Pleiades, Scorpio, and Taurus.
In the year 125, b.c., Hipparchus made a catalogue, sup-
posed to be the first ever compiled, of the stars, with a
description of their size, position, longitude, and latitude.
The following are some of the legends attached to the
* Father Secchi on The Sun, p. 418.THE STAR#.
275
names bestowed on the constellations, many of which are
taken from Ovid.
The nymph Callisto, one of Diana’s attendants, had
offended Juno, who took vengeance upon her, by changing her
into a bear. Though thus transformed, she still retained
her natural instincts, and, herself a beast of the forest, fled
with terror from the others. Her son Areas, whom she had
borne to Jupiter, was hunting one day in a wood, and not
recognising his mother in the she-bear, was about to slay
her, when Jupiter warded off the blow, and whirling them
both into space, changed them into two neighbouring con-
stellations : Ursa Major and Ursa Minor.
Cassiopea, the wife of Cepheus, King of ^Ethiopia, and
mother of Andromeda, having boasted that she was more
beautiful than the Nereides, Neptune sent a sea monster to
ravage ^Ethiopia; and to appease him Andromeda was ex-
posed to a rock, but delivered by Perseus, whom she after-
wards married. Jupiter placed Cassiopea in the rank of
constellations.
Perseus, the husband of Andromeda, was the son of
Jupiter and Danae; he slew Medusa, the most formidable of
the three Gorgones, built the city of Mycenae, and after his
death he also was placed amongst the constellations.
Cepheus, son of Phoenix, King of ^Ethiopia, espoused
Cassiopea, who bore to him Andromeda. He accompanied
the Argonauts in their expedition after the golden fleece.
At his death he was placed by the Gods in the constella-
tions, so that he might be with his wife and daughter.
The famous horseman, Trethon, King of Athens, was the
first man who drove four horses abreast, and as a reward
Jupiter put him amongst the constellations. He is termed
the Waggoner (Charles’ Wain).276
ASTRONOMY.
Lycaon, having served up his grandson Areas to Jupiter,
whom he was entertaining, the divinity resuscitated him,
and placed him in the constellations. He is called Bootes,
or Arctophylax, the bear-keeper.
Berenice was the wife of Ptolemy Euergetes, King of
Egypt. Her liuvhand having undertaken a perilous expedi-
tion, Berenice made a vow to consecrate her hair to Venus
if he came back in safety, and on his return cut it off,
and deposited it in the temple. The hair having disap-
peared soon afterwards, Conon, the astronomer, to curry
favour, insinuated that Jupiter had placed it amongst the
stars. This is the constellation termed Coma Berenices.
Arion, a famous lyric poet and musician, was a son of
Cyclos of Methymna. He amassed great wealth by his pro-
fession, and on his return from a voyage to Sicily the sailors
resolved to murder him for his money. They allowed him,
however, to play some tunes before putting him to death;
the music attracted the Dolphins, and Arion, jumping
overboard, was carried on the back of one of them to
Taenarus, whence he hastened to Periander, who crucified
the sailors when they reached the port. At the request of
Apollo, the god of music, Jupiter made the Dolphin a con-
stellation of nine stars.
The Emperor Adrian was very much attached to a young
man of great beauty, called Antinous, who gave himself up
as a voluntary sacrifice to propitiate the gods. Adrian,
in remembrance of his self-devotion, raised a temple
to him, and named after him a recently-discovered con-
stellation.
Venus and Cupid, to escape from the giants that were
pursuing them, transformed themselves into fish, and swam
across to Syria. This is why the Syrians at one time re.THE STARS.
277
framed from eating fish, and is the origin of the constellation
Pisces.
A ram with a golden fleece saved Phryxus and Helle
from the wrath of Ino, daughter of Cadmus, their step-
mother. Phryxus immolated this ram to Jupiter, and sus-
pended his fleece in the temple. Jupiter accepted the
sacrifice, and placed Aries in the constellations.
Castor and Pollux were the sons of Jupiter and Leda.
Castor having been killed at the siege of Sparta, his brother
implored Jupiter to bestow upon him half of his own life, so
that each should live on alternate days, and the Thunderer
recompensed this rare display of fraternal affection by
placing the two brothers in the sky.
Cancer was made a constellation at the prayer of Juno,
because it had been killed by Hercules, for having bitten
him in the foot during his combat with the hydra of Lerna.
Orion represents one of the most beautiful constellations in
the sky. He was a famous giant and hunter, the reputed son
of Hyrieus, a Boeotian peasant; but really the son of Jupiter,
Neptune, and Mercury, who having been hospitably enter-
tained by the widower Hyrieus when travelling in disguise,
granted him a son by ordering him to bury, full of water,
the skin of the ox sacrificed to them. In this skin was
subsequently found Orion, who demanded in marriage the
daughter, Hero or Merope, of King (Enopion of Chios. He
afterwards became an attendant of Diana, who conceived a
deep passion for him, but Apollo, indignant at her love for
a mortal, asked her to shoot at an object in the sea, which
turned out to be Orion. He was afterwards placed in the
sky as a constellation, seventeen stars forming the figure of
a giant, with a girdle, sword, and lion’s skin about him.
Orion boasted that he could subdue the fiercest monsters,278
ASTRONOMY.
and another legend recounts that he was killed by the bite
of a Scorpion, which was placed in the heavens as a warning
to men against being boastful. Orion’s dog had such great
speed that he surpassed all the other animals, but being
pitted against a fox to which Jupiter had given an equal
degree of speed, he was carried up into the heavens, lest
the Fates should be unpropitious to him. This is the con-
stellation of Canis Major.
The constellation Canis Minor is so called in memory of
a dog for the great grief he had exhibited at the death of
Icarus, his master.
Phaethon, son of Phoebus and Clymene, once asked per-
mission to drive the chariot of the Sun one day in the sky,
but taking the horses out of the track, he nearly set the
universe on fire, and was precipitated by Jupiter into the
Eridanus (R. Po). This is why that river was placed
amongst the constellations.
Chiron, a centaur, was famous for his love of music,
medicine, and shooting, and he had for his pupils the
greatest heroes of the age, such as Achilles, Aesculapius,
Hercules, Jason, Peleus, jEneas, &c. He was accidentally
wounded in the knee by Hercules with a poisoned arrow,
while pursuing the centauri, and having in his agony prayed
Jupiter to deprive him of his immortality, he was placed by
that god as the constellation Sagittarius. In the same
region of the sky are the three following constellations :—
Corvus and Serpens, with the sign of Crater (the Cup)
between them. The following legend attaches to all three:—
Phoebus, who was preparing a solemn feast for Jupiter, sent
a crow, his favourite bird, to fetch some spring water in a
golden cup. The crow, attracted by some figs growing on
a tree, which were not yet ripe, sat perched on a tree waitingTHE STARS.
279
until they came to maturity, and, to conceal his misconduct,
flew back to Phoebus with a large serpent in his claws,
which he declared had prevented him from taking any water
out of the spring. Phoebus, to punish him for his double
fault, decreed that as long as the figs hung on the tree, he
should not be allowed to taste any water, and he let the cup
stand full of water, with the serpent close by, to prevent the
crow from tasting it.
The goat which was reared with Jupiter on Mount Ida
scattered terror amongst the Titans, who were attempting
to escalade Olympus. The gods, struck with terror, changed
themselves into different kinds of animals, Diana into a cat,
Apollo into a stork, Mercury into an ibis, Pan into Capri-
cornus, which is now one of the signs of the Zodiac.
Ganymede while hunting on Mount Ida was carried away
by an eagle to Jupiter, and became cup-bearer to the gods.
Hence the constellation Aquarius.
Hercules, while travelling with his wife Deianira, came to
the river Evenus, which was overflowing its banks. The
centaur Nessus offered to convey them across, and took
Hercules first, and then attempted to carry off Deianira. Her-
cules shot him with a poisoned arrow, and the dying centaur,
wishing to be avenged, gave Deianira his tunic, covered with
his poisoned blood, and told her that it would at any time
reclaim her husband's affections if he should prove faithless.
Some time afterwards, while he was raising an altar to Jupiter,
on Mount (Eta, she sent it to him as a philtre, not knowing
it was poisoned. When Hercules put it on he was attacked
with incurable pains, but he mastered the agony sufficiently
to erect a large funeral pile, which Jupiter surrounded with
smoke, and when his mortal parts were totally consumed he
was carried up to the heavens and placed amongst the stars.280
ASTRONOMY.
There is no need to relate the well-known allegories of
Orpheus bewailing his beloved Eurydice on the Lyre; of
the Dragon keeping watch over the garden of Hesperides;
of Cygnus and Taurus, into which animals Jupiter changed
himself; of the Lion slain by Hercules in the forest of
Nemea: all mythological figures which have lent their
names to constellations*
XIII.
NORTHERN CONSTELLATIONS SITUATED ABOVE THE ZODIAC.
1st. Ursa Major or Charles9 Wain.—This constellation is
composed of seven bright stars, four of which form a square,
and the other three, representing the tail of the bear, or the
pole of the waggon, a curved line.
Six of the seven stars in Ursa Major are of the second
magnitude, or secondary; the seventh, a tertiary star, is at the
angle of the square from which the tail of the bear springs.
The two stars forming the short side of the square oppo-
site to the tail are called the Guardians. The bear’s pairs
are represented by stars situated between Ursa and Leo.
2nd. Ursa Minor, or the Little Wain, nearer to the pole
than Ursa Major, is also formed of seven stars, forming a
somewhat similar figure; but they are less brilliant, and the
figure is not so distinct as in Ursa Major, being also turned
in an opposite direction.
The star situated at the extremity of its tail is called
the Polestar, and it is a bright secondary star, 1° 39'
from the pole. It is all the more easily noticed, as being
the only secondary star in this region of the sky, and as it
is in the direction of the Guardians of Ursa Major it can beTHE STARS.
281
discerned at once by drawing an imaginary straight line
through the two Guardians.
3rd. Cassiopea is situated upon the other side of the pole
relatively to Ursa Major, and is easily to he distinguished
by its five tertiary stars in the shape of the letter M.
4th. Cepheus is formed of three tertiary stars in the shape
of a bow, and of five stars of the fourth class ; it is nearer
to the pole than Cassiopea. The prolongation of the line
from the Guardians of Ursa Major, which enables us to fix
the Polestar, passes to the north of the bow of Cepheus.
5th. Draco.—This constellation displays a long row of
doubly sinuous stars. The tail of the Dragon separates the
two Ursce. The body folds round Ursa Minor, first ap-
proaching near to Cepheus, and then folding back almost
on to the head, which is formed of four stars, which is easily
visible by continuing the straight line through Cepheus and
Cassiopea.
6th. Pegasus has the shape of a somewhat elongated
square, of which the corners are four secondary stars. If a
line be drawn from the Guardians of Ursa Major to the Pole-
star, and thence prolonged twice as far, it will pass through
the square of Pegasus, which is on the opposite side of the
pole to Ursa Major.
7th. Andromeda is the most northerly of the four corners
in the square of Pegasus. The straight line between it and
the Polestar passes through the most brilliant star in the
constellation of Cassiopea. It comprises three secondary
stars, almost equi-distant, and forming a slightly curved
line.
8th. Perseus. The most brilliant star in Perseus, which is
of the second order, is situated between two tertiary stars,
the three forming an arc slightly convex towards Ursa282
ASTRONOMY,
Major. From the extremity of this arc start two rows of
stars, the one running eastward towards Capella, and com-
pleting the arc of Perseus; the other southward, pointing,
after a bend in the opposite direction, in a straight line
towards the Pleiades.
Underneath the most brilliant star in Perseus is Algol, or
Medusa's Head. This star is a variable one, remaining for
two and a-half daj7s as a secondary star, when its brilliancy
suddenly fades, and in the space of three hours it becomes a
star of the fourth magnitude; soon, however, to regain its
former brilliancy.
9th. Auriga is a large irregular pentagon, situated to the
east of Perseus. The three most brilliant stars form an
isosceles triangle; the apex, which is also one of the horns
of Taurus, is at the base, and the base contains the star of
Capella in the continuation of the belt of Perseus.
Abliaiot, or Capella, is a star of the first order. Close to
it are three small stars called the Capri, forming an isosceles
triangle.
10th. Lynx is a constellation of no great importance,
situate between Auriga and Ursa Major, below the latter.
11th. Leo Minor, composed of six stars, is upon the
southern section of the line, drawn from the Guardians of
Ursa Major.
12th. The Triangular Borealis is formed of three stars in
the shape of an isosceles triangle, between the foot of
Andromeda and Aries.
13th. Camelopardalis, a scarcely visible constellation, is
between the Polestar and Auriga.
14th. Bootes contains a star of the first magnitude, called
Arcturus, situated in a somewhat curved line beyond the
tail of Ursa Major,THE STARS.
283
Close to Arcturus, and to the north-east, is the irregular
pentagon of Bootes, the three northern stars of which form
an isosceles triangle. The raised hand of Bootes is formed
of four stars of the fourth order, situated close to the extre-
mity of the tail of Ursa Major. By this hand Bootes holds
two greyhounds, situated under the tail of Ursa Major, and
the neck of one of them contains a tertiary star known as
Cor Caroli.
15th. Coma Berenices (which is also called the Wheat-
sheaf) is composed of a group of small stars very close to
each other, and it is situated between Virgo and Cor Caroli,
below Ursa Major, and near the tail of Leo.
16th. Corona Borealis is composed of thirty-three stars,
six or seven of which form a semicircle, with its concave
surface facing the head of Draco. The most brilliant of
these is of the third magnitude, and is called Clara Coronce.
17th. Lyra is composed of twenty-one stars, one of which
is a splendid primary star called Vega, forming, with two
other tertiary stars, an isosceles triangle, which renders it
easy of recognition.
18th. Aquila, or the Eagle, is situated to the south of
Lyra. It is easily distinguished, as it contains three
remarkable stars in a straight line. The middle one is
called Altair, and is of the first magnitude; the other two
being of the second.
19th. Cygnus or Crux, is composed of five principal stars,
which form a cross in the milky way. The most northerly
of these stars is of the second magnitude, and is known as
the tail of Cygnus. The most southerly one, which is of the
third class, is called the beak of Cygnus. This constella-
tion is situate eastward of Lyra, and diametrically oppo-
site to Gemini in respect to the poles.284
ASJRONOMY.
20th. Serpens and Serpentarius (or Ophinchus).—These
two constellations occupy a vast expanse in the sky. The
head of Serpentarius is indicated by a secondary star. The
head of Serpens is situated below Corona Borealis, and re-
sembles the letter Y, the tail of which is formed of two
tertiary stars, between them being the heart of Serpens,
which is also a secondary star. The rest of the body is
formed of a row of tertiary stars, and extends to some
distance below the equator.
21st. Sagitta is composed of eighteen stars of the fourth
and fifth magnitude, and is close to Aquila, between Altair
and the foot of the cross in Cygnus.
22nd. Hercides.—The main part of this constellation is
formed of a quadrilateral of four stars in the fourth category.
A straight line drawn from Vega to Clara Coronse intersects
the quadrilateral of Hercules, which is equi-distant from
them both. The head of Hercules, which is a tertiary star,
is close to that of Ophinchus.
23rd. Delpliinus is a constellation composed of five prin-
cipal stars, one of which is tertiary, and to the south of the
four others, which form a small lozenge.
24th. Antinous is just below Aquila, and is composed of
six principal stars, four of which form a quadrilateral. The
eastern one is in a straight line with the three stars in
Aquila.
25th. Eqmdeus is between the constellations of Aquila
and Pegasus, and is composed of four stars, which form an
irregular square, the longest sides of which extend from
north to south.THE STARS.
285
XIV.
SIGNS OR CONSTELLATIONS OF THE ZODIAC.
1st. Pisces.—This constellation, in degree 342 of the
ecliptic, extends from 18° to 36°, which is the equinoctial
point, and the beginning of the sign of Aries. The Pisces
extend 42° farther, so that they embrace altogether 60°, or
the expanse of two signs. The first twelve degrees of this
constellation also belong to Aquarius, and its last to Aries.
It is composed of two stars; one, called Piscis Orientalis,
is situated above the ecliptic, beneath Andromeda and
Triangulus; the other, called Piscis Occidens, is close to
the ecliptic. The Pisces are connected by two rows of very
small stars, both of which are united to a tertiary star or node.
2nd. Aries occupies only 20° 17' in the sign of Taurus,
and contains only three important stars. It forms a sort of
circumflex accent above the ecliptic.
3rd. Taurus occupies 10° in the sign bearing that name,
and 22° in the sign of Gemini, which contains its head.
The head of Taurus forms a letter F, with its base towards
Aries, and its two points towards the milky way. One of
these points is marked by a bright star of the first order,
called Aldebaran, or The Eye of Taurus, which is conti-
guous to a small star near the milky way. The other point
is indicated by a star of the second order, and the two
represent the horns of Taurus.
4th. Gemini.—This sign is a long and irregular quadri-
lateral, formed of four principal stars, two of which are
secondary, and situated to the east of Taurus. They repre-
sent tixefeet of the Gemini, the heads being indicated by two
bright stars. Castor, a star of the first order, is situated to the286
ASTRONOMY.
north, nearest to the pole and the milky way. Pollux, a
star of the second order, is farther removed.
5th. Cancer is composed of stars which are not easily
distinguished. It is between Gemini and Leo.
6th. Leo occupies 38° in the zodiac, and lias four brilliant
stars forming a large trapeze beneath Ursa Major. A
straight line drawn from the two stars in the square of Ursa
Major nearest to its tail would, if prolonged, intersect
Regulus, or the heart of Leo, which is a very bright star of
the first class, situated just above the ecliptic. The head,
which is higher up, and is composed of four small stars
bordering on Cancer, contains one brilliant star.
7th. Virgo.—A long diagonal line drawn southwards from
the square of Ursa Major, strikes a brilliant star of the first
class known as the Spica Virginis. This constellation is in
the shape of a very open letter F, and is made up of five
tertiary stars, of which the one nearest to Coma Berenices is
called Vendemiatrix.
8th. Libra is upon the continuation of a straight line
drawn from Regulus in Leo to Vendemiatrix in Virgo. Two
bright secondary stars form the two scales of Libra, and two
other tertiary stars give it the shape of an oblique quadri-
lateral.
9th. Scorpio is composed of six principal stars, very sym-
metrically situated, three of them form an almost straight
line from north to south, and three from east to west. The
middle star of the three latter, of the very first class and
very brilliant, is called Antares, or the heart of Scorpio.
10th. Sagittarius is the constellation which follows next
after Scorpio across the meridian. Very easily distinguished,
it is partly in the milky way, and is in a direct line between
the central parts of Cygnus and Aquila.THE STARS.
287
11th. Capricornus, composed of five principal stars of
the third magnitude, is to the east, in a line drawn from the
beak of Cygnus, and passing close to the head of Aquila.
