CHAPTER I

A SHORT HISTORICAL SKETCH OF ASTRONOMY


Astronomy is the oldest and most sublime of all the sciences. To a
contemplative observer of the heavens, the number and brilliancy of the
stars, the lustre of the planets, the silvery aspect of the Moon, with
her ever-changing phases, together with the order, the harmony, and
unison pervading them all, create in his mind thoughts of wonder and
admiration. Occupying the abyss of space indistinguishable from
infinity, the starry heavens in grandeur and magnificence surpass the
loftiest conceptions of the human mind; for, at a distance beyond the
range of ordinary vision, the telescope reveals clusters, systems,
galaxies, universes of stars--suns--the innumerable host of heaven, each
shining with a splendour comparable with that of our Sun, and, in all
likelihood, fulfilling in a similar manner the same beneficent purposes.

The time when man began to study the stars is lost in the antiquity of
prehistoric ages. The ancient inhabitants of the Earth regarded the
heavenly bodies with veneration and awe, erected temples in their
honour, and worshipped them as deities. Historical records of astronomy
carry us back several thousand years. During the greater part of this
time, and until a comparatively recent period, astronomy was associated
with astrology--a science which originated from a desire on the part of
mankind to penetrate the future, and which was based upon the supposed
influence of the heavenly bodies upon human and terrestrial affairs. It
was natural to imagine that the overruling power which governed and
directed the course of sublunary events resided in the heavens, and that
its decrees might be understood by watching the movements of the
heavenly bodies under its control. It was, therefore, believed that by
observing the configuration of the planets and the positions of the
constellations at the instant of the birth of an individual, his
horoscope, or destiny, could be foretold; and that by making
observations of a somewhat similar nature the occurrence of events of
public importance could be predicted. When, however, the laws which
govern the motions of the heavenly bodies became better known, and
especially after the discovery of the great law of gravitation,
astrology ceased to be a belief, though for long after it retained its
power over the imagination, and was often alluded to in the writings of
poets and other authors.

In the early dawn of astronomical science, the theories upheld with
regard to the structure of the heavens were of a simple and primitive
nature, and might even be described as grotesque. This need occasion no
surprise when we consider the difficulties with which ancient
astronomers had to contend in their endeavours to reduce to order and
harmony the complicated motions of the orbs which they beheld circling
around them.

The grouping of the stars into constellations having fanciful names,
derived from fable or ancient mythology, occurred at a very early
period, and though devoid of any methodical arrangement, is yet
sufficiently well-defined to serve the purposes of modern astronomers.
Several of the ancient nations of the earth, including the Chaldeans,
Egyptians, Hindus, and Chinese, claim to have been the earliest
astronomers. Chinese records of astronomy reveal an antiquity of near
3,000 years B.C., but they contain no evidence that their authors
possessed any scientific knowledge, and they merely record the
occurrence of solar eclipses and the appearances of comets.

It is not known when astronomy was first studied by the Egyptians; but
what astronomical information they have handed down is not of a very
intelligible kind, nor have they left behind any data that can be relied
upon. The Great Pyramid, judging from the exactness with which it faces
the cardinal points, must have been designed by persons who possessed a
good knowledge of astronomy, and it was probably made use of for
observational purposes.

It is now generally admitted that correct astronomical observations were
first made on the plains of Chaldea, records of eclipses having been
discovered in Chaldean cities which date back 2,234 years B.C. The
Chaldeans were true astronomers: they made correct observations of the
risings and settings of the heavenly bodies; and the exact orientation
of their temples and public buildings indicates the precision with which
they observed the positions of celestial objects. They invented the
zodiac and gnomon, made use of several kinds of dials, notified
eclipses, and divided the day into twenty-four hours.

To the Greeks belongs the credit of having first studied astronomy in a
regular and systematic manner. THALES (640 B.C.) was one of the earliest
of Greek astronomers, and may be regarded as the founder of the science
among that people. He was born at Miletus, and afterwards repaired to
Egypt for the purpose of study. On his return to Greece he founded the
Ionian school, and taught the sphericity of the Earth, the obliquity of
the ecliptic, and the true causes of eclipses of the Sun and Moon. He
also directed the attention of mariners to the superiority of the Lesser
Bear, as a guide for the navigation of vessels, as compared with the
Great Bear, by which constellation they usually steered. Thales believed
the Earth to be the centre of the universe, and that the stars were
composed of fire; he also predicted the occurrence of a great solar
eclipse.

Thales had for his successors Anaximander, Anaximenes, and Anaxagoras,
who taught the doctrines of the Ionian school.

The next great astronomer that we read of is PYTHAGORAS, who was born at
Samos 590 B.C. He studied under Thales, and afterwards visited Egypt and
India, in order that he might make himself familiar with the scientific
theories adopted by those nations. On his return to Europe he founded
his school in Italy, and taught in a more extended form the doctrines of
the Ionian school. In his speculations with regard to the structure of
the universe he propounded the theory (though the reasons by which he
sustained it were fanciful) that the Sun is the centre of the planetary
system, and that the Earth revolves round him. This theory--the accuracy
of which has since been confirmed--received but little attention from
his successors, and it sank into oblivion until the time of Copernicus,
by whom it was revived. Pythagoras discovered that the Morning and
Evening Stars are one and the same planet.

Among the famous astronomers who lived about this period we find
recorded the names of Meton, who introduced the Metonic cycle into
Greece and erected the first sundial at Athens; Eudoxus, who persuaded
the Greeks to adopt the year of 365-1/4 days; and Nicetas, who taught
that the Earth completed a daily revolution on her axis.

The Alexandrian school, which flourished for three centuries prior to
the Christian era, produced men of eminence whose discoveries and
investigations, when arranged and classified, enabled astronomy to be
regarded as a true theoretical science. The positions of the fixed stars
and the paths of the planets were determined with greater accuracy, and
irregularities of the motions of the Sun and Moon were investigated with
greater precision. Attempts were made to ascertain the distance of the
Sun from the Earth, and also the dimensions of the terrestrial sphere.
The obliquity of the ecliptic was accurately determined, and an arc of
the meridian was measured between Syene and Alexandria. The names of
Aristarchus, Eratosthenes, Aristyllus, Timocharis, and Autolycus, are
familiarly known in association with the advancement of the astronomy of
this period.

We now reach the name of HIPPARCHUS of Bithynia (140 B.C.), the most
illustrious astronomer of antiquity, who did much to raise astronomy to
the position of a true science, and who has also left behind him ample
evidence of his genius 'as a mathematician, an observer, and a
theorist.' We are indebted to him for the earliest star catalogue, in
which he included 1,081 stars. He discovered the Precession of the
Equinoxes, and determined the motions of the Sun and Moon, and also the
length of the year, with greater precision than any of his predecessors.
He invented the sciences of plane and spherical trigonometry, and was
the first to use right ascensions and declinations.

The next astronomer of eminence after Hipparchus was PTOLEMY (130 A.D.),
who resided at Alexandria. He was skilled as a mathematician and
geographer, and also excelled as a musician. His chief discovery was an
irregularity of the lunar motion, called the '_evection_.' He was also
the first to observe the effect of the refraction of light in causing
the apparent displacement of a heavenly body from its true position.
Ptolemy devoted much of his time to extending and improving the theories
of Hipparchus, and compiled a great treatise, called the 'Almagest,'
which contains nearly all the knowledge we possess of ancient astronomy.
Ptolemy's name is, however, most widely known in association with what
is called the Ptolemaic theory. This system, which originated long
before his time, but of which he was one of the ablest expounders, was
an attempt to establish on a scientific basis the conclusions and
results arrived at by early astronomers who studied and observed the
motions of the heavenly bodies. Ptolemy regarded the Earth as the
immovable centre of the universe, round which the Sun, Moon, planets,
and the entire heavens completed a daily revolution in twenty-four
hours. After the death of Ptolemy no worthy successor was found to
occupy his place, the study of astronomy began to decline among the
Greeks, and after a time it ceased to be cultivated by that people.

The Arabs next took up the study of astronomy, which they prosecuted
most assiduously for a period of four centuries. Their labours were,
however, confined chiefly to observational work, in which they
excelled; unlike their predecessors, they paid but little attention to
speculative theories--indeed, they regarded with such veneration the
opinions held by the Greeks, that they did not feel disposed to question
the accuracy of their doctrines. The most eminent astronomer among the
Arabs was ALBATEGNIUS (680 A.D.). He corrected the Greek observations,
and made several discoveries which testified to his abilities as an
observer. IBN YUNIS and ABUL WEFU were Arab astronomers who earned a
high reputation on account of the number and accuracy of their
observations. In Persia, a descendant of the famous Genghis Khan erected
an observatory, where astronomical observations were systematically
made. Omar, a Persian astronomer, suggested a reformation of the
calendar which, if it had been adopted, would have insured greater
accuracy than can be attained by the Gregorian style now in use. In
1433, Ulugh Beg, who resided at Samarcand, made many observations, and
constructed a star catalogue of greater exactness than was known to
exist prior to his time. The Arabs may be regarded as having been the
custodians of astronomy until the time of its revival in another quarter
of the Globe.

After the lapse of many centuries, astronomy was introduced into Western
Europe in 1220, and from that date to the present time its career has
been one of triumphant progress. In 1230, a translation of Ptolemy's
'Almagest' from Arabic into Latin was accomplished by order of the
German Emperor, Frederick II.; and in 1252 Alphonso X., King of Castile,
himself a zealous patron of astronomy, caused a new set of astronomical
tables to be constructed at his own expense, which, in honour of his
Majesty, were called the 'Alphonsine Tables.' Purbach and Regiomontanus,
two German astronomers of distinguished reputation, and Waltherus, a man
of considerable renown, made many important observations in the
fifteenth century.

The most eminent astronomer who lived during the latter part of this
century was Copernicus. NICOLAS COPERNICUS was born February 19, 1473,
at Thorn, a small town situated on the Vistula, which formed the
boundary between the kingdoms of Prussia and Poland. His father was a
Polish subject, and his mother of German extraction. Having lost his
parents early in life, he was educated under the supervision of his
uncle Lucas, Bishop of Ermland. Copernicus attended a school at Thorn,
and afterwards entered the University of Cracow, in 1491, where he
devoted four years to the study of mathematics and science. On leaving
Cracow he attached himself to the University of Bologna as a student of
canon law, and attended a course of lectures on astronomy given by
Novarra. In the ensuing year he was appointed canon of Frauenburg, the
cathedral city of the Diocese of Ermland, situated on the shores of the
Frisches Haff. In the year 1500 he was at Rome, where he lectured on
mathematics and astronomy. He next spent a few years at the University
of Padua, where, besides applying himself to mathematics and astronomy,
he studied medicine and obtained a degree. In 1505 Copernicus returned
to his native country, and was appointed medical attendant to his uncle,
the Bishop of Ermland, with whom he resided in the stately castle of
Heilsberg, situated at a distance of forty-six miles from Frauenburg.
Copernicus lived with his uncle from 1507 till 1512, and during that
time prosecuted his astronomical studies, and undertook, besides, many
arduous duties associated with the administration of the diocese; these
he faithfully discharged until the death of the Bishop, which occurred
in 1512. After the death of his uncle he took up his residence at
Frauenburg, where he occupied his time in meditating on his new
astronomy and undertaking various duties of a public character, which he
fulfilled with credit and distinction. In 1523 he was appointed
Administrator-General of the diocese. Though a canon of Frauenburg,
Copernicus never became a priest.

After many years of profound meditation and thought, Copernicus, in a
treatise entitled 'De Revolutionibus Orbium Celestium,' propounded a new
theory, or, more correctly speaking, revived the ancient Pythagorean
system of the universe. This great work, which he dedicated to Pope Paul
III., was completed in 1530; but he could not be prevailed upon to have
it published until 1543, the year in which he died. In 1542 Copernicus
had an apoplectic seizure, followed by paralysis and a gradual decay of
his mental and vital powers. His book was printed at Nuremberg, and the
first copy arrived at Frauenburg on May 24, 1543, in time to be touched
by the hands of the dying man, who in a few hours after expired. The
house in which Copernicus lived at Allenstein is still in existence, and
in the walls of his chamber are visible the perforations which he made
for the purpose of observing the stars cross the meridian.

Copernicus was the means of creating an entire revolution in the science
of astronomy, by transferring the centre of our system from the Earth to
the Sun. He accounted for the alternation of day and night by the
rotation of the Earth on her axis, and for the vicissitudes of the
seasons by her revolution round the Sun. He devoted the greater part of
his life to meditating on this theory, and adduced several weighty
reasons in its support. Copernicus could not help perceiving the
complications and entanglements by which the Ptolemaic system of the
universe was surrounded, and which compared unfavourably with the simple
and orderly manner in which other natural phenomena presented themselves
to his observation. By perceiving that Mars when in opposition was not
much inferior in lustre to Jupiter, and when in conjunction resembled a
star of the second magnitude, he arrived at the conclusion that the
Earth could not be the centre of the planet's motion. Having discovered
in some ancient manuscripts a theory, ascribed to the Egyptians, that
Mercury and Venus revolved round the Sun, whilst they accompanied the
orb in his revolution round the Earth, Copernicus was able to perceive
that this afforded him a means of explaining the alternate appearance of
those planets on each side of the Sun. The varied aspects of the
superior planets, when observed in different parts of their orbits, also
led him to conclude that the Earth was not the central body round which
they accomplished their revolutions. As a combined result of his
observation and reasoning Copernicus propounded the theory that the Sun
is the centre of our system, and that all the planets, including the
Earth, revolve in orbits around him. This, which is called the
Copernican system, is now regarded as, and has been proved to be, the
true theory of the solar system.