12th. Aquarius is not very easily discerned, as its brightest
stars are only of the third order. It is just to the east of
Capricornus, and extends from Delphinus to Fomalhaut
or the mouth of Piscis Australis.
XV.
PRINCIPAL CONSTELLATIONS BELOW THE ZODIAC.
1st. Orion is the most remarkable constellation in the sky.
It is composed of eleven principal stars, two being of the
first magnitude, four of the second, two of the third, and
three of the fourth and fifth. It is situated below Auriga,
between Gemini and Taurus, and is in the shape of a large
quadrilateral, the diagonals of which are formed of two
secondary and two primary stars. At the north-east angle
is the right shoulder, a star of the first order, and at the
south-west angle is the left foot, represented by a star of the
first magnitude, called Rigel. In the middle of the quadri-
lateral are three stars of the second magnitude, called the
belt of Orion, or the girdle, the Three Wings, the Rake, or
JacoVs ladder.
2nd. Cetus is a large constellation to the south of Aries,
and below the region which separates the Pleiades and
Pegasus.
3rd. Corvus is in the shape of a large trapezium, and is
composed of four principal stars, to the south of Virgo,
close upon the line from Lyra to Spica Virginis.
4th. Lepus forms a quadrilateral of four stars, of the
third magnitude, just below Orion, and to the right of Canis
Major.288
ASTRONOMY.
5th. Crater is situated to the rear of the hind feet of Leo,
and is composed of stars of the fourth magnitude, which
form a semicircle, to the right of Corvus. Other stars below
the semicircle form the base of the cup (Crater).
6th. Hydra occupies the quarter of the horizon below
Cancer, Leo, and Virgo. To the left of Procyon is the head
formed of four stars of the fourth order. A lino drawn
from the western side of the great trapeze of Leo, will meet
the primary star, Alfrqf\ or the heart of Hydra. A row of
ten stars composes the folds of Hydra, who carries on his
back Corvus and Crater.
7th. Eridanus, composed of a long train of stars of the
third and fourth classes, begins at the feet of Orion, close
to Bigel, bends back upon itself below Taurus and Cetus,
and terminates beneath the horizon with a star which is in-
visible at Paris.
8th. Canis Minor, situated between Hydra and Orion,
comprises a brilliant star of the first order, called Procyon,
to the north of Sirius and below the Gemini. A tertiary
star, close to the feet of the Gemini, represents the jaws of
Canis Minor.
9th. Cams Major, situated at the feet of Orion, is mainly
composed of five secondary stars and Sirius, the latter being
the largest and most brilliant in the whole sky.CHAPTER XIV.
THE COMETS.
Description of a comet; its different parts—Tho nature of comets—The
opinions of modern and ancient astronomers — Terror which comets
formerly inspired—Recent comets—Periodic comets—Changes to which
comets are liable, both in regard to their shape, motion, and course—
Their volume and mass—Possibility of a comet coming into contact with
the Earth—Result of the shock—Density of the various portions of a
comet—The passage of the Earth through the tail of a comet—Account of
the chief periodical comets—The comets of Halley, Encke, Biela or
Gambard, Faye, Brorsen, d’Arrest, Tuttle, and Winnecke.
I.
The etymology of tlie Greek word comet, is a hairy star•
The luminous point generally visible about the centre of a
comet is called the nucleus. The sort of luminous aureole
which encircles the nucleus is known as the hair of the
comet. The nucleus and the hair together form the head.
The luminous trains varying in length, which form part
of most comets, are known as the tails.
Nearly all these comets appear only in the shape of
vaporous masses, either round or slightly oval, denser to-
wards the centre, but without distinct masses or anything
that can be called a solid body.
The stars remain visible even when they are covered by
the apparently densest part of a comet, yet the lightest of
clouds conceals them from our view altogether. But in
certain comets a solid nucleus, extremely small, has been
observed by means of very powerful telescopes.
v290
ASTRONOMY.
The extraordinary volume of the comets is probably due
to the slight amount of attraction which the very diminutive
nucleus exercises upon the elasticity of the gaseous par-
ticles, the force of attraction being, as we know, in direct ratio
to the density of the mass, that is to say, that the more mole-
cules a body contains in the same volume, the more powerful
is its attraction upon the surrounding bodies. If the Earth
were to diminish in density, the atmosphere would at once
extend very much farther. The nature of the comets is still
an unsolved problem. At the same time it has been ascer-
tained that most of those which have been brought under
examination circulate around the Sun, like the planets, in
obedience to the laws of Kepler, but they describe very
eccentric ellipses, the planes of which instead of being
almost merged in the ecliptic, as is the case with the prin-
cipal planets, present an infinite variety of inclinations. The
comets change in aspect from day to day, and they cannot
well be identified from their appearances. Therefore, to
establish the identity of a comet at its various apparitions,
we must have recourse to mathematical calculations.
Most of the ancient philosophers looked upon comets
either as atmospheric meteors, or passing celestial pheno-
mena. Some of them held that they were, like the shoot-
ing stars, terrestrial exhalations which took fire in the
regions of flame; others considered them to be the souls of
illustrious men ascending to heaven. But Pythagoras
appears to have formed a fairly correct idea as to their
nature, for he maintained that they were actual stars moving
round the Sun, yet even he never suspected the elliptic
nature of their orbits. The first reliable demonstration of
the planetary motion does not date back beyond the close
of the 16th century.THE COMETS.
291
II.
Sir William Thomson, in his speech at the Edinburgh
meeting of the British Association in 1871, referring to the
present state of our knowledge on this subject, said:—
“ Great progress has been made of late years towards
the discovery of the nature of comets, and the truth of an
hypothesis which has long seemed plausible to my mind is
now almost certain; viz., that they consist of meteoric
stones. This supposition accounts satisfactorily for the
light of the nucleus, and furnishes a simple and rational
explanation of the tails of comets which have been regarded
even by the greatest astronomers as bordering upon the
super natural.’’
It is needless to remark that this opinion does not meet
with universal acceptance, and it furnished the subject of a
long debate in the French Academie des Sciences in the
following October. M. Faye, in his work on comets, and
what we at present know about them, says:—
“ Subsequent to the researches referred to in the first
portion of this work, two new facts have been brought to
light. Huggins has discovered in the spectrum of the
nucleus of certain comets, luminous rays which he attributes
to the incandescence of carbonised vapours. Upon the
other hand, the researches of Schiaparelli, Newton, Le
Verrier, Peters, Adams, and others, have shown that certain
periodical clusters of shooting stars are closely connected
with certain comets also periodical, for these clusters and
the corresponding comets follow exactly the same course in
the skjr. Tait has deduced from these two facts alone a
whole theory concerning the phenomen of comets. He
coincides with Sir W. Thomson in thinking that comets are292
ASTRONOMY,
mere aggregations of aerolites, the mutual encounters of
which would engender the light that Huggins has observed,
and that there are only a portion rendered visible for a brief
moment of the cluster of shooting stars which must accom-
pany every comet. This second supposition would upset all
the hitherto-received theories and observations, and I only
notice it to point out that if Schiaparelli’s discovery has, so to
speak, given us the key to the enigma of shooting stars, it is
quite silent as to the comets themselves. This is a question
of common origin very unexpectedly asked, and as wonder-
fully answered: the tails of the comets have nothing to do
with it. As to the first point in Mr. Tait’s hypothesis, it
seems very plausible, viz., that the light emitted by the
nucleus may be produced by the encounter of two comets.”
I must add that Delaunay in his Treatise upon the Pro-
gress of Astronomy considers the shooting. stars as small
comets, moving through space in clusters.
III.
In the early ages, comets, appearing only at rare intervals,
and being of a shape so different from the other stars,
created almost universal alarm. Their existence—apart, so
to speak, from the regular stars in the sidereal regions—the
singularity of their motions and their peculiar shape, ex-
plains this feeling of terror at a time when science had not
as yet laid bare the mysteries of the firmament. They were
looked upon as the presage of great calamities, and it was
said that the death of Julius Caesar was announced by the
comet which appeared in the year 14 n.c.; the cruelties of
Nero by that of a.d. 64, and the origin of Mahometanism
by the comet in 608, because its tail was in the form of aTHE COMETS.
293
scimitar. Tlie comet of 1240 was looked upon as the fore-
runner of Tamerlane’s invasion, and the fall of the Greek
empire to have been heralded by that of 1456. When the
comet of 837 appeared, Louis I., son of Charlemagne, who
dabbled in astronomy, looked upon it as the presage of his
death, and, sinking into a state of deep melancholy, did not
survive it more than two years. A comet, known as Halley’s
comet, appeared in 1066, when William the Conqueror in-
vaded England, and it was worked into the Bayeux tapestry
by Queen Matilda. The comet of 590 was held respon-
sible for a singular epidemic, which caused the death of
people by making them sneeze to excess.
M. Cabinet says: “ Seneca combated the superstitious
ideas of his predecessors and contemporaries, maintaining
that comets moved in fixed courses, and that posterity would
be unable to comprehend that so patent a truth had ever
been disputed.” The theoretical researches of Newton and
the calculations of Halley have verified the predictions of
Seneca, and the return of several comets, following as they
do, regular orbits, can be accurately foretold.
The comet of 1664 was expected by the vulgar to cause
the death of every European sovereign, but none of them
happened to die in that year, and so far from having caused
misfortunes, we have to thank them for several excellent
vintages, teste that of 1811.
IV.
There have been many remarkable comets of recent
years.
Upon the 8th of January. 1862, M. Winnecke of Poulkova
observed a telescopic comet from 3 to 4 minutes in diameter,294
ASTRONOMY.
and it subsequently transpired that the same comet had
been discovered by Mr. Tuttle in America, nine days
beforehand.
Another comet, visible to the naked eye for those who
had good sight, was seen on the 2nd of July at about 10 p.m.
by M. Schmidt, director of Baron Sina’s observatory at
Athens. This comet appeared quite suddenly, travelling in
the direction of the North Pole, and reminding one in the
manner of its arrival of the great comet of 1861 as it first
appeared in Europe. The latter, seven weeks before be-
coming visible upon our continent, had been clearly seen in
the southern hemisphere, by myself, amongst others, in the
Isle de la Reunion.
It was visible about 7.30 p.m. in the north-east, just about
the sea-line. It gave a faint light, not greater than that of
a star of the third magnitude, but on the other hand its crest,
pointing eastward, extended nearly 18° in length, even as
seen with the naked eye.
The comet of Charles V., expected from 1856 to 1862,
and which was expected to come in contact with the earth
and crush it to pieces, is now forgotten, and will not be
seen in our day. And when we remember the terror which
its advent caused, we can scarcely be allowed to despise the
credulity of our forefathers.
V.
Out of more than six hundred comets which have been
observed since the birth of Christ, the orbits of nearly one-
third have been calculated, but out of this number it is
impossible to predict with complete precision the return ofTHE COMETS.
295
more than eight or nine. But this subject will be treated
at greater length in the latter part of this chapter.
The other comets mostly accomplish their orbits in such
elongated ellipses, taking into consideration their greatest
dimensions, and the portions of orbits in which we perceive
them are so limited, that it is scarcely possible during a
single appearance to do more than ascertain the position of
the plane in which they move, and the length, as well as the
direction to the perihelion, that is to say, to their shortest
distance from the Sun.
It is only when the orbits of two comets which have
appeared at different epochs have almost the same elements
that astronomers consider themselves justified in considering
these comets as identical, and, consequently, in drawing a
conclusion as to the nature of the orbit and the length of
the revolution.
The physical appearances of these bodies undergoes so
many changes from day to day—and a priori between two
apparitions, years apart—that it is impossible to establish
their identity through a resemblance in shape.
Even a resemblance of elements can only be considered a
complete proof of identity when the reappearance which has
been surmised from this resemblance has actually taken
place. It is not until then that a comet is classed as
periodic, and that the elements of its orbit can be calculated
with precision.
In the case of a comet with a known rotation, an
astronomer can fix the day when it will be in its perihelion,
or nearest to the Sun, and the day when it will be nearest
to the Earth, but it is impossible to predict when the most
familiar of the comets will become visible to us, for observa-
tion has shown that their visibility is dependent not only296
ASTRONOMY.
upon distance, but on other physical circumstances to which
they may be influenced in their remote course, and which
we are utterly unable to calculate.
VI.
From the earliest ages of astronomy down to the invention
of the telescope, only the most brilliant comets could be
seen, but now scarcely a year passes without one or two
being observed.
A certain number of these bodies escape observation when
they traverse the sky at day-time, unless they should
coincide with some such rare occurrence as an eclipse of the
Sun. Seneca relates that this did happen in the year
60 b.c.
Others, again, so brilliant as to be visible at mid-day, as,
for instance, the comet in the year 44 b.c., and those of
1402 and 1532.
The comets describe such elongated ellipses round the
Sun that they seem to move almost in a straight line. The
position of these ellipses varies very much, as the comets
move in all directions.
As they vary much in their distance from the Sun they
undergo extreme alternations of heat and cold.
The comet of 1680 was, when at its perihelion, only
532,000 miles from the Sun, or more than 166 times nearer
to it than we are, and must therefore have received 28,000
times more heat than reaches the Earth, which is equiva-
lent to a temperature several thousand degrees above that
of molten iron. The comet of 1843 passed within 33,000
miles of the Sun, and must have had a temperature nine
million times greater than that of our globe.THE COMETS.
297
As a general rule, comets do not become visible to us
until they reach that part of its orbit nearest to the Sun.
Arriving there, the velocity of their course increases, and
they soon disappear from our gaze.
Their return, on the contrary, is often delayed by several
centuries, because as they recede farther from the Sun their
velocity, like that of the planets, becomes progressively
less.
The rapidity of the comet of 1682, as calculated by
Newton, was nearly 900,000 miles an hour, and it was
coming down from the most remote regions of the expanse
at a right angle to the Earth’s orbit.
VII.
In 1705 Halley, taking Newton’s system of attraction as
his basis, made calculations on the orbit of several comets.
He ascertained that the comets of 1581, 1607, and 1682,
were in reality one and the same, the next reappearance of
which would take place in 1759, and his prediction was
verified to the letter. This comet also appeared again, as
he had foretold it would, in 1885, and will not be visible
again until 1911. The great axis of its orbit is 8,200,000,000
miles, and its period about 76 years.
The first comet, after that of Halley, which was taken to
be periodic, was that of June, 1770, discovered by Messier.
This comet was ascertained by Lexell to have an orbit so
much curved that it enabled him to measure the ellipse, which
had a major axis not more than three times the diameter of the
terrestrial orbit. This would infer a revolution of not more
than five years and some months, yet this comet never
reappeared. Such a discrepancy naturally excited the298	ASTRONOMY.
attention of astronomers, and it was eventually found to be
due to planetary perturbations. In 1767, for instance, con-
tiguity to Jupiter had sufficed to convert an ellipse of
50 years and a perihelion of 500,000,000 miles into the
ellipse and perihelion as observed in 1770. In 1776 this
comet passed during the day-time, and while it was receding
afresh Jupiter affected the ellipse of 1770 to such an extent
that the comet was henceforth invisible to us, as its peri-
helion became 350,000,000 miles, and the length of its
revolution twenty years.
Messier discovered, besides this comet, sixteen others.
Delambre tells us that his love of astronomy was so great
that, on Montagne of Limoges observing a new comet just
as he had lost his wife, Messier exclaimed: “ I had dis-
covered eleven, and now Montagne has deprived me of my
twelfth.” Perceiving that his friends were alluding not to
the comet, but to his wife, he admitted that she was an
excellent woman, but Delambre adds, perhaps with a spice
of the malice which seems inherent in scientific natures,
that he was still harping on Montagne’s discovery.
Newtons comet has a period of about 575 jrears, and it
has been calculated, upon tracing it back, that it must have
passed near the Earth in the year 2349 b.c., the date at
which Moses puts the deluge, though this comet could not
have been the cause of it. Newton amply refutes the
system which has been attributed to this comet, which, at
its last appearance in 1680, came within 35,000 miles of
the Sun.
I must point out, however, that the predictions as to the
return of comets are not always absolutely accurate. Thus,
Halley’s comet reappeared in 1759, but some months behind
time, the delay, caused by the action of some neigh-THE COMETS.
299
bouring planets, having been foretold by Clairaut, who thus
triumphantly demonstrated the truth of the attraction
theory, which many of the savants had refused to accept.
The beautiful comet of 1556, calculated to return in
1848, has not reappeared. A Middelburg astronomer was at
infinite labour to calculate the secondary influence of the
planets upon the return of this comet, and he came to the
conclusion that it would be seen in 1858, but it failed to put
in an appearance, nor has it as yet been seen.
The comet of September, 1853, was 70,000,000 miles
from the Earth. It travelled at the rate of 400 miles a
minute, 24,000 an hour, and 576,000 a day. It was, in
diameter, about equal to the Earth; its tail was 4,000,000
miles in length, and about as broad as the space which
separates the Earth from the Moon, viz., 240,000 miles.
VIII.
It is not impossible for a comet to come into contact with
the Earth, but there are millions of probable reasons against
such an occurrence. Moreover, the ingenious mechanical
calculations of M. Babinet tend to prove that this shock
would affect us very slightly, owing to the trifling density of
the comet compared to the atmosphere. At the same time
it is only right to add that many other scientific men hold a
different opinion. The substance of M. Babinet’s two last
communications upon this subject to the French Academy
of Sciences, are as follows:—
Taking the calculations of Sir John Herschel, Struve,
Bessel, Admiral Smyth, and even Arago, the contrast of300
ASTRONOMY.
intensities induced him to believe that the atmospheric
equivalent of a comet was so trifling that he reduced the
density of those bodies almost to nothing; for it has been
impossible to discover any refraction even in their nucleus.
He also points out that the result arrived at is so marvellous
that he should have scarcely ventured to lay it before the
academy were it not directly deduced from facts and laws
universally accepted.
All astronomers have found that the density of the
comets is insufficient to shut out the light of the small
stars, whether it be the tail or the nucleus which comes
between them and us. Therefore, even if one of those
bodies should come into contact with the Earth, the matter
of which it is composed, almost devoid of density, would not
penetrate even the atmosphere of the globe. Stars of the
tenth, eleventh, and even of inferior magnitudes have been
visible through the central part of comets without suffering any
perceptible diminution of brightness. It is easy to explain
the error of those who have proclaimed the existence of an
opaque nucleus, and no better instance can be afforded for
proof than Encke’s well-known comet, which is sometimes
visible to the naked eye and which generally appears as a
round mass. In 1828 it formed a regular globe, nearly
320,000 miles in diameter, without any distinct nucleus,
and Struve was able to see through it a star of the eleventh
magnitude, which suffered no diminution of brilliancy.
It is a well-ascertained fact that moonlight blots out all
stars below the fourth magnitude : now there are six degrees
of stars between the fifth and eleventh magnitudes, and
according to the law of fractions by which these classes are
governed, it follows that a star which is one degree in size
greater than another is 2J times more luminous.THE COMETS.
301
It is concluded from this that a star of the fifth magnitude
is about 250 times more brilliant than one of the eleventh
magnitude, and that consequently the illumination ol the
atmosphere by the Moon is much more intense than the
illumination of the cometary substance by the Sun itseli,
inasmuch as a comet would need to be 3,600 times more
luminous than it now is to extinguish a star ot the eleventh
order, while the glow of the atmosphere at moonlight is
sufficient to render invisible stars 250 times more brilliant.
When we study the measurements ot Wollaston, against
which Sir John Herschel has nothing to say, the dispro-
portion becomes still greater, the illuminating power of the
full Moon appearing to be only 100^ that of the Sun at
noon.
M. Babinet, to complete his calculations, remarks that,
judging by the density of the air in the lower strata of the
atmosphere and its total weight as indicated by the column
of the barometer, the whole aerial stratum which constitutes
the atmosphere would not be more than five miles through
if its density was everywhere as great as the air upon the
surface of the Earth. He calculates that the substance oi
a comet has not a density greater than a 45 million
milliardth part (1 divided into fraction of 45 million
milliards) that of the atmosphere. The shock of so
rarefied a substance would not force any particle of the
comet into the most dilated parts of the extremity of our
atmosphere.
Slight as the cometary substance no doubt is, it is not so
to the extent that M. Babinet would make out, for, as I
shall relate presently, the Earth has actually passed through
the tail of one comet.soa
ASTRONOMY.
IX.
Accused of over estimating the want of density in the
substance of comets, he replied :
“I will quote the language of Sir John Herschel,
whose views must command general attention, and if his
opinion does not carry conviction with it, I may state that
I have in reserve two arguments which will prove that
comets do not contain enough substance to set up a
homoeopathic doctor. Sir John Herschel, in his work upon
the Excessive Tenuity of Comets, says : ‘ In fact, the tail of
a large comet might not weigh more than a few pounds, or
even ounces.’ This is very plain speaking (Outlines of
Astronomy, art. 359, 1850). In the Revue des Deux Mondes
I have given the weight of the Earth, and there is no need
to repeat it here, but the reader may rest assured that Sir
John Herschel’s comet is not larger, compared to the Earth,
than a fly w ould be compared to an elephant or a whale, and
even if its tail was of deadly poison it could not reach the
most ephemeral of created things upon the Earth. With-
out quoting the saying concerning the relative levity of
feathers, wind, dust, and wTomen, it may be safely asserted
that, whatever may be its truth, comets are lighter than
either of the above.”
X.
M. Arago says that the chances of an encounter between
the comet and the Earth are almost the same as those of
an encounter between twro atomic grains of dust, one of
wrhich is whirled into the air at Paris, and the other in the
United States. But M. Liais and several other astronomersTHE COMETS.
303
have since ascertained that the Earth and the Moon were
immersed in the tail of the Comet of 1861, and the pheno-
mena then observed strikingly confirm the conjectures of
those who maintained that the cometary substance could do
no harm.
And, as M. Liais, in his book, UEspace Celeste remarks,
our scientific attainments permit us to ascertain the ex-
tremely rarefied state of the gaseous medium which forms the
cometary appendages, and we conclude therefrom that even
if these gases are deleterious the quantity with which the
atmosphere would be impregnated would be too small to do
us any mischief.
Just before the encounter between the Earth and the tail
of the comet, M. Liais was enabled to take an observation
which, combined with those made before and after, allowed
ot his ascertaining as a positive fact that the passage of our
globe through the tail had really taken place.
It was not until after the passage that this comet “was
visible in Europe, where it was seen for the first time in the
evening of June 30th, 1861.
Two well known astronomers, M. Valz, of the Marseilles
observatory in France, and Mr. Hind, in England, also
remarked that the Earth must have passed through the tail
of the comet.
During the evening of June 30th, Mr. Hind and several
other observers in England had also noticed a sort of phos-
phorescence in the sky, with a yellow tint like that of an
Aurora Borealis, and they attributed it to the cometary
matter.
Baron de Prados, informed by M. Liais of what was
about to occur, observed the condition of the atmosphere at
Barbacene (Spain), and he remarked that the sky was very304
ASTRONOMY.
red all the time. This fact, taken in connection with what
was observed in England, deserves record.
Taken altogether, the details noticed upon this occasion,
show that the dangers apprehended, from an encounter be-
tween the Earth and a comet are purely imaginary.
M. Petit, of the Toulouse Observatory, referring to this
subject, says: “ In 1788 and 1831, the Earth was covered
for months together by mists, which were attributed to
the passage of cometary tails. Though many persons,
Arago amongst others, have declared this supposition to be
erroneous, it seems evident to me—and Arago himself has
admitted it in one of his works—that the planets must from
time to time absorb to themselves cosmical matter, and I
take this opportunity of citing a singular phenomenon
which was observed on the 13th of May, 1858, at Toulouse,
and other parts of the Haute-Garonne. I refer to a very
strong smell of chlorine, accompanying a marked decline of
light, from 2 to 7 p.m., just at the time, no doubt, when the
Earth was passing through a very slender part of the aste-
roid annulus, with which we come into contact at that epoch
of the year.” *
But uncertain as the course of comets appears to he, and
justified though we are in considering them as innocuous,
it is well to remember that He who has given order and sta-
bility to His creation, must have imposed upon them laws
which prevent the possibility of their causing confusion in
tlic universe.
* Petit’s Treatise on Astronomy, vol. ii. p. 197.THE COMETS.
305
XI.
M. Delaunay’s recent treatise upon the periodical comets,
which appeared in the annual publication of the Bureau des
Longitudes, furnishes me with some interesting information
concerning these bodies. I may mention that he does not
allude to Newton’s Comet, referred to above, probably be-
cause he does not consider the date of its return sufficiently
certain. We at present count eight comets which have be-
come visible from the Earth after their return had been
announced as probable.
1st. Halleys Comet, with a period of 76 years.—This
comet, with a longer interval between its apparitions than
any other, was discovered under very remarkable circum-
stances, which Lalande laid before the French Academy of
Sciences in 1759, at the time when the comet reappeared
in accordance with the prediction made by Halley fifty-four
years previously. The fulfilment of this prediction created
great satisfaction in the scientific world, and, referring to
the event, Lalande says:—
“ This occurrence, unparalleled of its kind, has changed
our surmises into certainties, and the Academy of Sciences
is delighted to announce the return of a comet, enabling us
to obtain for the future a multitude of fresh data and obser-
vations. Though for a long time astronomers have counted
upon the return of comets, though Newton asserted the
fact, and Halley fixed the certain date of one, the event did
not occur in their day. We, more fortunate, are able to
compare the facts related by history, and deduce from them
lessons for the future.”
Lalande also remarks that Cassini was the first astro-
nomer who attempted to calculate, by means of preceding30G
ASTRONOMY.
observations, the route taken by comets, and so to ascertain
the periods of their return, but he was only partially suc-
cessful, because the resemblances which he saw between
the comets observed by him were only apparent. The true
mode of comparison was, as Halley afterwards discovered.,
to contrast them with the Sun, and Lalande points out
that.* Halley, following the Newtonian theory, devised a
convenient method of studying a comet, the parabola of
which is known.* He first applied this method to those
comets with which he was relatively familiar, and gradually
extended it to those of which less was known, until, in
170.5, he had compiled a table of 24 comets, published in
the Philosophical Transactions, No. 297.
“ Comparing these 24 comets with each other, Halley
remarked that those of 1531, 1607, and 1682, had orbits
very similar to each other, and the resemblance, indeed,
seemed to him so striking that he expected this comet
would be seen again in 1758. To use his own words: * I
am very much inclined to think that the comet of 1531,
observed by Apianus, is identical with those which reap-
peared in 1607 (when it was described by Kepler and Longo-
montanus), and in 1682 (when I myself observed it). For
the elements of all three are the same, and the only marked
difference in them is in the time occupied by their periodic
revolution, and that may be due to various physical
causes. We have an almost similar instance of this in
Saturn, whose revolving motion is so affected by other
planets, Jupiter more particularly, that we can never fix to
a few days the duration of its periodic revolution. There-
fore the motion of a comet which travels four times the
distance of Saturn, would be all the more affected, espe-
Lifc of Halley. Astronomies Cumehcce Synopsis.THE COMETS.
807
cially as a trifling increase of its velocity may alter the
shape of its orbit, and change the curvature of its ellipse
to something like a parabola. I am confirmed in this view
by the conviction that this come.t is also identical with that
which appeared in 1456. It was seen during the summer
of that year following a retrograde course, and passing nearly
in the same direction between the Earth and the Sun. And
though no very precise observations were taken at that
time, I feel certain, from a comparison of its route and the
duration of its revolution, that it is the comet of 1581,
1607, and 1682, so that I can confidently predict its return
in 1758. If my prediction is fulfilled, it will be impossible
to doubt that the other comets also reappear in the same
way.’ ”
XII.
As the period of its reappearance drew near, great pre-
cautions were adopted for ensuring careful observations.
Clairaut conceived the idea of making a precise calculation
of the attraction which Jupiter had exercised upon this
comet when so close to it in 1681 and 1683, and he read a
paper at the Academy of Sciences (Nov. 14tli, 1758), of
which I subjoin a few passages:—
“ The comet which we have been expecting for over
a year has excited more than the usual amount of interest
amongst the public. The real lovers of science await its
return, as a striking confirmation of the truth of a system
which nearly all known phenomena render probable ; and I
undertake to show that the delay (the comet had been due
over twelve months), far from weakening the theory of
universal gravity, is a necessary complement of it. I will308
ASTRONOMY.
even say that the delay must be still greater, and I will
endeavour to assign its limits.”
He then goes on to explain what method Halley adopted
to take account of the inequality in the successive periods
of the comet, and that the latter roughly estimated its fresh
period at 76 years, placing its probable return in 1758 or
the early part of 1759.
The details appended to his prediction, though only par-
tially worked out, were a necessary part of it; but they
were omitted by those French astronomers who alluded to
his theory. Moreover, impatient to see whether the predic-
tion would be verified, people had almost forestalled the
allotted period by looking for the comet before it could
fairly be said to be due. Clairaut also noted the various
results at which he had arrived, and stated that the revolu-
tion of the comet, subsequent to its previous appearance in
1682, would be 618 days longer than it was between 1607
and 1682. And he also added: “ I consider that the comet
will be in its perihelion about the middle of next April,
though I make such a statement with no little diffidence, as
several trifling details, of which we cannot judge approxi-
matively, may effect an alteration of a month or so, as in
the calculation of preceding periods. Moreover, as I said
at the beginning of this paper, there are many unknown
causes which may act upon the comet; nor can I be certain
as to the absolute precision of my own calculations until
they have been verified by my confreres.”
XIII.
Lalande, referring to the same subject, says: u Clairaut
asked me to give his theory a month’s law, and at the ex-THE COMETS.
309
piration of that period the comet appeared, with an interval
of 586 days longer than at its previous appearance in 1682.
It was within 32 days of the extreme limit assigned to it,
but such a period is nothing in an interval of 150 years,
during which it had only been possible to take a few rough
observations for nine months. To this must he added the
possible effects of the attraction of the solar system, of
comets as to which we know nothing, of the resistance of
the ethereal matter, concerning which we can form no
opinion, and of other quantities necessarily omitted from
approximative calculations—all of which may conspire to
hasten or retard its appearance. ... A difference of
586 days between the revolutions of this said comet—a
difference which may be due to the disturbing forces of
Jupiter and Saturn—demonstrates even more strikingly
than we could venture to hope the great principle of attrac-
tion, and places this law amongst those fundamental truths
of physics which are as certain as the existence of the bodies
producing them.”
Upon the 23rd of December, 1758, the comet was per-
ceived by a Dresden peasant called Palitsli, who forestalled
all the astronomers. Thus Halley’s prediction was realised,
and the reappearance of the comet could be safely counted
upon 75 or 76 years afterwards, viz., in 1835. Punctual to
its appointed time, it was in its perihelion on the 16th of
November following, Damoiseau having calculated it for the
4th, and Pontecoulant for the 13th of that month. The
latter has calculated that it will be in its perihelion again
on the 24th of May, 1910.*
Tracing this comet back, science, with the help of history,
Academic dcs Sciences, vol. lviii.310
ASTRONOMY.
Las ascertained that it was observed in June, 1456, Novem-
ber, 1378, September and October, 1301, April and May,
1066, September, 989, March, 141, January, GO, and
October of the year 12 e.c.
XIV.
2nd. Enckcs Comet, with a period of 8 years 3 months.—
This comet was discovered in 1818 by Pons, at Marseilles,
and its elements calculated by Encke, the Gotha astronomer,
in 1819. Its periodicity, at first calculated at 3 years and
8 months, tends to become shorter, owing to the perturba-
tions to which it is exposed during its course through our
solar system.
Poisson, in a memoir read at the Academie des Sciences,
remarks: “ Judged by the rapidity of its successive revolu-
tions, this body might be considered a planet, but it is still
classed with the comets because of its diverse appearances,
and the fact of its not being visible to us at all points of its
orbit. In order to facilitate observations of it at its return
in 1822, M. Encke intended to compile a diary of its
behaviour on this occasion, but as during the greater part
of this revolution it was not very far off Jupiter, he was
compelled to keep account of the perturbations caused by
the action of the latter planet. And he found that the effect
of this action would be to augment on the next occasion,
by about nine days, the mean duration of the anomalistic
revolution, which had taken 1,204 days, between the years
1805 and 1819. He announced that, in 1822, the comet,
judging from its declinations, would only be visible in the
southern hemisphere, and the event proved him to bo
right.”*
* Annual publication of tlie Bureau des Longitudes, 1872.THE COMETS.
311
From 1822 to 1871, in which latter year it was last seen,
this comet has regularly appeared at intervals of about 1,200
days. (It is next due about the 15th of January, 1875.)
Upon the occasion of its recent passage it was observed by
M. Stephan, at Marseilles, who discovered at the same time
seven new nebul© (Acaddmie des Sciences, 2nd half of
1871).
Keeping as exact an account as possible of the perturba-
tions to which this comet is exposed from the planets, Encke
arrived at the conclusion that the period of its revolution
continues to shorten, a fact which would seem to indicate
the presence of a resisting medium. As M. Delaunay re-
marks, such a medium, causing a gradual diminution in the
comet’s velocity, would render it more sensitive to the
attraction of the Sun; its orbit would become smaller and
smaller, whence would result a progressive diminution in
the time which it takes to travel over this orbit.
XV.
3rd. The comet of Biela or Gambart, with a period of 6
years.—This comet was seen for the first time on the 27th
of February, 1826, by Biela, at Josephstadt, in Bohemia,
and by Gambart, ten days afterwards, at Marseilles.
Clausen and Gambart made separate calculations of its
elements, and ascertained the duration of its revolution, so
that we are now in a position to predict the date of its
reappearance.
This comet intersects the ecliptic upon which its orbit is
inclosed at 12° 34' only, so that it is very likely to come in
contact with the Earth. In 1832 it passed within 20,000
miles of the terrestrial orbit, but the Earth was then at a312
ASTRONOMY.
great distance from this point, which it did not reach till a
month afterwards. It has been calculated that at this
distance, supposing the mass of the comet to be equal to
that of the Earth, the obliquity of the ecliptic would be
modified, and the length of our year considerably increased.
And as we have not experienced any change, its mass cannot
bear comparison with that of our globe.
It was again seen in 1846, when it presented a very remark-
able phenomenon, being divided into two distinct comets,
which proceeded in a parallel course, gradually separating
from each other. It again appeared as a double comet in
1852, and its two halves had continued to progress, side by
side, receding from each other very slowly. M. d’Arrest
has calculated that on the 28th of September, 1846, the
nucleus of the one part was 1,624,375 miles distant from
that of the other.
This comet should have reappeared in the early part of
1866; but, though the conditions for observing it were very
favourable, it was not seen. It was again due in the autumn
of 1872.
A very remarkable fact, from the scientific point of view,
is, that the results of manifold observations point to the
probable transformation of this eagerly awaited comet into
a current of meteoric bodies. This is argued by Mr. Al.
Herschel in an article in the Mondes Scientifiques of De-
cember 12tli, 1872.
Father Secchi has also communicated to the French
Academy of Sciences the account of a brilliant shower of
shooting-stars observed at Rome on the night of November
27th. The maximum was at about 8.80 p.m., when they
were at the rate of 93 a minute. He says:—“ From half-
past seven to one in the morning we counted 13,892 meteors,THE COMETS.
313
but the actual number was much greater. The whole sky
was literally on fire, and it is worthy of remark that during
this phenomenon the Earth was in the node of the orbit of
Biela’s comet.” *
It seems, then, as if this comet had undergone disrup-
tion, and that this was the cause of the great abundance of
shooting-stars observed in the direction which it followed.
XYI.
4th. Faye's Comet, with a period, of 7J years.—This comet
was discovered at the Paris Observatory on the 22nd of
November, 1843, by the eminent astronomer whose name
it bears. Soon afterwards, M. Goldschmidt, a pupil of
Gauss, basing his computations upon observations made at
Paris and Altona, calculated its elements and predicted its
return in 1851. M. Le Verrier, taking into account the
perturbations to which it would be subject in the course
of its revolution, fixed the time of its passage in its peri-
helion within two days of April 3rd, 1851; and his views
were singularly correct, for, reappearing at the close of 1850,
it was in its perihelion at ten in the morning of April 2nd,
1851. It has since appeared three times—in 1858, 1865,
and 1873. Professor Moller, of Lund (Sweden), has pub-
lished the diary of this periodical comet on the occasion of
its recent appearance. It was in its perihelion on the 18th
of July, 1873, and gradually approached nearer to the Earth
until the 10th of January, 1874.
5th. Brorsen's Comet, with a period of 5| years, was dis-
covered by Brorsen at Kiel on February 24th, 1846. As
the period of its revolution was reckoned at about 5| years,
Academic des Sciences (2nd half of 1872).314
ASTRONOMY.
it was looked for in the autumn of 1851, but it was not
seen on that occasion. It was again observed on the 18th
of March, 1857, and must have again been in its perihelion
in 1862 and 1868; but it was only visible in the latter of
those years.
6th. D'Arrest's Comet, with a period of 6 years 4 months.—
This comet was discovered at Leipsic on the 27th of June,
1851, by the astronomer after whom it is named, and its
return was announced for the close of 1857. M. Yvon
Villarceau, having prepared the diary of its motions on this
occasion, ascertained that it would not be visible in our
hemisphere ; but he forwarded his calendar to several
observatories in the southern hemisphere, and Mr. M'Clear
obtained a good view of it at the Cape of Good Hope. It
should have been seen again in 1864; but its next appear-
ance was in 1870, when Herr Winnecke observed it at
Carlsrulie.
7th. Tuttle's Comet, period 13 years 8 months.—This comet
was discovered at Cambridge (U.S.) by Mr. Tuttle, on the
4th of January, 1858, and was again observed by M. Borrelly
at Marseilles on the night of the 12th-13th of October, 1871.