TYCHO BRAHE was a celebrated Danish astronomer, who earned a deservedly
high reputation on account of the number and accuracy of his
astronomical observations and calculations. The various astronomical
tables that were in use in his time contained many inaccuracies, and it
became necessary that they should be reconstructed upon a more correct
basis. Tycho possessed the practical skill required for this kind of
work.

He was born December 14, 1546, at Knudstorp, near Helsingborg. His
father, Otto Brahe, traced his descent from a Swedish family of noble
birth. At the age of thirteen Tycho was sent to the University of
Copenhagen, where it was intended he should prepare himself for the
study of the law.

The prediction of a great solar eclipse, which was to happen on August
21, 1560, caused much public excitement in Denmark, for in those days
such phenomena were regarded as portending the occurrence of events of
national importance. Tycho looked forward with great eagerness to the
time of the eclipse. He watched its progress with intense interest, and
when he perceived all the details of the phenomenon occur exactly as
they were predicted, he resolved to pursue the study of a science by
which, as was then believed, the occurrence of future events could be
foretold. From Copenhagen Tycho Brahe was sent to Leipsic to study
jurisprudence, but astronomy absorbed all his thoughts. He spent his
pocket-money in purchasing astronomical books, and, when his tutor had
retired to sleep, he occupied his time night after night in watching the
stars and making himself familiar with their courses. He followed the
planets in their direct and retrograde movements, and with the aid of a
small globe and pair of compasses was able by means of his own
calculations to detect serious discrepancies in the Alphonsine and
Prutenic tables. In order to make himself more proficient in calculating
astronomical tables he studied arithmetic and geometry, and learned
mathematics without the aid of a master. Having remained at Leipsic for
three years, during which time he paid far more attention to the study
of astronomy than to that of law, he returned to his native country in
consequence of the death of an uncle, who bequeathed him a considerable
estate. In Denmark he continued to prosecute his astronomical studies,
and incurred the displeasure of his friends, who blamed him for
neglecting his intended profession and wasting his time on astronomy,
which they regarded as useless and unprofitable.

Not caring to remain among his relatives, Tycho Brahe returned to
Germany, and arrived at Wittenberg in 1566. Whilst residing here he had
an altercation with a Danish gentleman over some question in
mathematics. The quarrel led to a duel with swords, which terminated
rather unfortunately for Tycho, who had a portion of his nose cut off.
This loss he repaired by ingeniously contriving one of gold, silver, and
wax, which was said to bear a good resemblance to the original. From
Wittenberg Tycho proceeded to Augsburg, where he resided for two years.
Here he made the acquaintance of several men distinguished for their
learning and their love of astronomy. During his stay at Augsburg he
constructed a quadrant of fourteen cubits radius, on which were
indicated the single minutes of a degree; he made many valuable
observations with this instrument, which he used in combination with a
large sextant.

In 1571 Tycho returned to Denmark, where his fame as an astronomer had
preceded him, and was the means of procuring for him a hearty welcome
from his relatives and friends. In 1572, when returning one night from
his laboratory--for Tycho studied alchemy as well as astronomy--he
beheld what appeared to be a new and brilliant star in the
constellation Cassiopeia, which was situated overhead. He directed the
attention of his companions to this wonderful object, and all declared
that they had never observed such a star before. On the following night
he measured its distance from the nearest stars in the constellation,
and arrived at the conclusion that it was a fixed star, and beyond our
system.

This remarkable object remained visible for sixteen months, and when at
its brightest rivalled Sirius. At first it was of a brilliant white
colour, but as it diminished in size it became yellow; it next changed
to a red colour, resembling Aldebaran; afterwards it appeared like
Saturn, and as it grew smaller it decreased in brightness, until it
finally became invisible. In 1573 Tycho Brahe married a peasant-girl
from the village of Knudstorp. This imprudent act roused the resentment
of his relatives, who, being of noble birth, were indignant that he
should have contracted such an alliance. The bitterness and mutual
ill-feeling created by this affair became so intense that the King of
Denmark deemed it advisable to endeavour to bring about a
reconciliation.

After this Tycho returned to Germany, and visited several cities before
deciding where he should take up his permanent residence.

His fame as an astronomer was now so great that he was received with
distinction wherever he went, and on the occasion of a visit to
Hesse-Cassel he spent a few pleasant days with William, Landgrave of
Hesse, who was himself skilled in astronomy.

Frederick II., King of Denmark, having recognised Tycho Brahe's great
merits as an astronomer, and not wishing that his fame should add lustre
to a foreign Court, expressed a desire that he should return to his
native country, and as an inducement offered him a life interest in the
island of Huen, in the Sound, where he undertook to erect and equip an
observatory at his own expense; the King also promised to bestow upon
him a pension, and grant him other emoluments besides.

Tycho gladly accepted this generous offer, and during the construction
of the observatory occupied his time in making a magnificent collection
of instruments and appliances adapted for observational purposes. This
handsome edifice, upon which the King of Denmark expended a sum of
20,000_l._, was called 'Uranienburg' ('The Citadel of the Heavens').
Here Tycho resided for a period of twenty years, during which time he
pursued his astronomical labours with untiring energy and zeal, and made
a large number of observations and calculations of much superior
accuracy to any that existed previously, which were afterwards of great
service to his successors. During his long residence at Huen, Tycho was
visited by many distinguished persons, who were attracted to his island
home by his fame and the magnificence of his observatory. Among them was
James VI. of Scotland, who, whilst journeying to the Court of Denmark
on the occasion of his marriage to a Danish princess, paid Tycho a
visit, and enjoyed his hospitality for a week. The King was delighted
with all that he saw, and on his departure presented Tycho with a
handsome donation, and at his request composed some Latin verses, in
which he eulogised his host and praised his observatory.