It was also seen upon that occasion by Messrs. Loewy and
Tisserand at Paris, and may therefore be counted as one
of the periodical comets. It has been ascertained to be
the second comet of 1790, discovered at Paris by Mechain.
As the interval between 1790 and 1858 comprises five revo-
lutions of the comet, it must have returned five times (in
1803, 1817, 1830, and 1844) without being seen, and it was
again due in 1871. Basing his computations upon these
facts and the calendar drawn up by Hind, M. Borrelly was
enabled to observe it in that year.
8th. Winneclce's Comet, ivith a period of 5 J years, was dis-THE COMETS.
315
covered at the Bonn Observatory on the 8th of March,
1858. Its parabolic elements bore a great resemblance to
those of the third comet in 1819, discovered by Pons at
Marseilles, and it was soon ascertained that they were one
and the same. Since 1819 it has made seven revolutions,
and it has again been seen after two fresh revolutions only
three days apart from their predicted date, as Winnecke
himself was enabled to announce in 1869. It was again due
in the course of 1871.
XVII.
I will conclude this chapter with M. Delaunay’s summary
of the knowledge which we at present possess about comets
generally. He says:—
“ Comets occupy, so to speak, an intermediate position,
belonging partly to the stellar, partly to the planetary
system. They are small and irresoluble nebulae which
travel in space, and which, coming within the sphere of
the Sun’s attraction, approach that body at an increasing
velocit}% revolve around it at a varying distance from its
surface, and again move off towards other regions of the
sky, losing their velocity as they recede. If the Sun were
not attended by planets, all the comets which we see would
move in conformity with the principles enunciated, except
in the rare event of a comet coming directly in the Sun’s
course, and being lost in its mass. The presence of the
planets which circulate round the Sun, and which the comets
skirt in their motion towards it, often leads to important
modifications in the course of these wandering nebulae. The
attraction exercised by a planet upon a comet which passes
close to it may effect a great change in the size and direction316
ASTRONOMY.
of the latter, making the comet’s orbit round the Sun very
different from what it was before. This orbit may become
elliptical, in which case the comet has a motion analogous
to that of the planets, being incorporated, so to speak, in
the solar system. It then becomes a periodical comet,
reappearing at regular intervals whenever it is near enough
at its perihelion to be visible from the Earth. But, just
as a comet coming from the depths of space may be made
periodical by the action of certain planets, so the motion
of a periodical comet may undergo such an entire change in
its passage near a planet, that it will cease to be periodical,
and recede indefinitely until it falls into the sphere of
attraction of some other sun. Thus we see how the nature
of comets varies.” *
Rapport mr les Progrls de VAstronomie, p. 32.CHAPTER XY.
SHOOTING-STARS, BOLIDES, METEORITES, ETC.
These phenomena alluded to by Homer, Ossian, Milton—Phenomena which
must not be confounded with each other—Meteorites and their sub-
divisions—Gaseous or pulverulent matters reaching the terrestrial atmo-
sphere from the planetary regions—Showers of Sahara sand observed
at a great distance from the desert—Apparitions, motion, number, shape,
composition, and weight of meteorites—History of principal meteorites—
Meteorites of the rivers iEgos-Potamos and Abydos—Cybele and the Sun
worshipped in the form of meteorites—Extraordinary bolides, as related
by Plutarch — Meteorites in the Paris Exhibition of 1867 — Modern
savants and the meteorites; the pertinacity of M. Cliladni—Shower of
aerolites in 1803, which were observed by M. Biot—Hypotheses sug-
gested in explanation of these phenomena—Are meteorites found in the
atmosphere ? — Are they asteroids or small planets ? — The Moon, a
troublesome neighbour—Analogy between meteorites and comets—Has
the Biela comet been transformed into meteorites ?—Periodical apparitions
—Radiant points — Periodic and sporadic shooting-stars — Days and
months when shooting-stars are most numerous—The influence of the
precession upon their apparition—Shooting-stars and the Chinese —
Meteoric currents—Shooting-stars subject to the general laws of the
universe.
I.
The name of shooting-star is given to bodies which seem
on fire, and move through the sky with enormous rapidity.
They are commonly called bolides, and also aerolites,
meteorites, &c.
It is evident that the brilliant phenomena of shooting-
stars have been known from the earliest times, as various
writers not only employ them in metaphors, but give an
accurate account of them, Homer, describing the descent318
ASTRONOMY.
of Minerva from the heights of Olympus, to break off the
L’uce between the Greeks ancl the Trojans, says:—“ Like
a star, shot by the son of crafty Saturn, as a warning to
sailors or to a great army, which glitters and darts forth
many scintillations, so did Minerva, speeding to tlie Earth,
throw herself into the arena.” *
Ossian makes the bereaved Fergus exclaim: “ And thou
too, Morna, loveliest of maidens, thou sleepest thy last
sleep on the hollow rock. Thou hast been precipitated
into the darkness like a shooting-star which is buried in
the deserts of the sky, and the passing light of which is
regretted by the solitary traveller.” t
Milton also, in the Fourth Book of “ Paradise Lost,”
compares Uriel to a shooting-star:—
“ Thither came Uriel, gliding through the even
On a sunbeam, swift as a shooting-star
In autumn thwarts the night, when vapours fir’d
Impress the air, and shews the mariner
From what point of his compass to beware
Impetuous winds.”
II.
Those who are not versed in the study of meteorology
are inclined to think that all shooting-stars are of this nature
and origin. It was to prevent any error of this land that,
when the denomination of bolide was given to a meteor
recently observed, M. Elie de Beaumont pointed out that,
in studying these phenomena, it is important not to forget
that a bolide, from the derivation of the word, is a sort of
natural projectile, and that about the year 1820 it became
apparent that most of the shooting-stars answered to this
* Iliad, Book iv.
t Ossiau, Book i.SHOOTING-,STARS, BOLIDES, METEORITES, ETC. 319
56. —Bolide in fusion observed over Athens.820
ASTRONOMY.
description. But, at the same time, there is nothing to
show that luminous points or discs of a different kind do
not from time to time appear in the sky. Before looking
upon the shooting-stars as being generally very small
planetary bodies, he would suggest an examination as to
whether they might not result from the conflagration of
masses of vapour condensed in certain parts of the atmo-
sphere. The existence of wills-o'-the-uisp, thunderbolts,
phosphorescent clouds, and other unknown apparitions of
the kind, proves how careful we must be in our denomina-
tion of these phenomena (Acadimie des Sciences, 1871).
Thus, we must not set down indiscriminately as bolides or
shooting-stars all the luminous and fugitive points which
traverse space, as is too often done.
III.
The bodies which reach our atmosphere from the planetary
region, and which are comprised in the generic term meteor-
ites, have been divided into two classes—the irons or meso-
siderites, and the stones or lithosiderites, though of late years
a third division, intermediate between the other two, that of
siderolites, has been introduced by certain astronomers.
It has also been ascertained that, accompanying the solid
masses, or at least having the same origin, certain gaseous
or pulverulent matters reach our atmosphere. In a memoir
by M. Baumhauer, presented to the Academie des Sciences
by M. Ch. Sainte-Claire Deville, there are some interesting
heads of information. He maintains that not only solid
bodies, but also mists of uncondensed matter, penetrate to
our atmosphere, and that, as the meteoric stones are par-
tially and the meteoric masses of iron almost entirelySHOOTING-STARS, BOLIDES, METEORITES, ETC. 331
composed of iron and nickel, sb it may be that the meteoric
mists also contain a considerable proportion of magnetic
metals. M. Baumliauer considers that the main cause of
aurorae boreales is the magnetic action of these mists upon
the Earth.
He goes on to say that there are grounds for believing
that the higher regions of the atmosphere contain metallic
particles, in proof of which he cites the case of hailstones
with a metallic nucleus, as observed by Eversman at Ster-
litamack, in Bussia. These stones contained sulphate of
iron crystals; while in some hailstones which fell at Majo
(Spain) on the 21st of June, 1821, M. Pictet discovered
iron. M. Baumhauer attaches special importance to the
hailstones picked up at Padua on the 26th of August, 1834,
which, of an ashy-gray colour, were found by Cozari to
consist of various-sized grains, the largest of which were
attracted by a loadstone, and were composed of iron and
nickel. He adds that the identity of this matter with that
composing aerolites is beyond doubt, and that M. Quetelet,
whose death in February last deprived Europe of one
of her greatest astronomers, has remarked that the epoch
when aurorae boreales are most frequent coincides with the
period of the asteroids. Without asserting that his theory
as to the aurorae boreales is positively true, he considers it
worth investigation.*
IV.
Tarry, in a letter to the Academie des Sciences (1st half
of 1872), concerning the periodicity of the atmospheric phe-
nomenon of sand-showers observed in the south of Europe,
* Academie des Sciences, 1872.
Y322
ASTRONOMY.
endeavours to prove that the three showers of December
26th, 1870, June 27th, 1871, and March 10th, 1872, were
due to cyclones which, after traversing the continent from
north-west to south-east, became subject to a retrograde
motion when they reached the tropical regions. The condi-
tions of these phenomena are now so well known that their
arrival can be predicted several days beforehand. In proof of
this, he adduces the warning which he issued on February
27th, 1872, to several of the observatories in the south of
Europe of a sand-shower which would take place in the early
part of March. It occurred, as he afterwards learnt from
Rome and Palermo, on the 10th and 11th of that month.
All seafaring men must have remarked that the sands from
the deserts are carried out a great distance to sea, and I
myself noticed, at two hundred leagues from the African
coast, some very fine dust of a reddish colour which had
remained attached to the sails of the vessel in which I was
a passenger.
M. Daubree, of the Academie des Sciences, confirmed
this fact in a memoir which he received from the French
Consul at Sainte-Croix, in Teneriffe, who forwarded with
it a sample of the sand, which fell like rain in the western
part of the archipelago of the Canary Islands on the 7th of
February, 1863. The vessels at anchor there were coated
with it, and the peak of Teneriffe, though covered with
snow, seemed of a yellow colour after the shower. The grains
of this sand were so fine as to be almost impalpable, and,
with this exception, it was exactly like the sand of Sahara,
notably that part of the desert near Biskra, its mineral
components being the same down to the very debris of shells
which are to be found all over the African desert. There
can be no doubt that it had, in fact, been blown there,SHOOTING-STARS, BOLIDES, METEORITES, ETC. 323
though Sahara is nearly 200 miles away, and it was probably
raised by a waterspout to a height of more than 12,000 feet
above the level of the sea, whence it would reach the zone
of the atmospheric counter-current.
I may add, in explanation, that the sand may be conveyed
upon the sails of a vessel without any violent winds, as the
deposit may be effected by the slightest possible breeze.
Moreover, we find an analogy to this phenomenon in the
ejaculation of volcanic ashes, as in the year 472 the ashes
of Vesuvius were projected as far as Constantinople, which
is 700 miles distant.
V.
At the same time, I am disinclined to believe that all
sorts of dust, especially the metallic atoms suspended in
the atmosphere, have a terrestrial origin; and I rather
agree with the views put forward by M. Daubree in his
notice on their classification in the French Museum of
Meteorites. He says: “Though solid meteorites alone
reach the surface of the soil, it is very probable that
gaseous or liquid matter accompanying the solids, or at
all events having a common origin, penetrate into the atmo-
sphere.” Our knowledge concerning these extra-terrestrial
fluids is, however, too limited to allow of our classifying
them together.
Moreover, amongst the solid meteorites, many have been
known to fall with the same accompaniment of light and
report, not in a coherent mass, like ordinary meteors, but
in the shape of dust. As these meteoric particles have not
been sufficiently examined and distinguished from the dust
proper to the Earth, and as their nature may also be324
ASTEONOMY.
modified through their combustion in the air, I am unwil-
ling to attempt any explanation of them,*
VI.
The speed of these meteors has been said to attain 36
miles a second, double that of the Earth’s motion round the
Sun.
Supposing that it is only half as much, even then it
would be greater than that of all the principal planets, the
Earth alone excepted.
There is, however, a diversity of opinion upon this sub-
ject, and M. Daubree tells us that the Orgueil meteorite
travelled at the rate of 15 miles a second, and that the
speed of others was half as much again.
It has been ascertained that if shooting-stars catch fire
in our atmosphere, they do not originate in it—that they
come from the regions beyond it, and their direction gene-
rally seems diametrically opposite to that of the Earth in
its orbit.
Their number is sometimes prodigious, and, during the
great shower of shooting-stars witnessed in America upon
the night of November 12-18, they succeeded each other
at such rapid intervals, that it was impossible to count
them, though the lowest estimate put them at hundreds of
thousands.
They were seen all along the east coast of America,
from the Gulf of Mexico to Halifax, from 9 p.m. until
sunrise, and, at some points, until 8 a.m.
During their course through space, the meteorites emit
numerous sparks and leave a brilliant train behind them.
They often disappear without causing any secondary pkeno-
Academie des Sciences (July 8th, 1872).SHOOTING-STARS, BOLIDES, METEORITES, ETC. 325
mena; but sometimes they are accompanied by detonations
as loud as the report of a cannon, which are in turn followed
by the whistling sound of a projectile cleaving the air. These
projectiles, as they in fact are, are nearly all identical both
in regard to their physical components and their size.
The results of several hundred analytic examinations go
to prove that meteorites do not contain any elementary sub-
stance foreign to our globe. The elements which they contain
number, so far as is at present known, twenty-two, and they
are, taking them in the order of their predominance, as fol-
lows : iron, magnesium, silicon, oxygen, nickel,cobalt, chromium,
manganese, titanium, tin, copper, aluminium,potassium,sodium,
calcium, arsenic, phosphorus, nitrogen, chlorine, carbon, and
hydrogen. It is very remarkable that the three bodies which
predominate in the general composition of these meteorites,
the iron, the silicon, and the oxygen, are those which
preponderate in our globe.* It is also worthy of notice that
the iron and the silicon are in a metallic state, which is not
the case with many of the mineral aggregations upon the
surface of the Earth.
As a general rule, the aerolites are of a very uniform
shape; their numerous angles are often rendered obtuse
by the process of fusion, and their surface is covered with
a kind of black metallic enamel which is rarely more than
a millimetre (*03937 of an inch) thick. At the moment of
their descent they are very hot, and they range in weight
from a few grains to several hundredweight. The aerolite
seen by Pallas in Siberia was estimated at nearly 1G cwt.,
and another that fell in Brazil, though not more than four
cubic feet, weighed 14 cwt. It is said that one found upon
DauLree's Etude rcccnts sur les Meteorites, p. 53326
ASTRONOMY.
the hanks of the Plata was nearly 14 tons weight. In the
neighbourhood of Orgueil (France) there was a fall of these
stones at about sixty different places, all within an oval
less than 18 miles long, and at Laigte some 3,000 fell within
an even smaller compass.
VII.
M. J. Schmidt made a very remarkable observation of a
bolide in a state of fusion composed of two main fragments
with a brilliant green tint. The larger of the two frag-
ments followed the other, but there was little difference in
their size; each of them had a red tail, with the limit
separating it from the other clearly defined; and they were
also succeeded by smaller luminous bodies (each with its
red trail) irregularly distributed like sparks along the extent
of the tail of the main meteor, which faded away to nothing
at about 1 degree above the horizon. At this latter point
it appeared to consist of four or five fragments dirty red in
hue (see fig. 56, p. 819).
Father Secchi gives an interesting account of a bolide
seen near Rome upon the morning of August 31st, 1872,
which bore great analogy to a comet. At about 5.15 a.m.
a globe of bright flame slightly tinged with red appeared
upon the S.S.W. horizon, travelling N.N.E. Moving slowly
at first, its velocity soon increased, and it left in its track
a luminous train like the smoke of a railway locomotive, or
of a cloud when illuminated by the Sun, which, however,
had not risen. When it reached its culminating point,
E.N.E. of Rome, the flame expanded to the shape of a
cone, round at its base, and, shedding a bright light, dis-
appeared, darting the while small streaks of fire. From
two to four minutes afterwards, according to the positionSHOOTING-STARS, BOLIDES, METEORITES, ETC. 827
of the observer, a detonation was heard loud enough to
shake many of the houses and break the glass in their
windows. The report, less sharp than that of a thunder-
clap, resembled rather the blasting of a mine or the explosion
of a powder-magazine. It was followed by a rolling sound
like that of file-firing when succeeded by two loud artillery
reports. Fragments of black ferruginous stones were after-
wards picked up. The observation of this bolide is a matter
of great importance, for it appears to have been seen in the
dark like a comet approaching the Earth, and at the moment
of its apparition it seemed almost as large as the Moon.*
Plutarch alludes to a very similar bolide which appeared
in his day. Lucullus was in command of the Roman army
against Mithridates, and “ the battle was about to begin,
when suddenly, without premonitory signs, the heavens
opened, and a large burning body, in the shape of a barrel
and in colour like incandescent silver, fell to the ground
between the two camps. The two armies, equally terrified
by this prodigy, separated without fighting. This pheno-
menon is said to have occurred at Otryges, in Phrygia.” t
A remarkable bolide was observed by M. Silbermann
upon the 11th of June, 1867, soon after sunset, travelling
E.N.E. at a gradually diminished velocity. When it reached
a certain point very distant from the zenith, it suddenly
vanished from sight, and farther on in the same trajectory,
at a distance between two and three times the diameter of
the Moon, the bolide manifested its presence by a sudden
explosion, accompanied by a brilliant green flash of light.
Analogous phenomena have often been remarked, one of
which is reproduced in Chromo-lithograph No. 9.
* Academic des Sciences (2nd half of 1872).
+ Plutarch’s Life of Lucullus.328
ASTRONOMY.
VIII.
Many meteorites were shown in the Paris Exhibition of
1867. The St. Petersburg Academy of Sciences sent a series
of cardboard models of the Eussian meteorites, including
that seen by Pallas, and afterwards presented them to the
Paris Museum of Natural History. The Madrid Academy of
Sciences also sent a meteorite of stony composition, which
fell in the province of Murcia in 1858, and which was
remarkable from the fact of its being in the shape of a square
parallelopiped. A metallic meteorite, with curious cavities
upon its surface, formed part of the Chilian collection, and
it also has been presented to the Paris Museum of Natural
History.*
Aerolites have been known in all ages. Anaxagoras sup-
posed that they fell from the Sun, which he looked upon
as itself an immense aerolite. In his day, a black stone,
as large as a chariot, fell near the river iEgospotamos, in
Thrace, and is the first of these phenomena mentioned in
history. This stone was still visible during the reign of
Vespasian. Others were afterwards found in the Abydos
Gymnasium, and at Canondria in Macedon. Pliny states
that he himself saw one fall in the country of the Vocontii
(Narbonnese Gaul). Cybele was worshipped by the Gala-
tians in the shape of a stone fallen from the sky, and at
Emesa in Syria the Sun was worshipped in the like form.
It is natural to inquire whence proceed these bodies which
from the most remote ages have fallen upon the surface of
the globe in such large numbers.