The island of Huen is situated about six miles from the coast of
Zealand, and fourteen from Copenhagen. It has a circumference of six
miles, and consists chiefly of an elevated plateau, in the centre of
which Tycho erected his observatory, the site of which is now marked by
two pits and a few mounds of earth--all that remains of Uranienburg. All
went well with Tycho Brahe during the lifetime of his noble patron; but
in 1588 Frederick II. died, and was succeeded by his son, a youth eleven
years of age.

The Danish nobles had long been jealous of Tycho's fame and reputation,
and on the death of the King an opportunity was afforded them of
intriguing with the object of accomplishing his downfall. Several false
accusations were brought against him, and the Court party made the
impoverished state of the Treasury an excuse for depriving him of his
pension and emoluments granted by the late King.

Tycho was no longer able to bear the expense of maintaining his
establishment at Huen, and fearing that he might be deprived of the
island itself, he took a house in Copenhagen, to which he removed all
his smaller instruments.

During his residence in the capital he was subjected to annoyance and
persecution. An order was issued in the King's name preventing him from
carrying on his chemical experiments, and he besides suffered the
indignity of a personal assault. Tycho Brahe resolved to quit his
ungrateful country and seek a home in some foreign land, where he should
be permitted to pursue his studies unmolested and live in quietness and
peace. He accordingly removed from the island of Huen all his
instruments and appliances that were of a portable nature, and packed
them on board a vessel which he hired for the purpose of transport, and,
having embarked with his family, his servants, and some of his pupils
and assistants, 'this interesting barque, freighted with the glory of
Denmark,' set sail from Copenhagen about the end of 1597, and having
crossed the Baltic in safety, arrived at Rostock, where Tycho found some
old friends waiting to receive him. He was now in doubt as to where he
should find a home, when the Austrian Emperor Rudolph, himself a liberal
patron of science and the fine arts, having heard of Tycho Brahe's
misfortunes, sent him an invitation to take up his abode in his
dominions, and promised that he should be treated in a manner worthy of
his reputation and fame.

Tycho resolved to accept the Emperor's kind invitation, and in the
spring of 1599 arrived at Prague, where he found a handsome residence
prepared for his reception.

He was received by the Emperor in a most cordial manner and treated with
the greatest kindness. An annual pension of three thousand crowns was
settled upon him for life, and he was to have his choice of several
residences belonging to his Majesty, where he might reside and erect a
new observatory. From among these he selected the Castle of Benach, in
Bohemia, which was situated on an elevated plateau and commanded a wide
view of the horizon.

During his residence at Benach Tycho received a visit from Kepler, who
stayed with him for several months in order that he might carry out some
astronomical observations. In the following year Kepler returned, and
took up his permanent residence with Tycho, having been appointed
assistant in his observatory, a post which, at Tycho's request, was
conferred upon him by the Emperor.

Tycho Brahe soon discovered that his ignorance of the language and
unfamiliarity with the customs of the people caused him much
inconvenience. He therefore asked permission from the Emperor to be
allowed to remove to Prague. This request was readily granted, and a
suitable residence was provided for him in the city.

In the meantime his family, his large instruments, and other property,
having arrived at Prague, Tycho was soon comfortably settled in his new
home.

Though Tycho Brahe continued his astronomical observations, yet he could
not help feeling that he lived among a strange people; nor did the
remembrance of his sufferings and the cruel treatment he received at the
hands of his fellow-countrymen subdue the affection which he cherished
towards his native land. Pondering over the past, he became despondent
and low-spirited; a morbid imagination caused him to brood over small
troubles, and gloomy, melancholy thoughts possessed his mind--symptoms
which seemed to presage the approach of some serious malady. One
evening, when visiting at the house of a friend, he was seized with a
painful illness, to which he succumbed in less than a fortnight. He died
at Prague on October 24, 1601, when in his fifty-fifth year.

The Emperor Rudolph, when informed of Tycho Brahe's death, expressed his
deep regret, and commanded that he should be interred in the principal
church in the city, and that his obsequies should be celebrated with
every mark of honour and respect.

Tycho Brahe stands out as the most romantic and prominent figure in the
history of astronomy. His independence of character, his ardent
attachments, his strong hatreds, and his love of splendour, are
characteristics which distinguish him from all other men of his age.
This remarkable man was an astronomer, astrologer, and alchemist; but in
his latter years he renounced astrology, and believed that the stars
exercised no influence over the destinies of mankind.

As a practical astronomer, Tycho Brahe has not been excelled by any
other observer of the heavens. The magnificence of his observatory at
Huen, upon the equipment and embellishment of which it is stated he
expended a ton of gold; the splendour and variety of his instruments,
and his ingenuity in inventing new ones, would alone have made him
famous. But it was by the skill and assiduity with which he carried out
his numerous and important observations that he has earned for himself a
position of the most honourable distinction among astronomers. In his
investigation of the Lunar theory Tycho Brahe discovered the Moon's
_annual equation_, a yearly effect produced by the Sun's disturbing
force as the Earth approaches or recedes from him in her orbit. He also
discovered another inequality in the Moon's motion, called the
_variation_. He determined with greater exactness astronomical
refractions from an altitude of 45 deg. downwards to the horizon, and
constructed a catalogue of 777 stars. He also made a vast number of
observations on planets, which formed the basis of the 'Rudolphine
Tables,' and were of invaluable assistance to Kepler in his
investigation of the laws relating to planetary motion.

Tycho Brahe declined to accept the Copernican theory, and devised a
system of his own, which he called the 'Tychonic.' By this arrangement
the Earth remained stationary, whilst all the planets revolved round
the Sun, who in his turn completed a daily revolution round the Earth.
All the phenomena associated with the motions of those bodies could be
explained by means of this system; but it did not receive much support,
and after the Copernican theory became better understood it was given
up, and heard of no more.

We now arrive at the name of KEPLER, one of the very greatest of
astronomers, and a man of remarkable genius, who was the first to
discover the real nature of the paths pursued by the Earth and planets
in their revolution round the Sun. After seventeen years of close
observation, he announced that those bodies travelled round the Sun in
elliptical or oval orbits, and not in circular paths, as was believed by
Copernicus. In his investigation of the laws which govern the motions of
the planets he formulated those famous theorems known as 'Kepler's
Laws,' which will endure for all time as a proof of his sagacity and
surpassing genius. Prior to the discovery of those laws the Sun, though
acknowledged to be the centre of the system, did not appear to occupy a
central position as regards the motions of the planets; but Kepler, by
demonstrating that the planes of the orbits of all the planets, and the
lines connecting their apsides, passed through the Sun, was enabled to
assign the orb his true position with regard to those bodies.