M. Daubree, in his monograph upon the meteorites already
JDaubree’s Report of the International Jury, Paris, 1867.SHOOTING-STARS, BOLIDES, METEORITES, ETC. 329
mentioned, remarks: “ When we reflect upon the quantity
which reach the Earth every year, the natural induction
would be that many fell during the enormous intervals of
time when the stratified soils were in process of formation at
the bottom of the ocean, where they would have lodged.
Yet the most minute research has failed to discover any
trace of such bodies.
“ This fact, remarkable though it seems, may perhaps be
explained (as the result of my recent experiments would
indicate) by the rapidity with which these stones disappear,
owing to their oxydation when exposed to the action of
water.” *
Upon my return from the Indian Ocean, a magnificent
bolide, the apparent diameter of which was nearly equal
to that of the Moon, fell near our vessel (see fig. 57).
M. Daubree has also pointed out that stones of a certain
volume often penetrate deep into the ground; for instance,
one of those picked up at Aumale (Algeria) was imbedded
more than a foot in a block of hard chalk. This shows
that many meteorites may become lost to view.
IX.
For a long time, philosophers, being unable to explain
the phenomenon of aerolites, refused to believe in their
existence. It was not until 1794 that a certain M. Chladni
ventured to adopt the popular view, superstitious as it was
then thought, and to prove that, unlike many other super-
stitions, it was not without foundation. And when, upon
the 26th of April, 1808, a shower of very remarkable stones
fell during daylight at Laigle, a small town in Normandy,
* Etude rtcente sur les Meteorites, p. 8.ASTLIOXOIIY,
•Tlic fall of a bolide at sea.SHOOTING-STARS, BOLIDES, METEORITES, ETC. 331
the Institute appointed a commission to visit the spot, and
their report left no doubt as to the reality of aerolites.
Biot was nominated b}r the Academie des Sciences to go
and study the nature of this phenomenon, which seemed of
such questionable authenticity even to this body, familiar
as it is with science, that many of the members were averse
to taking the matter up, for fear of compromising their
dignity. M. de Laplace, however, overruled their objec-
tions, and Biot’s researches showed that he was right.
The following hypotheses were put forward in explanation
of the phenomena :—1st. The aerolites were supposed to be,
like hail or rain, actual meteors formed in the atmosphere
by aggregation.
Single at first sight, this hypothesis eventually proved
untenable. As a matter of fact, the elements which con-
stitute aerolites are not found in the atmosphere; and,
moreover, these elements would have to exist there in a
gaseous state, and in quantities large enough to form masses
weighing several hundredweight or thousands of stones of
different sizes. If the aerolites formed in the atmosphere
they would be subject to the laws of gravity, and would fall
in a straight line, which is so far from being the case, that
they have a horizontal decline apparently more pronounced
than that of our planet in its motion round the Sun.
2nd. Laplace thought that the aerolites might originate
m eruptions of lunar volcanoes. Lichtemberg had already
declared that “ the Moon is a troublesome neighbour, wli«
salutes the Earth by throwing stones at it.” As the Moon
is not surrounded by a resisting atmosphere, it is possible
that a stone might be ejected by one of its volcanoes
with sufficient force to get beyond the sphere of lunar
attraction and reach that of the Earth’s attraction. This332
ASTRONOMY.
would occur if the stone was projected at a velocity 5\ times
greater than that of a cannon-ball.
This hypothesis explains the oblique direction which
the aerolites follow, for, once beyond the limit of lunar
attraction, the stone becomes a satellite of the Earth, and,
owing to the perturbations to which it is subject, finally
falls to the surface.
3rd. Chladni argued that the aerolites were fragments of
planets, or even themselves diminutive planets, which, cir-
culating in space, had entered the terrestrial atmosphere,
and, gradually being deprived of their velocity owing to the
resistance of the air, finally fell to the surface of the
Earth.
This hypothesis, which converts them into asteroids or
small planets, a name formerly bestowed upon Ceres, Pallas,
Juno, and Vesta, circulating in milliards round the Sun,
and only becoming visible to us when they penetrate our
atmosphere and are set on fire there, would explain most
of the circumstances which precede and accompany their
fall.
M. S. Meunier, who has devoted special attention to the
study of meteorites, after laying down the principles which
he has evolved, says: “ Putting all hypotheses on one side,
it appears that the meteorites are derived from some planet,
now in a state of disaggregation, of which they form the
debris*
X.
It is only very recently that astronomers have been so far
able to trace their true origin as to permit of their discarding
* Academic dcs Sciences (2nd half of 1870).SHOOTING-STARS, BOLIDES, METEORITES, ETC.
333
the ancient theories, which were merely based upon suppo-
sition. It has been found that the Earth rushes upon its
rapid course like a vast cannon-ball amidst moving clusters
and rings of bullets circulating everlastingly in fixed ellipses.
These rings are regular rivers without beginning or end,
which pour along their bed in celestial projectiles, inter-
secting at several points the invisible route which the Earth
follows round the Sun.
The Earth, in its passage through them, is struck by
thousands of the small planets which drop on to its surface,
and its attractive force drags a great number more of them
in its train, causing them to revolve around it for some
time, like so many imperceptible moons, until they, too,
fall to its surface in the shape of shooting-stars so-called.
These phenomena have an imposing character which is
calculated to excite awe in the minds of those who witness
them for the first time. But it is still more marvellous to
reflect that our knowledge of the laws which regulate the
planetary system enables us to fathom their origin and the
way in which they have been attracted to us.
The extraordinary discovery of two periodic comets,
in close connexion with the showers of shooting-stars in
August and November, has exhibited the question of meteors
in a new light. Astronomers generally agreed in considering
the shooting-stars as forming part of the continuous rings
or clusters of cosmieal matter which circulate around the
Sun, until M. Schiaparelli conceived the idea of ascertaining
the parabolic elements of the shower of August the 11th,
just as if it was a comet coming from the remote regions of
space. He concluded that the shower was unconnected with
the solar system; and M. Delaunay says that his researches,
for which he was awarded the Lalande medal, have openedASTRONOMY.
334
a new path which will lead astronomers to the discovery of
the most important facts concerning the constitution of the
universe. Soon afterwards, M. Le Verrier, computing the
retrograde motion of the November shooting-stars, arrived
at the same conclusions as M. Schiaparelli. Thus, they
both assert that shooting-stars originate in the disruption
of vast masses of cosmical matter which penetrate into our
system, and which afterwards undergo total disaggregation
under the disturbing action of the Sun or one of the large
planets. The result of this would be a dispersion of these
matters along the orbit described by the primitive centre of
gravity of the mass, a dispersion which would eventually
lead to the constitution of a regular ring.
XI.
Two discoveries, made almost simultaneously by Messrs.
Schiaparelli and Peters in regard to the two orbits alluded
to, created great surprise in the scientific world. A remark-
able coincidence was at once arrived at—for these orbits were
found to be in every particular identical with the orbits,
recently calculated by Oppolzer, of the great comet of 1862
and of the first comet of 1866. And it is inferred that these
two cosmical masses both contained a comet when they
penetrated into our system, comets which escaped the com-
plete disaggregation of the primitive masses w hile continuing
to describe the same orbit as the matter which had been
broken up into fragments. Chladni suspected, so early as
1819, that there was a connection between comets and
shooting-stars, and Mr. Newton demonstrated in 1866 the
great eccentricities of their knowm orbits; so Delaunay is
no doubt justified in asserting that “ shooting-stars mustSHOOTING-STARS, BOLIDES, METEORITES, ETC. 335
be henceforth classed as small comets moving through space
in clusters.” *
It may also be worth while to append a very strange fact
of recent occurrence. The observations of astronomers have
made it almost certain that Biela’s comet, which has been
so long expected to appear, has been transformed into a
current of meteoric bodies (see M. HerscheFs article in the
Mondes Scientifiqiies, December, 1872).
Father Secchi also mentions a brilliant apparition of
shopting-stars on the 27th of November, 1872, the whole
sky seeming to be on fire, while it was remarkable that
during the phenomenon the Earth was in the node of the
orbit of /the comet (2nd half of Academie des Sciences,
1872).
Biela or Gambart’s comet was known to have a period of
6f years, intersecting the ecliptic, to which its orbit has an
inclination of only 12 degrees 34, thereby rendering its
encounter with the Earth very possible. It should have
reappeared in the autumn of 1872, and, as I have said,
astronomers are inclined to believe that it has been broken
up into the extraordinary numbers of shooting-stars observed
in the direction where it would have appeared.
At the same time, our actual knowledge does not enable
us to draw any rigorous conclusion as to whether the
matter composing comets and the clusters of shooting-
stars is identical or different.
XII.
M. Le Verrier, in his communication to the Academie
des Sciences referred to above, says that Mr. Newton of
JRapport sur les Progres de VAstronomic, p. 36.336
ASTRONOMY
Newhaven (U.S.), alluding to the showers of shooting-stars
since a.d. 902, has fixed the duration of a period of the
November phenomenon at 33J years.
Tlie discontinuity of the phenomenon shows that it is not
due to the presence of a ring of asteroids encountered by
the Earth, but to the existence of a cluster of asteroids
moving in closely adjacent orbits, and intersecting the
ecliptic, about the 13th of November.
The cluster in question might be of a much older date
than our system, but there is reason to suppose that it is
of recent origin.
It is a striking fact that the November swarm reaches as
far as the orbit of Uranus, and even a little beyond it, all
the more so because these orbits intersect each other at a
point situated in the rear of the swarm’s passage to its
aphelion and above the plane of the ecliptic. Now, Uranus
and the swarm could not have been both at this point simul-
taneously—that is to say, close to the node of the orbit—
earlier than the year 126; but in the beginning of that year
the cluster might have been close to Uranus, when the
action of that planet would have probably forced it into the
orbit which it now occupies, just as Jupiter provided us
with the comet of 1770.
Thus all the observed phenomena may be explained by
the presence of a globular cluster, forced by Uranus in the
year 126 into the orbit assigned to the cluster in which
our November asteroids now originate. The periodic
stars of August 10th, which, as the phenomenon recurs
every year, must be emitted by a regular ring, also admit
of a similar explanation. The only difference is that the
phenomenon has lasted longer; the ring has had the
time to form, and does not lend itself to so completeSHOOTING-STARS, BOLIDES, METEORITES, ETC. 337
a study as the November shower, while the annual con-
tinuity of the phenomenon prevents us from calculating the
period very accurately.
The researches of Schiaparelli and Le Verrier serve,
however, to throw great light upon the theory of shooting-
stars, and place it beyond mere conjecture.
XIII.
M. Faye maintains that the meteoric rings of April,
August, and November, the periodicity of which does not
admit of doubt, are, like the terrestrial orbit, almost cir-
cular ; and that, besides these three great rings, there are
a vast number of asteroids disseminated in all directions,
which, in addition to being seen at the main periods of
shooting-stars, form the contingent of the shooting-stars
seen at other times of the year. It seems that the majority
of these stars are in the ecliptic region, and move in clusters.
The two main meteoric rings of August and November are
henceforward clearly characterised both in respect to their
secular stability, the position and motion of their nodes, the
date of their regular returns, and the maximum period between
their apparitions (Academie des Sciences, 2nd half of 1871).
M. Le Verrier, alluding to the apparition of the 12th-14th
November, says that the shower gradually lessens, and that
the part of the sky which it traverses is very irregularly
divided. Thus, on the 12th, 107 shooting-stars were seen
at Brest and not one at Toulon, though the weather was*
equally fine in both places. Upon the 13th the number
did not seem to increase at the western stations, but at the
Barcelonnette Normal School 284 were counted, and upon
the 14th, at the same place, 544. At Alexandria, Genoa,
z338
ASTRONOMY.
Milan, &c., when the sky became clear, a large number
were observed. Denza was of opinion that the meteoric
current passed off in the night of the 14th to the 15th, but
that the radiant point was perhaps a trifle displaced; to
which M. Le Verrier replied that there was no displacement
of the radiating point or focus from day to day, but that
there are several radiating points which predominate in
succession.*
Father Secchi in his account mentions that, from what
he observed of the shooting-stars on August 10th, 1827,
these stars must be derived from at least three different
points—one in the direction of Cassiopea, another in that
of Perseus, and the third from the constellation of Camelo-
pardalis (Academie des Sciences, 1869).
XIV.
Thus we have the sporadic shooting-stars which appear
all through the year in every imaginable direction at the
rate of 10 or 11 an hour, and the periodic shooting-stars
which have appeared in clusters about the 9th-llth of August
with great regularity since 1842. Lastly, there are the
periodic November stars, the maxima of which vary very
much from year to year.
It is unnecessary to take the precession into account for
a calculation of a few years; but, in tracing back the shooting-
stars during previous centuries, it must be included in the
reckoning. If the phenomenon of August 10th, for instance,
corresponds to the same point in the terrestrial orbit, its date
would diminish by a day in every period of 71f years, count-
ing back; so that 716 years ago the phenomenon must have
* Academic des Sciences (2nd half of 1871).SHOOTING-STARS, BOLIDES, METEORITES, ETC. 339
occurred about the 31st of July or ten days sooner. The
Chinese annals allude to an apparition on the 5th of August,
1451, while our calculations indicate that it should have
been the 4th. Thus, in the course of ages, the phenomenon
undergoes a change in date, being two weeks earlier every
thousand years, just like the arrival of the Earth at a fixed
point of the ecliptic. The only conclusion to be drawn from
this is, that the ring of asteroids intersects the terrestrial
orbit at an almost invariable point, which may be now
estimated as 318 degrees longitude, and that such has been
the case for the last thousand years. The varying intensity
recently observed in these phenomena does not militate
against this supposition; for, admitting the period of variation
to be 20 years, the phenomenon would be explained by the
unequal density of the ring combined with the difference
of between the time of its rotation and the length of
the year.
This is not so with the November swarm. The celebrated
showers of 1799 and 1833 certainly took place from the
12th to the 13th; but at other times they have varied
between the 26th of October and the 16th of November,
and have now almost totally disappeared.
XV.
Silbermann, of the College de France, has devoted special
attention to the shooting-stars and collateral phenomena,
and he attributes to their influence most of the important
meteorological occurrences. It is impossible for me to relate
at length the fruitful results of his researches, and I must
be content to note a few of the most important.
He remarks that, if the shooting-stars travel from E. to W.,
z 2340
ASTRONOMY.
the thermometer tends to rise, the barometer begins to fall,
and the compass remains stationary. If their course is from
W. to E., the thermometer has a tendency to fall, the
barometer to rise, and the compass remains stationary. If
they are travelling from N. to S., the thermometer and
barometer both remain stationary, and the compass has a
tendency to point eastward. When their direction is inter-
mediate to that of any of the points mentioned, the result
is relatively identical. When some shooting-stars are
moving from E. to W. and others from W. to E., the
compass does not undergo any deviation. The temperature
increases in proportion to the number of shooting-stars
travelling in a direction opposed to the rotation of the
Earth, for in that case their velocity is lessened by the
attracting force of the Earth, while, moving more slowly
through space, their own heat is increased. The number
of radiant points which have been hitherto computed is 95,
and they are indicated by the names of the constellations
from which they appear to radiate. Amongst the principal
ones are the Leonides and the Lyrides as represented in the
accompanying chromolithograph. The Leonides have been
observed on one or two occasions to be shaded with a faint
auroral tint. Amongst the Leonides are two bolides seen
by M. Silbermann soon after midnight on the 13th-14th
November, 1866. In a space of 60 degrees, they revolved
no less than eight times around each other.
M. Silbermann is of opinion that “the mass of the
Perseides is much larger than that of the Leonides, inas-
much as it was capable of producing the aurora borealis of
August, 1869, while the Leonides, though far more brilliant,
would not then have given rise to a very visible aurora.
Nevertheless, this might not have been the shower ofSHOOTING-STARS, BOLIDES, METEORITES, ETC* 341
sliooting-stars seen in November, 1866, for the colour of these
stars seemed to be the whiter in proportion to the altitude
of the sky through which they moved, while they were
yellow, orange, blue, red, and green, according as their
trajectory was nearer to the N.W., at from 20 to 30 degrees
above the horizon. These facts imply the existence of atmo-
spheric tides, which would be rendered visible by the rapid
ascent of vapour charged with electricity and its transfor-
mation into light.” *
It is needless to remark that all these facts relative to
ehooting-stars come within the law of universal gravity, of
which they serve to illustrate the truth*
XVI.
The most useful observations of sliooting-stars have been
taken by M. Coulvier Gravier and his son-in-law, M. Chapelas,
and their contributions to the Academie des Sciences would,
if put together, form several large volumes. Amongst
other communications from this source, is a paper by
M. Chapelas concerning the direction taken by shooting-
stars, based on observations, 39,771 in number, extending
over twenty years (1848-1868). His conclusion is that the
number of these meteors increases from spring to summer,
and diminishes from autumn to winter. If shooting-stars
are examined without regard to their apparent diameter,
it will be found that their mean direction is always southerly,
no matter at what epoch of the year. If their mean direc-
tion is calculated in accordance with their size and with the
two principal epochs of the year, a result will be arrived at
from which this important principle may be deduced, viz.,
* Academie des Sciences, Feb. 19th, 1872.342
ASTRONOMY.
that there are two kinds of meteoric currents—one the
direction of which is constant, another the direction of
which varies with the time of year; the first predominating
in the upper strata of the atmosphere, the second having
its centre of action in a region nearer to the Earth. And
he remarks, in conclusion, that the indubitable connection
between the atmospheric currents and the direction of
shooting-stars may lead to useful discoveries (AcacUmie
des Sciences, 2nd half of 1872).
Thus we see that the study of this branch of astronomy
is anything but complete. Still, we know enough to affirm
that the shooting-stars, in all their evolutions, are in har-
mony with the laws of the universe.CHAPTER XYI.
THE DIVISION OF TIME.
Division of time ; the day, week, and month—The year; that of the Egyptians
and of the Chaldseans—The Olympiads—The Roman year—Months added
by Numa—Curious passage from Plutarch; different lengths of the years
—The Julian year—The Gregorian calendar—Reckonings of the Sun and
Moon amongst the Mexicans—Russian and Greek dates—The solar cycle
—The lunar cycle or golden number—Period called Saws by the ancients
—The epacts—Composition of the calendar—The calendar and meridian
—The absolute time and the mean time—Precession of the equinoxes—
Great year, or the world’s year.
I.
The ancients based their division of time dp on the motions
of the most visible of the celestial bodies, such as the Sun
and the Moon.
The perpetual alternations of light and darkness caused
by the Earth’s rotation upon itself naturally determined the
length of that portion of time called day, The Athenians
regulated their horal system from sunset to sunset; the
Babylonians, from sunrise to sunrise; the Egyptian and
Boman priests, from midnight to midnight.
The apparent revolution of the Sun round the Earth in
the space of 865J days formed the measure of the year.
The motion of the Moon around the Earth gave the
duration of the month, which is almost the twelfth part of
the year.
The division of the week into seven days dates from the
very creation of the world.344
ASTRONOMY.
It is said in the Book of Genesis that God created the
world in six days, and rested upon the seventh (that is to
say, ceased to create); and God commanded that man should
keep it holy, in commemoration of the repose which suc-
ceeded the work of creation.
M. Am. Sedillot, referring to the Bible story of the world’s
creation, says that it led to the conception of dividing the
week into seven days. “ The Greeks and the Romans, with
whom seven was a sacred number, were acquainted, as Aulus
Gellius testifies, with this division of time, but they did not
employ it. The former counted by the tceek of ten days
(decades), and the latter, in addition to the calends, ides,
and nones, had their week of eight days (ogdoades).” *
Although the days spoken of in Genesis are not days in
our meaning of the word, but undetermined periods of time,
they nevertheless gave rise to the computation of the week
which has been common to all nations. As Monsignor
Meignan, in his excellent work on “ Le Monde et VHomme
primitif selon la Bible,” well says (page 12): “ The week of
seven days was in use-all over Asia, more especially in
Babylon. It was known to the Chinese, the Indians, and
the Arabs. The Egyptians, it is true, counted by the decade;
but they also were acquainted with our elementary division
of time; and Dion Cassius states that this basis of the
Roman calendar and the names of the planets applied to
the days by the Romans were borrowed from the Egyptians.
Tuch says that the week of seven days had its origin in a
primordial principle which is universally known from the
Ganges to the Nile. The legends of the Eastern peoples
are only to be explained upon the assumption of a sub-
stratum of facts common to the whole human race; but it
* Comptes rendus dc la Academie des Sciences, Dec. 9th, 1872.THE DIVISION OP TIME.
345
is also certain that this primordial principle has been con-
verted into a legend.
When the nations gave themselves up to idolatry, they
conferred the names of the seven planets then known to
their gods, consecrating Monday to the Moon, Tuesday to
Mars, Wednesday to Mercury, Thursday to Jupiter, Friday
to Venus, Saturday to Saturn, and Sunday to the Sun,
II.
The table indicating the division of time into days, weeks,
months, and years, was called the calendar, from the calends
which, with the Romans, fell upon the first day of each
month.
The form and the arrangement of the calendar were not
everywhere the same, and this has surrounded chronology
and history with many difficulties.
With the Egyptians, the civil year consisted of 365 days;
so that, taking no account of about six hours each year, the
commencement of their year came round before the Earth
had completed its revolution round the Sun, and so in course
of time it began in the different seasons.
The Chaldseans took account of these four days, so as to
make their year always begin at the same epoch; and this
is why they had three years of 365 days, followed by one of
366 (Leap Year). Thus, after four times 365 or 1460 years,
the Egyptians, losing a day every four years, in the solar
year were 365 days a-head of the Chaldseans—that is to say,
the year 1461 with them was only the year 1460 with the
Chaldaeans.
About 776 b.c., the Greeks began to count by olympiads,346
ASTRONOMY.
which was a period of four years named after the Olympic
Games with the celebration of which it coincided.
The Roman year, under Romulus, consisted of ten months,
of which March was the first, September the seventh, October
the eighth, November the ninth, December the tenth—from
the Latin words, septem, octo, novern, decem. Numa subse-
quently added the months of January and February, in refer-
ence to which addition Plutarch says: “ Numa also changed
the order of the months. March was the first of the year:
he made it the third, putting in its place January, which, in
the time of Romulus, was the eleventh. February, previously
the twelfth and last, became the second. It is, however,
generally believed that January and February were added
by Numa, and that before his time the Roman year had
only ten months, just as with some of the barbarians it has
only three, or as with the Greeks, where the Arcadian year
consists of four and the Arcananian year of six months. It
is said that the Egyptian year formerly consisted of one and
afterwards of four months. This is why that people, though
inhabiting a very modern country, seem to reach back so
far in history; they parade their infinite number of years,
because each month counts as one.” *
III.
From this epoch down to Julius Caesar the Roman calendar
gradually got into such confusion that the latter determined
to have it reconstructed; and, by the advice of Sosigenes,
an Egyptian astronomer, he instituted the Julian calendar
in 45 b.c.
As with the Chaldseans, an extra day was interpolated
* Plutarch’s Life of Numa,THE DIVISION OF TIME.
847
every four .years; and it was placed immediately after the
sixth day before the calends of March, so as to make it the
second sixth day (bis sexto, dies), whence we have the name
bissextile given to the Leap Years.
This correction was eventually insufficient; for, in count-
ing the year at 365J days, it was made 11 min. 9 sec. too
long. This mistake, imperceptible for a short time, pro-
duced a day too many every 134 years; so that by the year
1582 the spring equinox, which should have fallen on the
20th of March, came ten days earlier.
Pope Gregory XIII., to make the equinox come right,
decreed the suppression of ten days; so that the day after
the 4th of October that year was counted as the 15th.
It was also determined for the future to strike out three
bissextile years every five centuries. Thus the years 1700
and 1800 were not bissextile, nor will 1900 be; but the year
2000 will be counted as bissextile. The Gregorian reform
of the calendar was everywhere adopted, except by the
Eussians and Greeks, who adhere, even in the present time,
to the Julian calendar, which explains why their year is
twelve days behind ours. Thus, in writing to Eussia, a
letter is headed with the double date, as 8th/20th of July,
which signifies that the 20th of July in England is the same
as the 8th of July in Eussia.
The Mexicans, for a people which were, so to speak, bar-
barian, possessed considerable astronomical knowledge, which
they made use of for the purposes of their civil and religious
life. They regulated the order of their two calendars, one
of which, literally translated, means reckoning of the Sun,
i
and the other reckoning of the Moon. The solar year was
composed of 365 days, divided into 18 months of 20 days,
plus 5 complementary days added on to the last month. Jt348
ASTRONOMY.
was represented in their paintings by a circle, in the centre
of which was a figure of the Moon lighted by the Sun, and
around it emblems of the 18 months (see fig. 58). In 1790
Fig. 58.—The Mexican year.
there was discovered amongst the foundations of Teocalli
an enormous piece of trappean porphyry of a dark-grey colour
and about 18 ft. in diameter, with a weight of 24,000 kilo-
grahnnes. It was covered with Mexican inscriptions relative
to the religious feasts and the days when the sun was at its
zenith. This relic has been well described by Humboldt
as a Mexican calendar (see fig. 59, p.351), and it has served to
clear up several doubtful points, and to afford the present349
THE DIVISION OF TIME.
astronomers of that country some insight into the theories
of their ancestors.
IV.
The solar cycle is a period of 28 years, at the end of which
Sunday and the other days of the week recur in the same
order and upon the same days of the month, because at the
expiration of this tune the Sun is nearly in the same sign
and in the same degree of the ecliptic as it occupied 28 years
before.
If the year was precisely composed of a certain number
of weeks, the same dates of each month would continue to
fall upon the same days of the week; but as the ordinary
years comprise 52 weeks and 1 day, and the bissextile years
52 weeks and 2 days, it follows that no year begins or ter-
minates with the same days of the week as the preceding
one, and that, consequently, the same days of the week*
cannot fall upon the same dates of the month in two con-
secutive years.
But, after 28 years, the day in excess of 52 weeks in
ordinary years, and the two days in excess of 52 weeks in
bissextile years, make up a period of five weeks, when, as
the 28th year is composed of an unfractional number of
weeks, it follows that at the expiration of this period the
years have the same days upon the same dates of the month.
The golden number, or lunar cycle, is a period of 19 years,
at the expiration of which the lunations recur upon the same
days of the month, and almost at the same hours. This is
because 19 years, or 228 of our solar months, are within a
fraction equal to 235 lunations. This period has been in
usage since the most remote ages, and was termed Saros by
the ancients (see Chapter I.).350
ASTRONOMY.
These 19 years are indicated by the numbers 1, 2, 3, &c.,
up to 19, when they begin afresh. For instance, the golden
number of 1865 being 4, this means that 4 years have
elapsed since the recommencement of the ‘lunar cycle.
This period was named the golden number, because, on
its discovery by Meton, the Athenians were so pleased that
they decreed that the calculation should be exhibited in letters
of gold in the public resorts, for the use of the inhabitants.
It has, however, since been ascertained that the new moons
do not recur exactly at the same hour every 19 years, as
Meton supposed. The difference is about 1J hours, which
gives 1 day 30 minutes every 312 years. This is why it has
been necessary to give up using the golden number, and to
substitute the epacts (from the Greek, to add on) for ascer-
taining with precision the Moon’s age.
V,
The epact is the age of the last Moon in a year at the
beginning of the following year.
Thus, the nuinb^^nscribed in the almanacs after the
word epact indica^/jffl^^thber of days which have expired
since the last newM^Wdne year up to the 1st of January
in the next year. / '>
For instance, in 1852 the epact is 9, which shows that
the last Moon of 1851 was 9 days old upon the 1st of January,
1852, and, consequently, that the new Moon began on the
21st of December previous.
As the epact is owing to the excess of the solar over the
lunar year, to calculate it * for any given year it is merely
necessary to know the amount of excess* viz., 11 days.
To take an instance, in 1843 the solar and lunar yearsTHE DIVISION OF TIME.
351
coincided, so the epact of this year was 0. In 1844 the
epact was 11, representing the excess of the solar year.
In 1845 it was 22, or twice 11. In 1846 it was 38, or
three times 11; but as the epact never exceeds 30, because
30 days make a month, 30, or an intercalated month, was
subtracted from the number 33. This subtracted month
was added to the year 1846, which was thus composed of
13 lunations, and the number 3 remained as the epact of
1846.
It is not very difficult to compile a calendar, for the main
point consists in finding upon what day of the month Easter
Fig; 59.-—The Mexican Calendar.
falls. This once ascertained! the movable feasts can be
grouped around it in their order.352
ASTRONOMY.
In a.d. 325 the Council of Nice ordered that Easter should
be observed upon the first Sunday after the full Moon which
follows the vernal equinox—that is to say, the full Moon
which falls on or after the 21st of March.
To find this Sunday, we must trace, by means of the
epact, upon what day of the month the new Moon of March
will occur, and add to this date 14 days, which will give the
day of the full Moon. If this day falls on or after the 21st,
Easter will be on the following Sunday; but if the full Moon
is before the 21st, then Easter will not be till the Sunday
after the next full Moon.
This is why Easter varies from the 22nd of March, as it
fell in 1848, to the 25th of April, as it will fall in 1886.
VI.
A somewhat important point will not be out of place
here. M. J. Bertrand, a member of the French Academy
of Sciences, put the following question to M. Jules Verne,
the well-known traveller and writer:—
“ A person starts from Paris on Thursday at noon, and
proceeds to Brest, New York, San Francisco, Yeddo, &c.
He returns to Paris after a journey of 24 hours at the rate of
15 degrees an hour. At each station he asks the time, and
the invariable reply is, ‘ Noon/ He next asks the day of
the week, and the uniform answer is, * Thursday/ until he
gets back to within a few miles of Paris, when he is told
that it is Friday. Where does the transition take placet
It must clearly be sudden. It will occur at sea, or in
countries which do not know the names of the days in the
week.
“ But suppose a whole parallel upon the continentTHE DIVISION OF TIME.
353
inhabited by civilised people, all speaking the same language
and subject to the same laws, there will be two neighbours,
one of whom will cry over the fence that separates their
dwellings, ‘ It is now noon on Thursday,’ while the other
will answer, * No, this is Friday.’
“ But supposing them, on the other hand, to live in two
adjoining villages near London, they will he agreed as to
the dates in the calendar. Thus the puzzle would he at an
end for the time; but it will spring up again in other places,
and there will be no end to the changes in the dictionary ot
the days of the week.” ,
M. Verne’s reply wras : “ It is true that going round the
world travelling eastward a day is lost, and that going round
the wrorld travelling westward a day is gained—that is to
say, the 24 hours occupied by the Sun in its apparent
motion round the Earth. This result is so well ascertained,
that the navy supplies the vessels going from Europe round
the Cape of Good Hope wTith an extra day’s rations, and
gives one less to those which double Cape Horn. It is
true also that, if there existed, a parallel traversing regions
all parts of which were inhabited, the inhabitants would
be quite at variance in their reckonings. But such a parallel
does not exist; nature has separated the chief nations by
deserts and oceans. The transition from the day gained to
that lost is effected imperceptibly. By an international con-
vention, the arrangement of the corresponding days takes
place at Manilla.* Captains of vessels alter the date in
their log-book as they pass the eighteenth meridian.” f
* This holds good of Paris, not London.
f Les Mondes Scientifiques, May 29th, 1873.
A A354
ASTRONOMY.
VII.
The absolute time is that which is measured by the daily
motion of the Sun; its duration varies because the march
of the Sun, or at least of the Earth, is unequal, alternately
accelerated or slackened according as it apxn’oaches or recedes
from the Sun. The mean or equal time is that measured by
the mean speed of the Earth, or by an uniform motion, such
as that of a clock. It is calculated upon the supposition
that at the end of every twenty-four hours the Sun is exactly
in the same meridian as it was the previous day. There
are only four days in the year when the mean and the abso-
lute time coincide—April 15th, June 15th, September 1st,
and October 25th. The maximum minus difference is 18"’ 6;
the maximum plus difference reaches 30"; but the balance
is exactly equal at the end of the year, leaving out of con-
sideration the planetary equations and the trifling secular
variations.
The precession of the equinoxes is the imperceptible motion
by which the equinoctial points are constantly shifting their
position upon the ecliptic, moving westward, in an opposite
direction to the order of the signs, so that the equinoxes
arrive every year 20' 25" before the Earth is in conjunction
with the Sun and the same star as in the same equinox
of the previous year. This difference is the cause of the
Sun's seeming to recede in the signs of the zodiac 1° in
72 years, and a whole sign or 30° in 2,156 years. Thus
the Sun travels over the whole circle of the ecliptic in about
26,000 years. Since the constellations of the zodiac have
received their names, the Sun has retrograded a whole sign,
and though we still speak of its entering Aries in the monthTHE DIVISION OF TIME.
355
of March, we ought to substitute Pisces, and so with the
other signs. The precession results from the unequal
attraction which the Sun and the Moon exercise upon the
various parts of the Earth, owing to its depression at the
poles. Hipparchus first observed this phenomenon, which
was explained by Newton.
The ancients designated under the name of great year a
very long period, at the expiration of vdiicli all the planetary
phenomena were supposed to recur in the same order and
at the same epochs.
The astrologers declared that the occurrences on the
Earth were connected with the celestial phenomena; so that
it was thought of the first importance to define wTith pre-
cision the great year, all the historic events of wliich were
to be reproduced ad infinitum. If such really had been the
case, the history of one great year would have been the
history of all future time.
Arago states that the chief ideas of the ancients con-
cerning this period and its duration as estimated by various
authors are as follows :—
The great year, also called the perfect year, the year of the
world, wTas the time taken by the seven planets known to the
ancients to return to the same relative positions.
Berosus says that the great year begins when the centres
of the seven planets are in a straight line with each
other.
Assimilating the great year to the ordinary years of civil
life, Aristotle believed that the winter of this period corre-
sponded to an universal deluge, and the summer to a general
conflagration.
Berosus, on the other hand, maintained that winter set
in when the line passing through the centre of the seven
A A 2356
ASTRONOMY,
planets penetrated Capricorn, and summer when this same
line passed through Cancer.
It does not seem as if the ancients were of one accord
as to the nature of the phenomena leading up to the great
year, some of them maintaining that there would be universal
conflagrations, others universal inundations.
As to the duration of the year of the world, some authors
estimate it at 6,670,000 years, while others, less venture-
some, refuse to fix any exact time, believing that to be
known to God alone. Cicero and Hesiod are amongst the
latter, and Arago cites the following passage, from Hesiod:—
The duration of human life is................... 96 years.
The rook lives 9 times longer than man, or	.	.	864	„
The stag, 4 times longer than the rook, or .	.	.	3,456	„
The crow, 3 times longer than the stag, or	.	.	.	10,368	,,
The phoenix, 9 times longer than the crow, or	.	.	93,312	„
The hamadryade, ten times longer than the phoenix, or.	933,120	,,
Thus the great year was a period entirely based upon
astrological creeds, varying wTith the particular ideas of each
astrologer. It exercised a great influence upon astronomy,
compelling those who were desirous of ascertaining its
duration to study with care the revolutions of the planets;
and in this way it led to an advancement of science the
progress of which ultimately destroyed the prestige of the
astrologers.CHAPTER XVII.
ASTROLOGY.
Dogmas ef the astrologers—Curious facts—Natural astrology—Judicial astro-
logy — Hippocrates — Yirgil —Horace—Juvenal—Plutarch—Tacitus —
Tiberius and Thrasyllus -— Astrology in Mexico — Montezuma and the
astrologers—Marsilius Ficinius—Pensa—Doctrines of the astrologers—
Albert the Great—Thurneiscn—Catherine de Medicis-Sensible advice
given by Horace.
i.
Nothing is more curious to study than the origin of the
various arts and sciences. It is astonishing to note the
errors and prejudices even of the most strong-minded and
talented of those who have begun to break fresh ground,
and this should serve as a warning to pedants who believe
that they are infallible. Astrology is derived from the Greek
words aaTpov, star, and Aoyos, discourse. It is a science
which consisted in reading or pretending to read the future
in the stars. Astrology, therefore, had its origin in astronomy,
which is, to use Kepler’s expression, the well-conducted
mother of a misbehaved daughter.
Both of these sciences were called into service by the
professors of the healing art; and M. Franck, of the Insti-
tute, in a treatise upon mysticism and alchemy, remarks:
“ There can be no wonder that Paracelsus was less successful
when he endeavoured to turn astronomy to the purposes of
medicine, for while it is true, as a general principle, that all
parts of the universe are connected with and react upon each
other, it is impossible to define these connections, or to358
ASTRONOMY.
make any use of them, when they do not full within direct
observation or the laws of computation.” *
There were two lands of astrology: 1st, natural astrology,
the object of which was to predict the return of the planets,
the eclipses, the tides and the changes of time, the tempests,
droughts, and inundations, as inferred from the data of
astronomy; 2nd, judicial astrology, by which, as it was pre-
tended, the destinies of individuals and nations could he
foretold through the stars and their aspects. To the latter
alone the word astrology, in its modern and derogatory
sense, is applicable.
Most w riters assert that this mysterious science originated
in Chaldsea, whence it penetrated to Egypt, Greece, and
Italy; others, again, attributed the invention of it to Shem,
the son of Noah.
Herodotus relates that the Egyptians set the practice of
dedicating each of the days and the months to some par-
ticular god, and that they were the first to judge of what a
man’s life wrould be by the constellation under which he
w^as born.
II.
It was believed that the stars regulated the life and
destiny of mankind, that each planet or constellation guided
either to good or evil the being created under it, and that
an astrologer, therefore, had only to know the hour and
minute of any person’s birth to determine the temperament,
faculties, destiny, illnesses, and manner and even the date
of his death.