JOHN KEPLER was born at Weil, in the Duchy of Wurtemberg, December 21,
1571. His parents, though of noble family, lived in reduced
circumstances, owing to causes for which they were themselves chiefly
responsible. In his youth Kepler suffered so much from ill-health that
his education had to be neglected. In 1586 he was sent to a monastic
school at Maulbronn, which had been established at the Reformation, and
was under the patronage of the Duke of Wurtemberg. Afterwards he studied
at the University of Tubingen, where he distinguished himself and took a
degree. Kepler devoted his attention chiefly to science and mathematics,
but paid no particular attention to the study of astronomy. Maestlin,
the professor of mathematics, whose lectures he attended, upheld the
Copernican theory, and Kepler, who adopted the views of his teacher,
wrote an essay in favour of the diurnal rotation of the Earth, in which
he supported the more recent astronomical doctrines. In 1594, a vacancy
having occurred in the professorship of astronomy at Gratz consequent
upon the death of George Stadt, Kepler was appointed his successor. He
did not seek this office, as he felt no particular desire to take up the
study of astronomy, but was recommended by his tutors as a man well
fitted for the post. He was thus in a manner compelled to devote his
time and talents to the science of astronomy. Kepler directed his
attention to three subjects--viz. 'the number, the size, and the motion
of the orbits of the planets.' He endeavoured to ascertain if any
regular proportion existed between the sizes of the planetary orbits, or
in the difference of their sizes, but in this he was unsuccessful. He
then thought that, by imagining the existence of a planet between Mars
and Jupiter, and another between Venus and Mercury, he might be able to
attain his object; but he found that this assumption afforded him no
assistance. Kepler then imagined that as there were five regular
geometrical solids, and five planets, the distances of the latter were
regulated by the size of the solids described round one another. The
discovery afterwards of two additional planets testified to the
absurdity of this speculation. A description of these extraordinary
researches was published, in 1596, in a work entitled 'Prodromus of
Cosmographical Dissertations; containing the cosmographical mystery
respecting the admirable proportion of the celestial orbits, and the
genuine and real causes of the number, magnitude, and periods of the
planets, demonstrated by the five regular geometrical solids.' This
volume, notwithstanding the fanciful speculations which it contained,
was received with much favour by astronomers, and both Tycho Brahe and
Galileo encouraged Kepler to continue his researches. Galileo admired
his ingenuity, and Tycho advised him 'to lay a solid foundation for his
views by actual observation, and then, by ascending from these, to
strive to reach the causes of things.' Kepler spent many years in these
fruitless endeavours before he made those grand discoveries in search of
which he laboured so long.

The religious dissensions which at this time agitated Germany were
accompanied in many places by much tumult and excitement. At Gratz the
Catholics threatened to expel the Protestants from the city. Kepler, who
was of the Reformed faith, having recognised the danger with which he
was threatened, retired to Hungary with his wife, whom he had recently
married, and remained there for near twelve months, during which time he
occupied himself with writing several short treatises on subjects
connected with astronomy. In 1599 he returned to Gratz and resumed his
professorship.

In the year 1600 Kepler set out to pay Tycho Brahe a visit at Prague, in
order that he might be able to avail himself of information contained in
observations made by Tycho with regard to the eccentricities of the
orbits of the planets. He was received by Tycho with much cordiality,
and stayed with him for four months at his residence at Benach, Tycho in
the meantime having promised that he would use his influence with the
Emperor Rudolph to have him appointed as assistant in his observatory.
On the termination of his visit Kepler returned to Gratz, and as there
was a renewal of the religious trouble in the city, he resigned his
professorship, from which he only derived a small income, and, relying
on Tycho's promise, he again journeyed to Prague, and arrived there in
1601. Kepler was presented to the Emperor by Tycho, and the post of
Imperial Mathematician was conferred upon him, with a salary of 100
florins a year, upon condition that he should assist Tycho in his
observatory. This appointment was of much value to Kepler, because it
afforded him an opportunity of obtaining access to the numerous
astronomical observations made by Tycho, which were of great assistance
to him in the investigation of the subject which he had chosen--viz. the
laws which govern the motions of the planets, and the form and size of
the planetary orbits.

As an acknowledgment of the Emperor's great kindness, the two
astronomers resolved to compute a new set of astronomical tables, and in
honour of his Majesty they were to be called the 'Rudolphine Tables.'
This project pleased the Emperor, who promised to defray the expense of
their publication. Logomontanus, Tycho's chief assistant, had entrusted
to him that portion of the work relating to observations on the stars,
and Kepler had charge of the part which embraced the calculations
belonging to the planets and their orbits. This important work had
scarcely been begun when the departure of Logomontanus, who obtained an
appointment in Denmark, and the death of Tycho Brahe in October 1601,
necessitated its suspension for a time. Kepler was appointed Chief
Mathematician to the Emperor in succession to Tycho--a position of
honour and distinction, and to which was attached a handsome salary,
that was paid out of the Imperial treasury. But owing to the continuance
of expensive wars, which entailed a severe drain upon the resources of
the country, the public funds became very low, and Kepler's salary was
always in arrear. This condition of things involved him in serious
pecuniary difficulties, and the responsibility of having to maintain an
increasing family added to his anxieties. It was with the greatest
difficulty that he succeeded in obtaining payment of even a portion of
his salary, and he was reduced to such straits as to be under the
necessity of casting nativities in order to obtain money to meet his
most pressing requirements.

In 1609 Kepler published his great work, entitled 'The New Astronomy;
or, Commentaries on the Motions of Mars.' It was by his observation of
Mars, which has an orbit of greater eccentricity than that of any of the
other planets, with the exception of Mercury, that he was enabled, after
years of patient study, to announce in this volume the discovery of two
of the three famous theorems known as Kepler's Laws. The first is, that
all the planets move round the Sun in elliptic orbits, and that the orb
occupies one of the foci. The second is, that the radius-vector, or
imaginary line joining the centre of the planet and the centre of the
Sun, describes equal areas in equal times. The third law, which relates
to the connection between the periodic times and the distances of the
planets, was not discovered until ten years later, when Kepler, in 1619,
issued another work, called the 'Harmonies of the World,' dedicated to
James I. of England, in which was contained this remarkable law. These
laws have elevated astronomy to the position of a true physical science,
and also formed the starting-point of Newton's investigations which led
to the discovery of the law of gravitation. Kepler's delight on the
discovery of his third law was unbounded. He writes: 'Nothing holds me.
I will indulge in my sacred fury. I will triumph over mankind by the
honest confession that I have stolen the golden vases of the Egyptians
to build up a tabernacle for my God far away from the confines of Egypt.
If you forgive me, I rejoice; if you are angry, I can bear it. The die
is cast; the book is written, to be read either now or by posterity I
care not which. It may well wait a century for a reader, as God has
waited six thousand years for an observer.'