Such vTas the belief, not only of the multitude, but even
* Philosophic ct Religion, p. 79.ASTROLOGY.
359
of those whose position and intelligence might have been
expected to raise them above such prejudices.
Nearly all the ancients, including such men as Hippo-
crates, Virgil, and Horace, were believers in astrology.
Belus, King of Babylon, says: “ I have read in the register
of heaven all that will happen to you and your sons.”
Juvenal writes: “The sign under which you are born is
a very important one. Fortune may convert you from a
spouter into a consul, from a consul into a spouter. What
do such men as Ventidius or Tullius prove, unless it be the
wondrous influence of a mysterious destiny, which at its
pleasure raises a slave to a throne, a captive to a triumphal
car? But so fortunate a man is rarer than a white crow.” *
In the time of Varro, the contemporary of Cicero, and
one of the most learned scholars of the day, there lived
one Tarutius, a philosopher and mathematician who took a
pleasure in dabbling in horoscopes, which he was reputed
to observe with great skill.
Varro invited him to determine the day of the birth of
Romulus, by a process of reasoning deduced from the known
actions of his life, as is done in the solution of geometrical
problems. The same theory which, with a given birth, fore-
casts a man's life, should, he said, be able, with a given life,
to discover the moment of his birth.
Plutarch, in his Life of Romulus, tells us that “ Tarutius
complied with Varro’s request. After making a very careful
study and comparison of both the adventures of Romulus,
the duration of his life, the manner of his death, and the
rest, he unhesitatingly announced that Romulus was con-
ceived in the first year of the second Ofympiad, upon the
23rd of the Egyptian month Choeac, at the third hour of
* Juvenal, Satire vii.860
ASTRONOMY.
the day, during a total eclipse of the Sun; and he added
that Romulus was born on the 21st of the month Thoth,
about sunrise, and that he founded Rome upon the 9th of
the month Pharmonthi, between the second and third hour.’
Fig. CO.—The Parcae, or Fates, and Prometheus, after an ancient bas-relief.
. . . “It is, in fact,” Plutarch goes on to say, “tlieopinion
of mathematicians that the fortunes of a city, like those of
an individual, have their appointed times, which are governed
by the position of the stars at the first instant of its founda-
tion.” But, as Plutarch indicates in a subsequent passage,
the belief in astrology was not universal in those days.
III.
Tacitus mentions that Tiberius had a great fondness for
astrology. He says: “ I must not omit to mention a pre-
diction which Tiberius made concerning Servius Galba, then
consul, whom he had summoned to Capreae. After sounding
him on various subjects, he added in Greek: c And thou too,
Galba, wilt one day taste the sweets of empire/ thus fore-
telling the latter’s long-delayed and ephemeral reign. HeASTROLOGY,
861
had learnt astrology at Rhodes from Thrasyllus, whose skill
lie had put to the following test:—When Tiberius consulted
an astrologer, he repaired to the highest storey in his palace,
and took as his only confidant an ignorant but lusty freed-
man, who conducted by steep and precipitous paths (the
palace being perched upon a rock) the man whose skill Caesar
desired to test. On his return, the freedman was to have
precipitated him into the sea, if he had been suspected of
indiscretion or trickery. Thrasyllus, conducted in this way
to the palace, had impressed Tiberius by his replies, and by
his disclosing to the latter prospects of future empire. Caesar
asked him if he had drawn his own horoscope, and what sign
he was then under. Thrasyllus then proceeded to examine
the position and the distance of the stars, which done, he
hesitated, and, after a second stiuty, began to tremble, ex-
claiming : ‘ The day is evil, my last hour is at hand.’ Tiberius
thereupon embraced him, and, felicitating him upon haying
escaped a danger by foreseeing it, accepted all his predic-
tions as oracles, and admitted him into the number of his
most intimate friends.” *
When Tiberius decided to leave Rome for Campania, the
astrologers made various forecasts relative to the journey.
“ Those who were able to read in the sky said that at the
moment of Caesar’s leaving Rome the position of the stars
indicated that he would never return there; and this was
fatal to many of them; for, in drawing the horoscope and
predicting from it his early decease, they had no conception
of his singular determination, and of the voluntary exile
which was to keep him eleven years absent. This showed
liow indefinite is the limit which separates truth from false-
hood and light from darkness. In their announcement
* Tacitus, The Annals, Book vi.862
ASTRONOMY.
that Tiberius would never re-enter Rome the astrologers
were right; but in all other respects they were wrong, for
he lived to an extreme old age.*
Astrology was in great repute amongst the Mexicans, and
every event was influenced by the hieroglyphics of the day,
demi-decade, or year. Hence the conception of coupling
together the signs, and of creating those purely fantastic
bodies which we find so frequently repeated in the astro-
logical paintings extant, of which a rough idea may be
gathered from figs.>59, 60, and 61, representing the calendar,
the year, and the signs of their days.
										ms?
		df|§				Sfif;			<w	
										US
					/	3l				
Fig. 61.—Signs of the days in the Mexican Calendar.
The apparition of a comet in the beginning of the six-
teenth century created great consternation in Mexico, the
multitude looking upon it as a presage of coming disaster.
The enemies of Montezuma, who was then on the throne,
said that*it was a forerunner of his fall; and, to dispel such
alarm, which he felt might be dangerous, the emperor
ordered his astrologer to explain the origin of this appa-
rition. The latter, who knew no more about it than the
rest of his compatriots, interpreted it in the same sense,
and was of course, as usual in those days, put to death.
* Tacitus, The Annals, Book iv.ASTROLOGY.
363
It is astonishing to remark with what obstinacy the ideas
of the astrologers were adhered to, no matter how often
they proved false. The bishops and other ecclesiastics of
the highest rank, the most celebrated philosophers and
doctors of medicine, drew the horoscope, and lectures were
delivered upon this subject at the university courses.
Marsilius Ficinus, in his “ Treatise upon the Prolonga-
tion of Life,” which was published during the last century,
recommends all prudent persons to consult an astrologer
every seven years, so as to be warned against the dangers
to which they might be subject during the coming seven,
and above all to esteem and make use of the remedies of the
Three Kings—gold, myrrh, and frankincense. M. Pensa
dedicated, in 1720, to the Council of Leipsic, a book entitled
“ De Propaganda Vita, Aureus Libellus,” in which he recom-
mended the members, as essential to their welfare, to learn
with care which constellations were favourable and which
the reverse, and to be on their guard every seventh year,
when Saturn, a very malignant planet, predominated.
IV.
The doctrine of the astrologers was, to put it into a
small compass, as follows:—
The seven principal planets and the twelve constellations
more especially influence human destiny and the events oi
the world. The seven planets were: the Sun, the Moon,
Venus, Jupiter, Mars, Mercury, and Saturn. The Sun pre-
sides over the head, the Moon the right arm and Venus the
left, Jupiter the stomach, Mars the genital organs, Mercury
the right foot, and Saturn the left.
In the constellations, Aries governs the head, Taurus
the neck, Gemini the arms and shoulders, Cancer the chest364
ASTRONOMY.
and heart, Leo the stomach, Virgo the abdomen, Libra the
loins, &c., Scorpio the genital organs, Sagittarius the thighs,
Capricorn the knees, Aquarius the legs, Pisces the feet.
Not only individuals, but even states, towns, and villages,
were placed beneath the influence of the constellations. In
the course of the sixteenth century the German astrologers
declared Frankfort-on-the-Maine to be under the influence
of * Aries, Wurzburg of Taurus, Nuremberg of Gemini,
Magdeburg of Cancer, Ulm of Leo, Heidelberg of Virgo,
Vienna of Libra, Munich of Scorpio, Stuttgardt of Sagit-
tarius, Augsburg of Capricorn, Ingolstadt of Aquarius, and
Katisbon of Pisces.
Albert the Great assigned the following influences to the
planets:—
Saturn was supposed to preside over life, change, sciences,
and buildings;
Jupiter over honour, desires, wealth, and cleanliness of
garments;
Mars over war, prisons, marriages, and feuds;
The Sun over hope, happiness, profit, and inheritances;
Venus over friendship and love;
Mercury over illness, debt, commerce, and fear;
The Moon over wounds, dreams, and theft.
Each of these planets was represented by a particular day
in the week, a colour, a metal, &c.
The Sun presided over Sunday; the Moon, Monday;
Mars, Tuesday; Mercury, Wednesday; Jupiter, Thursday;
Venus, Friday; Saturn, Saturday.
The Sun represented yellow; the Moon, white; Venus,
green; Mars, red; Jupiter, blue ; Saturn, black; and Mer-
cuiy the variegated colours.
The Sun was predominant over gold, the Moon overASTROLOGY.
365
silver, Venus over tin, Mars over iron, Jupiter over brass,
Saturn over lead, Mercury over quicksilver.
The Sun was considered beneficent and favourable;
Saturn, dreary, morose, and cold; Jupiter, temperate and
benignant; Mars, ardent; Venus, beneficent and fruitful;
Mercury, inconstant; the Moon, melanchoty.
Of the constellations, Aries, Leo, and Sagittarius are hot,
dry, and ardent; Taurus, Virgo, and Capricorn, oppressive,
cold, and dry; Gemini, Libra, and Aquarius, light, hot, and
damp; Cancer, Scorpio, and Pisces, damp, enervating and
cold.
V.
The horoscope is drawn by studying the combinations of
these influences, and examining with care how the planets
meet the constellations. For instance, if Mars meets Aries
at the moment of birth, the prognostic is courage, pride, and
long life.
Mars, according to the astrologers, augments the influence
of the constellations with which it coincides, adding valour
and strength.
Saturn, the symbol of evil influences, counteracts the
good ones.
Venus augments the good and diminishes the evil ones.
Mercury augments or diminishes the original influences,
according as he encounters a lucky or unlucky sign of the
zodiac.
The astrologers also drew prognostics from the aurorae
boreales, the comets, &c.
For the horoscope to be trustworthy, it was deemed
necessary to commence operations at the very moment of
a child’s birth, or at the very beginning of any matter of
which it was sought to know the sequel.8'66
ASTRONOMY,
The celebrated Thurneisen, a man of really great genius,
resided during the eighteenth century at the Electoral Court
of Berlin, where he was at once physician, chemist, drawer
of horoscopes, compiler of almanacs, printer, and librarian.
Pig. G2.—Birth and horoscope of a child, after a Greek bas-relief.
His reputation as an astrologer was so extensive, that
scarcely a child was born in any wealthy family of Germany,
Poland, Hungary, Denmark, or even in England, without
the .precise moment of its birth being communicated to him.
Sometimes as many as ten or twelve messages of this kind
reached him at the same time, and lie was at last so over-
charged with work, that he was compelled to hire assistants.
Whole volumes of such applications, inclusive of letters'
from Queen Elizabeth, of Prussia, are still to be seen in the
Library of Berlin. Thurneisen also compiled an annualASTROLOGY.
367
almanac of astronomy, in which lie indicated in a few sen-
tences, or with certain signs, not only the general character
of the year, but also the principal occurrences and the tem-
perature for each day.
He only gave these explanations, it is true, the year after;
still it is certain that, either out of complaisance or for some
other motive, he several times communicated his observa-
tions beforehand.
His almanac had an enormous success for twenty years,
and enabled him, together with other sources of revenue,
to amass a fortune of nearly half a million florins.
VI.
How could an art, while acknowledging that life had its
impassable limits, offer a secret for prolonging it ?
The secret was as follows:—Just as every man is subject
to the influence of a certain constellation, all the other
bodies of the animal or vegetable kingdom, and even entire
countries and houses, had their separate constellations to
which they were subject.
There was, more especially, a complete relation between
the planets and the metals.
Thus, when a man knew from what constellation his mis-
fortune or malady arose, he had only to use the food and
drink and inhabit a region placed under the influence of
the opposite planets. Thus was originated a new system
of dietetics, very different, no doubt, from that of the Greeks.
If a particular day, owing to the constellation in which it
happened to be, foreboded some kind of accident or illness,
the person threatened repaired to a place which was under368
ASTRONOMY.
a favourable constellation, or else took food and medicine
which had grown under such favourable constellation.
It was in the same way that people hoped to preserve
their lives by the wearing of amulets and talismans.
The metals and the planets being intimately related, it
was thought that by carrying a talisman composed of metals
run together, moulded, and engraved under and in harmony
with certain constellations, the wearer would be penetrated
with all the power and protection of this planet.
Thus there were talismans against the maladies due to
the influence, not of one planet only, but of all; and there
were others which, by the alloy of certain metals—a peculiar
process of fusion—were reputed to destroy the influence of
the malignant constellation which had presided over a man’s
birth, to make him prosperous in business, marriage, &c.
If the talisman had upon it the impress of Mars in the
sign of Scorpio, and if they had been fused under this con-
stellation, they rendered the wearer invulnerable and certain
of success in battle.
The French historians observe that judicial astrology was
so much in vogue during the time of Catherine de Medicis,
that no important undertaking was begun without first con-
sulting the stars; and during the reigns of Henri III. and
Henri IV. in particular, the astrologers were looked upon
as interpreters of the Divine Will.
I will terminate this chapter with a passage from Horace
which shows that the Roman poet was fully alive to the
ridiculous pretensions of the astrologers; for in Book III.,
Ode 29, he says: “ The wisdom of the Supreme has covered
the future with a veil, and he who would pierce the cloud
exposes himself to the derision of Jupiter.”
Again, in his ode to Leuconoe: “ Believe me, it is betterASTROLOGY.
369
for us not to inquire which will die first. Let us have no-
thing to clo with sorcery, and, whatever happens, let us
await with submission the decrees of Jupiter. Whether lie
intends to let us live yet some more winters, or whether
we have seen for the last time the Tuscan sea dashing
against the rocky shore, let us be wise, and filter the wine.
Let us regulate our hope according to the shortness of life,
and be resigned. Take to-day, which will perhaps have no
morrow. The moment during which I am now speaking is
already far behind us.”*
* Odes of Horace, Book i. Ode il.
\
B BCHAPTER XVIII.
the harmony of astronomy with the spirit
OF RELIGION IN ANTIQUITY.
I.
My work would be incomplete unless I attempted to show
the connection—the scientific connection, I may almost say
—which in ancient times existed between astronomy and
religious knowledge.
The chief occupation of the Chaldaean priests was the
study of astronomy. In India, the guardians of the sanc-
tuary were also the guardians of astronomy; in China, the
functions of astronomer were incorporated with those of
chief director of religious ceremonies ; in Egypt, the astro-
nomers were also priests, and used the flat roofs of the
temples as observatories.
In fine, throughout the whole of antiquity, astronomy was
always looked upon as the religious science par excellence
(see Chapter I.).
The bond which thus united religion and astronomical
science is a forced consequence of man’s nature, and of the
necessary ideas which form, so to speak, part of his exist-
ence. This is easy of demonstration.
When man attains the age of reason, and can compre-
hend what is taking place around him, he finds himself in
possession of a certain number of ideas common to every-
body else—ideas which arise spontaneously in the minds
of all men from the very fact of their being alive. I referTHE HARMONY OF ASTRONOMY.
371
to the ideas of time, cause, space, &c. (which is why they
are called necessary ideas), and to the elementary principles
arising in connection with them, which are called axioms.
Herein the idea of cause plays the principal part. When
an infant begins to speak, it does not ask if such and such
a thing has a cause, but what the cause is. “ Who made
that pretty thing? What is that pretty thing for?” The
child, of course, does not use the word cause, but from
instinct it expresses its desire to know ivhy such and such
a thing is. The older he grows, the more marked does this
idea become; and if, when he is capable of reasoning, he
was told that a certain fact had no cause, he would think
that the person who told him so was in joke, or that he was
making light of his intelligence.
This idea of cause is inseparable from the very essence
of man. It is natural to us all; it is innate in the intelli-
gence of every man from the very fact of his existence.
II.
This idea of cause has also an essential character which
must be pointed out.
Instinctively, naturally, the human mind forms an idea
of the cause analogous and proportionate to the effect by
which it is revealed, and it inspires him with different sen-
timents, according to the effects which he attributes to it.
A powerful but indiscriminate cause may excite surprise,
awe, or terror; but it does not command either admiration
or affection.
A great power, working with intelligent order, imposes a
feeling of admiration.
A great power, combining in its elements intelligence,
b b 2372
ASTRONOMY.
wisdom, and goodness, inspires at once wonder, veneration,
and affection.
Thus, an effect which manifests at once power, intelli-
gence, wisdom, and goodness, creates the idea of a cause
both powerful, intelligent, wise, and good, and inspires for
this cause a feeling of respect, veneration, and affection.
The conduct of all men not influenced by contrary passions
is a proof of it.
Moreover, each individual has but to question his own
self to be persuaded that this is the law of his soul; and
though he may break this law in his course of conduct, it
none the less exists.
The proof is also to be found in the general terms of
language which men employ.
A man is called powerful because he has done a certain
act; clever, because he has succeeded in some skilful under-
taking ; yet, before according him our attachment, we require
to know whether he is of a good or an evil disposition; for
if the latter, he might do us much harm. Another man
has become the benefactor of his country by the use of his
great abilities, his wisdom, and his goodness, which attains
the proportions of self-devotion; such a man inspires, not
only respect, but veneration and affection. And so we in-
stinctively assign to each a rank proportionate to his merits.
This is the history of the whole human race, whenever
conscience is under no restraint.
III.
Again, the aspect of the universe at large, of the mighty
ocean, of the pure, calm azure of the firmament; the motions
of the atmosphere, whether in the blast of the dark forestsTHE HARMONY OF ASTRONOMY.
373
or in the perfumed murmur of the gentle breeze ; the rising
and setting of the planets, with their inseparable and mag-
nificent cortege, their unchanging and harmonious motions
in the deep vault of heaven; all these magnificent pheno-
mena, revealed to us by the contemplation of the universe,
and belonging more or less to the domain of astronomy,
exceed in their grandeur anything that the human mind
can conceive. They instinctively give rise to the idea of
infinite power, wisdom, and goodness, and reveal to us a
cause infinitely powerful, intelligent, wise, and good; and
that cause is God.
It is not surprising, therefore, that the science, the study
of which is indissolubly connected with the contemplation
of the universe, which reveals God himself, has been looked
upon as an act of religion, as a manner of prayer.
In our day, the special study of astronomy is no longer
limited to a general contemplation of the universe; its
votaries are absorbed in examining the constitution of a
planet, like the natural philosopher studying the chemical
composition of some body, or they are engaged in transcen-
dent abstract calculations; which being the case, it is easy
to understand how it has lost much of its religious character.
IV.
All the ancients, as a rule, looked upon the universe as
the very expression and demonstration of God.
Cicero, uttering at once his own opinion and that of the
earlier philosophers, says :—
“ The fourth argument of Cleanthes (to prove that men
have an idea of the existence of gods) is much the strongest,
viz., the regulated motion of the sky, and the distinct fea-374
ASTRONOMY.
tures, the variety, the beauty, and the disposition of the
Sun, the Moon, and the other planets. It is only necessary
to look at them to see that they are not the results of chance.