When Kepler presented his celebrated book to the Emperor, he remarked
that it was his intention to make a similar attack upon the other
planets, and promised that he would be successful if his Majesty would
undertake to find the means necessary for carrying on operations. But
the Emperor had more formidable enemies to contend with nearer home than
Jupiter and Saturn, and no funds were forthcoming to assist Kepler in
his undertaking.

The chair of mathematics in the University of Linz having become vacant,
Kepler offered himself as a candidate for the appointment, which he was
anxious to obtain; but the Emperor Rudolph was averse to his leaving
Prague, and encouraged him to hope that the arrears of his salary would
be paid. But past experience led Kepler to have no very sanguine
expectations on this point; nor was it until after the death of Rudolph,
in 1612, that he was relieved from his pecuniary embarrassments.

On the accession of Rudolph's brother, Matthias, to the Austrian throne,
Kepler was reappointed Imperial Mathematician; he was also permitted to
hold the professorship at Linz, to which he had been elected. Kepler was
not loth to remove from Prague, where he had spent eleven years harassed
by poverty and other domestic afflictions. Having settled with his
family at Linz, Kepler issued another work, in 1618, entitled 'Epitome
of the Copernican Astronomy,' in which he gave a general account of his
astronomical observations and discoveries, and a summary of his opinions
with regard to the theories which in those days were the subject of
controversial discussion. Almost immediately after its publication it
was included by the Congregation of the Index, at Rome, in the list of
prohibited books. This occasioned Kepler considerable alarm, as he
imagined it might interfere with the sale of his works, or give rise to
difficulties in the issue of others. He, however, was assured by his
friend Remus that the action of the Papal authorities need cause him no
anxiety.

The Emperor Matthias died in 1619, and was succeeded by Ferdinand III.,
who not only retained Kepler in his office, but gave orders that all the
arrears of his salary should be paid, including those which accumulated
during the reign of Rudolph; he also expressed a desire that the
'Rudolphine Tables' should be published without delay and at his cost.
But other obstacles intervened, for at this time Germany was involved in
a civil and religious war, which interfered with all peaceful
vocations. Kepler's library at Linz was sealed up by order of the
Jesuits, and the city was for a time besieged by troops. This state of
public affairs necessitated a considerable delay in the publication of
the 'Tables.'

The 'Rudolphine Tables' were published at Ulm in 1627. They were
commenced by Tycho Brahe, and completed by Kepler, who made his
calculations from Tycho's observations, and based them upon his own
great discovery of the ellipticity of the orbits of the planets. They
are divided into four parts. The first and third parts contain
logarithmic and other tables for the purpose of facilitating
astronomical calculations; in the second are tables of the Sun, Moon,
and planets; and in the fourth are indicated the positions of one
thousand stars as determined by Tycho. Kepler made a special journey to
Prague in order to present the 'Tables' to the Emperor, and afterwards
the Grand Duke of Tuscany sent him a gold chain as an acknowledgment of
his appreciation of the completion of this great work.

Albert Wallenstein, Duke of Friedland, an accomplished scholar and a man
fond of scientific pursuits, made Kepler a most liberal offer if he
would take up his residence in his dominions. After duly considering
this proposal, Kepler decided to accept the Duke's offer, provided it
received the sanction of the Emperor. This was readily given, and
Kepler, in 1629, removed with his family from Linz to Sagan, in Silesia.
The Duke of Friedland treated him with great kindness and liberality,
and through his influence he was appointed to a professorship in the
University of Rostock. Though Kepler was permitted to retain the pension
bestowed upon him by the late Emperor Rudolph, he was unable after his
removal to Silesia to obtain payment of it, and there was a large
accumulation of arrears. In a final endeavour to recover the amount
owing to him he travelled to Ratisbon, and appealed to the Imperial
Assembly, but without success. The fatigue which Kepler endured on his
journey, combined with vexation and disappointment, brought on a fever,
which terminated fatally. He died on November 15, 1630, when in the
sixtieth year of his age, and was interred in St. Peter's churchyard,
Ratisbon.

Kepler was a man of indomitable energy and perseverance, and spared
neither time nor trouble in the accomplishment of any object which he
took in hand. In thinking over the form of the orbits of the planets, he
writes: 'I brooded with the whole energy of my mind on this
subject--asking why they are not other than they are--the number, the
size, and the motions of the orbits.' But many fanciful ideas passed
through Kepler's imaginative brain before he hit upon the true form of
the planetary orbits. In his 'Mysterium Cosmographicum' he asserts that
the five kinds of regular polyhedral solids, when described round one
another, regulated the distances of the planets and size of the
planetary orbits. In support of this theory he writes as follows: 'The
orbit of the Earth is the measure of the rest. About it circumscribe a
dodecahedron. The sphere including this will be that of Mars. About
Mars' orbit describe a tetrahedron; the sphere containing this will be
Jupiter's orbit. Round Jupiter's describe a cube; the sphere including
this will be Saturn's. Within the Earth's orbit inscribe an icosahedron;
the sphere inscribed in it will be Venus's orbit. In Venus inscribe an
octahedron; the sphere inscribed in it will be Mercury's.'

The above quotation is an instance of Kepler's wild and imaginative
genius, which ultimately led him to make those sublime discoveries
associated with planetary motion which are known as 'Kepler's Laws.'

He describes himself as 'troublesome and choleric in politics and
domestic matters;' but in his relations with scientific men he was
affable and pleasant. He showed no jealousy of a rival, and was always
ready to recognise merit in others; nor did he hesitate to acknowledge
any error of his own when more recent discoveries proved that he was
wrong.

Some of his works contain passages, written in a jocular strain,
indicative of a bright and cheerful temperament. The following
characteristic paragraph refers to the opinions of the Epicureans with
regard to the appearance of a new star, which they ascribed to a
fortuitous concourse of atoms: 'When I was a youth, with plenty of idle
time on my hands, I was much taken with the vanity, of which some grown
men are not ashamed, of making anagrams by transposing the letters of my
name written in Latin so as to make another sentence. Out of Ioannes
Keplerus came _Serpens in akuleo_ (a serpent in his sting); but not
being satisfied with the meaning of these words, and being unable to
make another, I trusted the thing to chance, and, taking out of a pack
of playing-cards as many as there were letters in the name, I wrote one
upon each, and then began to shuffle them, and at each shuffle to read
them in the order they came, to see if any meaning came of it. Now, may
all the Epicurean gods and goddesses confound this same chance, which,
although I have spent a good deal of time over it, never showed me
anything like sense, even from a distance. So I gave up my cards to the
Epicurean eternity, to be carried away into infinity; and it is said
they are still flying about there, in the utmost confusion, among the
atoms, and have never yet come to any meaning. I will tell those
disputants, my opponents, not my own opinion, but my wife's. Yesterday,
when weary with writing, and my mind quite dusty with considering these
atoms, I was called to supper, and a salad I had asked for was set
before me. "It seems, then," said I aloud, "that if pewter dishes,
leaves of lettuce, grains of salt, drops of water, vinegar and oil, and
slices of egg, had been flying about in the air from all eternity, it
might at last happen by chance that there would come a salad." "Yes,"
says my wife, "but not so nice and well dressed as this of mine is."'