Just as, when we visit a vast and well-ordered establishment,
the presence of perfect discipline and reasoned economy
reveal the presence of a very capable manager, so much the
more must the prodigious number of stars revolving from
the most remote epoch with unfailing regularity in their
courses, convince us that they are governed by a master-
mind.”*
Aristotle well remarks that, “ If we suppose men that had
always lived underground in sumptuously decorated dwell-
ings, heard of the existence of gods, and were suddenly
projected upon the Earth by an upheaving of the lower
regions which they inhabited, and there brought face to face
with the marvels of nature, is it possible to doubt but that
they would at once attribute them to the gods of whom they
had heard ? ”
Man soon comes to disregard the most marvellous objects
when his mind is pre-occupied and his attention concen-
trated upon matters of special and more immediate interest
to himself.
To quote Cicero a second time: “If we emerged from
everlasting darkness, and saw light for the first time, how
beautiful the heavens would appear to us! But because
we are accustomed to it, it ceases to impress us, and we
travel far afield in search of principles which are before
our very eyes. ... Is it reasonable in man to attribute, not
to a preconceived cause, but to chance, the fixed ’motions of
the sky, the regular course of the stars, all so connected
* Cicero’s De Nalurd, Book ii., n. 15, 95, 96, 97.THE HARMONY OF ASTRONOMY.
375
together, so well proportioned, and conducted upon such
symmetrical bases, that our reason is unable to fathom
them? When we see machines, such as a sphere or a
clock, regulated by artificial motion, we know that they are
creations of the human intelligence. Why, then, should
we doubt that the world is governed by an intelligence not
merely human, but divine ?”
The French peasants re-echo, in a rough untutored form,
the words of Cicero; for during the Reign of Terror, on
a member of the Convention telling a Vendean peasant that
the church-steeples should be demolished to sweep away the
last traces of their religious belief, the latter replied, “Well,
you may do that; but you can’t abolish our stars, and we
see them from a much greater distance.” *
V.
I now come to a very singular argument used by those
astronomers who deny the existence of a Supreme God. I
say strange, for the argument tells against those who use it.
They say: “If science has succeeded in showing that the
whole universe is regulated by fixed laws, that each star has
its own unchanging course, and that the unbroken harmony
and order which reign in immensity, opened in all its
recesses to the astronomer who is armed with powerful
instruments, are but the rigorous outcome of these laws, a
Creator is no longer necessary, and the worlds are entirely
independent of him.”
Such a process of reasoning is equivalent to saying, “ This
chronometer, which never varies, and each motion of which
* M. X. Marmier’s Discourse in tlie French Academy.376
ASTRONOMY.
is like an echo of the motion of the stars which indicate the
time, does not require the maker to come and regulate its
motions from day to day: therefore it goes of itself. But
this watch, always out of order, is incessantly under
repair, so we see that it did not create itself. This is what
such a pitiful train of reasoning leads up to, and I must
almost ask the readers pardon for exposing it in all its
nakedness.
It is more than a century since Lalande had the hardi-
hood to exclaim, “ I have examined the whole expanse of
the heavens, and I can find no trace of God.” And this
because he had observed in every direction the traces of
infinite wisdom!
If the universe had been so imperfect that the Almighty was
incessantly occupied in replacing the stars in their courses,
His existence would not be called into question; but because
His work bears the impress of infinite wisdom, we adduce
that very fact as a reason for contesting the existence of
the Maker! Is it possible to find a more striking instance
of unreason ?
Should we not rather feel that the further the study of
the universe is carried, the more convincing are the proofs
of the grandeur and the perfection, not only of it, but of
Him who created it ?
VI.
Man naturally and instinctively attributes a cause to each
effect, and this imperious moral instinct has never been
found wrong, when it lias been possible to trace back from
the effect to the cause. It is the same imperious instinct,
the same law of the soul, which makes him attribute anTHE HARMONY OF ASTRONOMY.
377
infinite cause to the universe. Therefore, if we stop half
way, we are wanting in logic; we break the chain, of
reasoning, just as if we refused to recognise a cause to a
series of phenomena.
This is so true, that to tell a man who possesses all his
reasoning faculties, and who is unbiassed by any external
influences, that the wTorld was created of itself, that there
is no sovereign cause—in a word, no god—is to revolt his
common sense. It is equivalent to asking him to believe that
there is such a thing as an effect without a cause. It is
even worse, for not only do his mental faculties resent such
a suggestion, but he will feel horrified at such a patent con-
tradiction of moral certainties.
Thus, to deny the sovereign cause—to deny God—is to
run counter to logic, to the laws of intelligence, and of
feeling. I will go even further, and assert that it is con-
trary to the principles of science, for to admit the possibility
of effect without cause is to abandon anything in the shape
of scientific method, and I repeat that the law of causation
ascends by successive links up to the supreme cause. To
stop half-way is to break that chain of reasoning which is
the consequence of the laws of the soul.
Those who run counter to the rules of logic and science
in this way argue: But how do you explain the Supreme
Cause ?
This is a different question; but whether or not we can
explain the Supreme Cause, the law of our soul none the
less exists, and no reasoning should induce us to violate it.
This also holds true of the objections which may be
derived from special facts against the infinite wisdom,
justice, and goodness of which the general laws of the
universe bear the imprint. For these objections to possess378
ASTRONOMY.
any force, those who urge them would first need to have at
their fingers’ ends the past, present, and future history of
the worlds, about which we know so little that no argument
can be based upon it.
VII.
Nevertheless, the thought that men of high intellect have
come to doubt the existence of a Supreme Cause, creates
a very uneasy feeling in many minds. Those who are thus
painfully affected in their habitual beliefs sa}": These savants
must have discovered some very terrible secrets -which they
do not dare to reveal, and which prove to them that God
is a myth. Otherwise, how is it that, with an intellect
greater and more fully developed than mine, they do not
feel as I do, and adore with even greater fervency the Maker
of all the marvels which they have laid bare ? This is a
natural course of reasoning; but, on reflection, the facts
which seem so strange to them admit of a simple explana-
tion. Those who deny God have not discovered any terrible
secrets; for everything in science, more especially in the
advanced sciences, tends to augment the knowledge of causes
and laws, and consequently tends to reveal to us a Supreme
Cause, and make us appreciate still more highly His great-
ness and wisdom.
How can they who thus stop short in their train of rea-
soning assert that the universe proves nothing—that the
Supreme Cause does not exist ? It is clear that they cannot
make such a statement without being false to themselves
and to those whom they address, for they have no evidence
to offer in its support.
And if they say so in the name of science, they take thatTHE HARMONY OF ASTRONOMY.
379
name in vain; for science has never shown that there can
be an effect without a cause. On the contrary, the farther
it progresses, the more striking is its demonstration of the
dependency of effect upon cause, the nearer does it approach
to the laws which regulate their connexion, and so towards
a knowledge of the Supreme Cause.
All that man can do in good faith in this matter is to doubt.
He may reach this sad condition either by allowing his
intellectual faculties to take a false direction, which deprives
them of their spontaneity, and so of their liberty (which
comes of dwelling too much on exclusive studies) or by the
habitual current of his ideas. With some natures, passion
also will so trouble and prejudice the mind, that it cannot
perceive matters within the range of an ordinary intellect.
Thus a man may, with the best intentions, become the
victim of involuntaiy illusions; without losing his reason,
he may lose the notions of common sense in many matters,
and his faculties will become warped in a way incredible to
those who have not studied the chapter which is at once
physiological and psychological. The mind constantly fixed
upon one thing, losing its spontaneity, will account for it.
Or perhaps the following paragraph will set the matter in
a clearer light.
It is our common sense and reasoning power that reveal
to us the Supreme Cause and the great truths of the
moral world. But the widest development of the intellect
and all the erudition in the world add nothing to the evidence
of common sense and the rectitude of judgment; on the con-
trary, there is a danger, as the intellect develops, of common
sense becoming contracted and unable to seize the notions
which belong to its domain, and upon which all human
knowledge is based.380
ASTRONOMY.
This may be remarked every clay and every hour in
matters far less important than the great truths of which
I am speaking. We encounter every day rough uneducated
people with an amount of common sense and a rectitude of
judgment greater than is possessed by many persons of far
higher intellectual attainments. It must be evident to all
those who study the question, that the great truths upon
which are based the first principles of morality come within
the domain of common sense; not within that of science
strictly speaking, which, far from helping to demonstrate
them, often serves to make their study more difficult.
VIII.
There is another observation of some importance which
I must not omit.
Man possesses not only the faculty of knowledge, but he
is endowed with sentiment, that is to say, the faculty of
being moved by anything grand or beautiful, of feeling the
expression of it in his inner soul, and of forming a dis-
interested attachment to it.
But all men do not possess these two faculties in the
same degree; and it is, indeed, important to bear in mind
that some men have great intellect, and even a large fund
of sensibility and susceptibility, without possessing a shadow
of sentiment. They are unable to appreciate or take in
anything which does not appeal to their intellect; the
splendours of the universe make no impression upon them,
and if it unfortunately happens that their common sense be-
comes obscured by the concentration of their intellect upon
a single object, or by the influence of some particular pas-
sion, their apprehension of moral facts seems to be entirelyTHE HARMONY OP ASTRONOMY.
381
deadened. They are devoid of the sentiment of feeling which
will often serve to replace a deficiency of common sense.
Intellect shows us what exists and what it is our duty to
do; with sentiment we feel all this without being able to
give the reason why. We may say with Pascal: “ For the
heart has its reasons, of which judgment so-called knows
nothingor with Vauvenargues, in his “ Keflexions et
Maximes ” : “ Judgment and sentiment, each in their turn
replacing one another, give good counsel.” Those who are
endowed with intellect alone possess but the half of a
human soul.
To those endowed with a great amount of sentiment, the
aspect of the universe reveals the Supreme Cause, not only
to their intelligence as a logical consequence, but it also
causes them to feel, in spite of themselves it may some-
times be, the existence and the presence of the invisible
Cause.
This is why those more refined and elevated natures in
which the heart and the intellect are alike far above the
level have never questioned for an instant the existence
of a God; they may have been unable to admit the truth
of some particular religion or dogma, but they have never
felt any doubt as to the existence of the Supreme Cause,
infinitely powerful, wise, and good. Moreover, all truly
great men—all those whose names are illustrious in the
world’s annals as the benefactors of humanity—have been
believers in God.
It seems to me, therefore, that all these considerations
tend to demonstrate that the bond which in ancient times
united astronomical science and religion has its origin in
the very nature of man and his necessary relations with the
universe; that the idea of causation leads up to the recog-382
ASTRONOMY.
nition of the Supreme Being as a rigorous and inevitable
outcome of the laws of the mind; and that the universe,
being His natural expression, renders Him present to our
sentiment.
Fig. 63.—Atlas (from the Farnese Collection).
REFERENCE TO NAMES QUOTED IN
THIS WORK.
Abraham, 10.
Achorams, 17.
Adams, 257.
Airy, 149.
Albert the Great, 364.
Alexander (Emp.), 9.
Anaxagoras, 15.
Anaximander, 15.
Arago, 52, 66, 85, 86, 162, 209, 217,
238, 255, 299, 302, 355.
Aristarchus (of Samos), 16, 163.
Aristotle, 9, 16, 374.
Babiuet, vi., 142, 229, 236, 293,
299, 301.
Bailie, 149,186.
Bailly, 2, 9.
Baily, 214.
Baumhauer, 320.
Becquerel, 76, 79.
Benthey, 3.
Bernardin de Saint-Pierre, 127.
Bertrand, 144, 148, 352.
Bessel, 299.
Bianchini, 121.
Biela, 311.
Biot, 50, 331.
Boriaparte, 120.
Bond, 254. .
Borelly, 314.
Bouguer, 169.
Bouillaud, 195.
Bouvard, 255.
Brorsen, 313.
Buch (de), 169.
Byrg, 154.
Callippus, 7.
Calisthenes, 9.
Capello, 78.
Carlini, 149.
Caselli, 244.
Cassini, 2, 100, 127, 148, 253, 305.
Castelli, 120.
Cavendish, 149.
Chladni, 329, 332.
Champollion, 14.
Chapelas, 341.
Cliappe, 126.
Cheux, 78, 88.
Chun, 5.
Cicero, 373.
Clairault, 147, 197, 299, 307.
Clausen, 311.
Clery, 209.
Colomhus (Christopher), 221.
Copernicus, 20, 66, 115.
Cornu, 43, 149.
Coulvier-Gravier, 341.
Cr6ty (de), 187.
Croll, 178,181.
D’Alembert, 197.
Damoiseau, 309.
D’Arrest, 312.
Daubree, 322, 324, 328, 329.
Debray, 96.
Delambre, 298.
Delaunay, 39, 53, 57, 89, 90, 138,
194,219,256,269,292,305,315,333.
Denza, 338.
Descartes, 27, 41.
Didot (Amb. Firmin), 22.
Diodorus Siculus, 221.
Ditte, 56.
Dubois de Jancigny, 5.
Dumas, 56, 90.
Elie-de-Beaumont, 11, 94, 130, 165,
318.
Encke, 309, 311.
Enaeas, 119.
Eudoxes, 17.m
PRINCIPAL NAMES CITED.
.Euler, 197.
Eversman, 321.
Fabricius, 74.
Faye, 64, 72, 78, 88, 89, 90, 126,
149, 291, 313, 337.
Eizeau, 42, 95.
Elammarion, 243.
Fontana, 244.
Eontenelle, 21, 116, 222.
Foucault, 43. ‘
Fourier, 134.
Franck, 357.
Frankland, 96.
Franklin, 179.
Frisch, 153.
Fraunhofer, 54.
Galileo, 120, 188.
Galle, 257.
Gambard, 311.
Gaubil, 8.
Goldschmidt, 313,
Grad, 166, 169, 180.
Gratry, v.
Gregory XIII., 347.
Grow, 241.
Guillemin, 253.
Guynemer, 189.
Halley, 125, 192, 216, 218,279, 306.
Hansen, 255.
Hautefeuille, 56.
Herodotus, 220, 358.
Herschel, 36, 38, 85, 238, 250, 254,
262, 299, 312.
Hesiod, 274, 356/
Hi, 7.
Hind, 314.
Hipparchus, 16, 274, 424.
Hirne, 251, 254.
Ho, 7.
Homer, 118, 237, 274, 317.
Horace, 368.
Hugi, 169.
Huggins, 57, 63, 291.
Humboldt, 169, 348.
Hutton, 149.
Huyghens, 254.
Inriclis, 38.
James, 149.
Janssen, 59, 90, 202, 210, 211, 212,
213.
Job, 10, 274.
Jordan Bruno, 73.
Josephus, 2.
Joy son, 241.
Julius Cajsar, 17, 346.
Juvenal, 359.
Kant, 38.
Keller, 143.
Kepler, 16, 34,39,151, 195, 357.
KirchofF, 55, 85.
La Condamine, 147.
La Hire, 121, 219.
Lalande, 74, 305, 308, 376.
Lame, 143.
Lamy, 56.
Laplace, 2, 38, 85, 194, 308, 331.
Lassell, 254.
Latronne, 13.
Lavoisier, 10S. ,
Lecoq (de Boisbaudran), 56.
Legentil, 125.
Leibnitz, 30.
Le Terrier, 35, 44, 92,255,257, 313,
334, 335, 337.
Lexell, 297.
Liais, 101, 302,
Lockyer, 213.
Lcewy, 314.
Lucanus, 229.
Lucretius, 98.
McClear, 314.
Maedler, 242.
Magellan, 136.
Mairan (de), 100.
Marie-Davy, 183, 186.
Marmier (X.), 162, 375.
Marsilius Ficinus, 363.
Maskelyne, 149.
Maupertuis, 147.
Mechain, 314.
Meeeh, 179.
Meignan (Mgr.), 344.
Melloni, 186.
Messier, 297.
Meton, 9, 219.
Meunier (S.), 243,332. .
Miller, 57.
Milton, 318.
Mitchell, 149.
Moesklin, 154.
Montezuma, 362.PRINCIPAL NAMES CITED,
385
Moller, 313.
Newton, 29, 41, 45, 142, 195, 297,
335.
Oppolzer, 334.
Ossian, 194, 318.
Ovid, 265, 275,
Parasara, 3.
Pascal, 381.
Pauthier, 6, 8.
Pensa, 363.
Perrey, 131.
Pctfirs 334
Petit, 85,125,155,188,262,266,304.
Phillips, 241.
Philolaus, 20, 163.
Piazzi Smith, 186.
Picard, 142, 145, 195.
Pictet, 321.
Plana, 11, 132,149.
Playfair, 2,149.
Pliny, 17, 328.
Plutarch, 203, 224, 226, 327, 346,
.	359.
Poisson, 132, 310.
Pompey, 18.
Pons, 310.
Pont6coulant (de), 309.
Porro, 211.
Poseidonius, 17.
Pouillet, 93, 179.
Prados (de), 303,
Ptolemy, 9,17, 19,197.
Ptolemies (the), 14.
Pythagoras, 15, 290.
Pytlieas, 16, 229.	j
Quinet, 211.	!
Quetelet, 321.
Radau, 109.
Rankine, 95.
Raymond (X.), 5.
Reich, 149.
Renou, 169.
Respighi, 104.
Rey (de Morande), 168.
Richet, 145.
Roemer, 42, 219, 249.
Rosse (Lord), 186.
BRADBURV, AQNEWj & GO
Royet, 92.
Sainte-Claire Deville (Oh.), 76, 320.
Sainte-Claire Deville (H.), 96.
Sannat-Solarot, 78.
Scheiner, 74.
Schiaparelli, 333, 334.
Schmidt, 294, 326.
Schrcoter, 113, 121.
Schwahe, 75.	.	*
Secchi, 34, 37, 47, 61, 71, 75, 80, 87,
88, 89, 93, 97,110, 210, 213, 241,
269, 270, 272, 312, 326, 335.
Sedillot, 344.
Seneca, 293, 296.
Seth, 2.
Silbermann (J. J.), 103, 327, 369.
Smyth, 299.
Sophocles, 203.
Sosigenes, 17.
Spserer, 93.
Stephan, 311.
Struve, 267, 299.
Tacchini, 77,247.
Tacitus, 225, 360,362.
Tarry, 321.
Tarutius, 359.
Tchoung-King, 7.
Thales, 15, 220.
Theon (of Smyrna), 66.
Thomson, 94, 199, 291.
Thrasyllus, 361.
Thurneisen, 366.
Tisserand, 314.
Toost, 56.
Tuttle, 294.
Tycho-Brah6, 24.
Varro, 120, 359.
Vaullet, 169.
Vauvenargus, 381.
Verne, 352.
Vicaire, 87, 93.
Vihot, 243.
Volpicelli, 186,253.
Wilson, 69.
Winnecke, 293/ 315.
Wollaston, 54, 301.
Yao, 5.
Young, 53, 84.
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