Notwithstanding the frequent interruptions which, owing to various
reasons, retarded his labours, Kepler was able to bring to a successful
completion the numerous and important works upon which he was engaged
during his lifetime, the voluminous nature of which may be imagined when
it is stated that he published thirty-three separate works, besides
leaving behind twenty-two volumes of manuscript.

During his researches on the motions of Mars, Kepler discovered that the
planet sometimes travelled at an accelerated rate of speed, and at
another time its pace was diminished. At one time he observed it to be
in advance of the place where he calculated it should be found, and at
another time it was behind it. This caused him considerable perplexity,
and, feeling convinced in his mind that the form of the planet's orbit
could not be circular, he was compelled to turn his attention to some
other closed curve, by which those inequalities of motion could be
explained.

After years of careful observation and study, Kepler arrived at the
conclusion that the form of the planet's orbit is an ellipse, and that
the Sun occupies one of the foci. He afterwards determined that the
orbits of all the planets are of an elliptical form.

Having discovered the true form of the planetary orbits, Kepler next
endeavoured to ascertain the cause which regulates the unequal motion
that a planet pursues in its path. He observed that when a planet
approached the Sun its motion was accelerated, and as it receded from
him its pace became slower.

This he explained in his next great discovery by proving that an
imaginary line, or radius-vector, extending from the centre of the Sun
to the centre of the planet 'describes equal areas in equal times.' When
near the Sun, or at perihelion, a planet traverses a larger portion of
its arc in the same period of time than it does when at the opposite
part of its orbit, or when at aphelion; but, as the areas of both are
equal, it follows that the planet does not always maintain the same rate
of speed, and that its velocity is greatest when nearest the Sun, and
least when most distant from him.

By the application of his first and second laws Kepler was able to
formulate a third law. He found that there existed a remarkable
relationship between the mean distances of the planets and the times in
which they complete their revolutions round the Sun, and discovered
'that the squares of the periodic times are to each in the same
proportion as the cubes of the mean distances.' The periodic time of a
planet having been ascertained, the square of the mean distance and the
mean distance itself can be obtained. It is by the application of this
law that the distances of the planets are usually calculated.

These discoveries are known as Kepler's Laws, and are usually classified
as follows:--

1. 'The orbit described by every planet is an ellipse, of which the
centre of the Sun occupies one of the foci.

2. 'Every planet moves round the Sun in a plane orbit, and the
radius-vector, or imaginary line joining the centre of the planet and
the centre of the Sun, describes equal areas in equal times.

3. 'The squares of the periodic times of any two planets are
proportional to the cubes of their mean distances from the Sun.'[1]

These remarkable discoveries do not embrace all the achievements by
which Kepler has immortalised his name, and earned for himself the proud
title of 'Legislator of the Heavens;' he predicted transits of Mercury
and Venus, made important discoveries in optics, and was the inventor of
the astronomical telescope.

GALILEO GALILEI, the famous Italian astronomer and philosopher, and the
contemporary of Kepler and of Milton, was born at Pisa on February 15,
1564.

His father, who traced his descent from an ancient Florentine family,
was desirous that his son should adopt the profession of medicine, and
with this intention he entered him as a student at the University of
Pisa. Galileo, however, soon discovered that the study of mathematics
and mechanical science possessed a greater attraction for his mind,
and, following his inclinations, he resolved to devote his energies to
acquiring proficiency in those subjects.

In 1583 his attention was attracted by the oscillation of a brass lamp
suspended from the ceiling of the cathedral at Pisa. Galileo was
impressed with the regularity of its motion as it swung backwards and
forwards, and was led to imagine that the pendulum movement might prove
a valuable method for the correct measurement of time. The practical
application of this idea he afterwards adopted in the construction of an
astronomical clock.

Having become proficient in mathematics, Galileo, whilst engaged in
studying the writings of Archimedes, wrote an essay on 'The Hydrostatic
Balance,' and composed a treatise on 'The Centre of Gravity in Solid
Bodies.' The reputation which he earned by these contributions to
science procured for him the appointment of Lecturer on Mathematics at
the University of Pisa. Galileo next directed his attention to the works
of Aristotle, and made no attempt to conceal the disfavour with which he
regarded many of the doctrines taught by the Greek philosopher; nor had
he any difficulty in exposing their inaccuracies. One of these, which
maintained that the heavier of two bodies descended to the earth with
the greater rapidity, he proved to be incorrect, and demonstrated by
experiment from the top of the tower at Pisa that, except for the
unequal resistance of the air, all bodies fell to the ground with the
same velocity.

As the chief expounder of the new philosophy, Galileo had to encounter
the prejudices of the followers of Aristotle, and of all those who
disliked any innovation or change in the established order of things.
The antagonism which existed between Galileo and his opponents, who were
both numerous and influential, was intensified by the bitterness and
sarcasm which he imparted into his controversies, and the attitude
assumed by his enemies at last became so threatening that he deemed it
prudent to resign the Chair of Mathematics in the University of Pisa.

In the following year he was appointed to a similar post at Padua, where
his fame attracted crowds of pupils from all parts of Europe.

In 1611 Galileo visited Rome. He was received with much distinction by
the different learned societies, and was enrolled a member of the
Lyncaean Academy. In two years after his visit to the capital he
published a work in which he declared his adhesion to the Copernican
theory, and openly avowed his disbelief in the astronomical facts
recorded in the Scriptures. Galileo maintained that the sacred writings
were not intended for the purpose of imparting scientific information,
and that it was impossible for men to ignore phenomena witnessed with
their eyes, or disregard conclusions arrived at by the exercise of their
reasoning powers.

The champions of orthodoxy having become alarmed, an appeal was made to
the ecclesiastical authorities to assist in suppressing this recent
astronomical heresy, and other obnoxious doctrines, the authorship of
which was ascribed to Galileo.

In 1615, Galileo was summoned before the Inquisition to reply to the
accusation of heresy. 'He was charged with maintaining the motion of the
Earth and the stability of the Sun; with teaching this doctrine to his
pupils; with corresponding on the subject with several German
mathematicians; and with having published it, and attempted to reconcile
it to Scripture in his letters to Mark Velser in 1612.'

These charges having been formally investigated by the Inquisition,
Cardinal Bellarmine was authorised to communicate with Galileo, and
inform him that unless he renounced the obnoxious doctrines, and
promised 'neither to teach, defend, or publish them in future,' it was
decreed that he should be committed to prison. Galileo appeared next day
before the Cardinal, and, without any hesitation, pledged himself that
for the future he would adhere to the pronouncement of the Inquisition.

Having, as they imagined, silenced Galileo, the Inquisition resolved to
condemn the entire Copernican system as heretical; and in order to
effectually accomplish this, besides condemning the writings of Galileo,
they inhibited Kepler's 'Epitome of the Copernican System,' and
Copernicus's own work, 'De Revolutionibus Orbium Celestium.'

Whether it was that Galileo regarded the Inquisition as a body whose
decrees were too absurd and unreasonable to be heeded, or that he
dreaded the consequences which might have followed had he remained
obstinate, we know that, notwithstanding the pledges which he gave, he
was soon afterwards engaged in controversial discussion on those
subjects which he promised not to mention again.

On the accession of his friend Cardinal Barberini to the pontifical
throne in 1623, under the title of Urban VIII., Galileo undertook a
journey to Rome to offer him his congratulations upon his elevation to
the papal chair. He was received by his Holiness with marked attention
and kindness, was granted several prolonged audiences, and had conferred
upon him several valuable gifts.

Notwithstanding the kindness of Pope Urban and the leniency with which
he was treated by the Inquisition, Galileo, having ignored his pledge,
published in 1632 a book, in dialogue form, in which three persons were
supposed to express their scientific opinions. The first upheld the
Copernican theory and the more recent philosophical views; the second
person adopted a neutral position, suggested doubts, and made remarks of
an amusing nature; the third individual, called Simplicio, was a
believer in Ptolemy and Aristotle, and based his arguments upon the
philosophy of the ancients.

As soon as this work became publicly known, the enemies of Galileo
persuaded the Pope that the third person held up to ridicule was
intended as a representation of himself--an individual regardless of
scientific truth, and firmly attached to the ideas and opinions
associated with the writings of antiquity.

Almost immediately after the publication of the 'Dialogues' Galileo was
summoned before the Inquisition, and, notwithstanding his feeble health
and the infirmities of advanced age, he was, after a long and tedious
trial, condemned to abjure by oath on his knees his scientific beliefs.

'The ceremony of Galileo's abjuration was one of exciting interest and
of awful formality. Clothed in the sackcloth of a repentant criminal,
the venerable sage fell upon his knees before the assembled cardinals,
and, laying his hand upon the Holy Evangelists, he invoked the Divine
aid in abjuring, and detesting, and vowing never again to teach the
doctrines of the Earth's motion and of the Sun's stability. He pledged
himself that he would nevermore, either in words or in writing,
propagate such heresies; and he swore that he would fulfil and observe
the penances which had been inflicted upon him.' 'At the conclusion of
this ceremony, in which he recited his abjuration word for word and then
signed it, he was conveyed, in conformity with his sentence, to the
prison of the Inquisition.'[2]

Galileo's sarcasm, and the bitterness which he imparted into his
controversies, were more the cause of his misfortunes than his
scientific beliefs. When he became involved in difficulties he did not
possess the moral courage to enable him to abide by the consequences of
his acts; nor did he care to become a martyr for the sake of science,
his submission to the Inquisition having probably saved him from a fate
similar to what befell Bruno. Though it would be impossible to justify
Galileo's want of faith in his dealings with the Inquisition, yet one
cannot help sympathising deeply with the aged philosopher, who, in this
painful episode of his life, was compelled to go through the form of
making a retractation of his beliefs under circumstances of a most
humiliating nature.

But the persecution of Galileo did not delay the progress of scientific
inquiry nor retard the advancement of the Copernican theory, which,
after the discovery by Newton of the law of gravitation, was universally
adopted as the true theory of the solar system.

Ferdinand, Duke of Tuscany, having exerted his influence with Pope Urban
on behalf of Galileo, he was, after a few days' incarceration, released
from prison, and permission was given him to reside at Siena, where he
remained for six months. He was afterwards allowed to return to his
villa at Arcetri, and, though regarded as a prisoner of the Inquisition,
was permitted to pursue his studies unmolested for the remainder of his
days.

Galileo died at Arcetri on January 8, 1642, when in the seventy-eighth
year of his age.

Though not the inventor, he was the first to construct a refracting
telescope and apply it to astronomical research. With this instrument
he made a number of important discoveries which tended to confirm his
belief in the truthfulness of the Copernican theory.

On directing his telescope to the Sun, he discovered movable spots on
his disc, and concluded from his observation of them that the orb
rotated on his axis in about twenty-eight days. He also ascertained that
the Moon's illumination is due to reflected sunlight, and that her
surface is diversified by mountains, valleys, and plains.

On the night of January 7, 1610, Galileo discovered the four moons of
Jupiter. This discovery may be regarded as one of his most brilliant
achievements with the telescope; and, notwithstanding the improvement in
construction and size of modern instruments, no other satellite was
discovered until near midnight on September 9, 1892, when Mr. E. E.
Barnard, with the splendid telescope of the Lick Observatory, added
'another gem to the diadem of Jupiter.'

The phases of Venus and Mars, the triple form of Saturn, and the
constitution of the Milky Way, which he found to consist of a countless
multitude of stars, were additional discoveries for our knowledge of
which we are indebted to Galileo and his telescope. Galileo made many
other important discoveries in mechanical and physical science. He
detected the law of falling bodies in their accelerated motion towards
the Earth, determined the parabolic law of projectiles, and
demonstrated that matter, even if invisible, possessed the property of
weight.

In these pages a short historical description is given of the progress
made in astronomical science from an early period to the time in which
Milton lived. The discoveries of Copernicus, Kepler, and Galileo had
raised it to a position of lofty eminence, though the law of
gravitation, which accounts for the form and permanency of the planetary
orbits, still remained undiscovered. Theories formerly obscure or
conjectural were either rejected or elucidated with accuracy and
precision, and the solar system, having the Sun as its centre, with his
attendant family of planets and their satellites revolving in majestic
orbits around him, presented an impressive spectacle of order, harmony,
and design.