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CONTENTS.
CHAPTER I.
THE SUN, THE CENTRAL ORB OF THE PLANETARY
SYSTEM.
DISCOVERIES OF THE ANCIENTS.-The Source of Life and Light and
Heat.-The Sun's Motion among the Stars.-His Orbit circular.—
Length of the Year.-Inequality of the Sun's Motion.-Explained
by Hipparchus.-Solar Eclipses.-Their First Prediction.
DISCOVERIES OF THE MODERNS.-The Sun's Distance.-His Hori-
zontal Parallax.-Importance of this Element.-Measured by the
transit of Venus.-The Sun's actual Diameter and real Magni-
tude. - His Rotation.-The Solar Spots. -Their Periodicity.—
Speculations as to the Physical Constitution of the Sun...... Page 1
CHAPTER II.
MERCURY, THE FIRST PLANET IN THE ORDER OF DISTANCE
FROM THE SUN.
-
Its Early Discovery.-Difficult to be distinguished from the Stars.—
Elongations.-Motion Direct and Retrograde. Sometimes Sta-
tionary.-Nature of the Orbit. -Variation in the Elongation ex-
plained. The Nodes. Transit of Mercury.
Inclination of
Mercury's Orbit.-Mean Distance from the Sun.-Conjunctions.-
Phases.-Diameter and Volume
Page 26
CHAPTER III.
VENUS, THE SECOND PLANET IN THE ORDER OF DISTANCE
The First Planet discovered.-Mode of its Discovery.-Her Elonga-
tions.-Morning and Evening Star.-A Satellite of the Sun.-Her
Superior and Inferior Conjunctions.-Her Stations.-Direct and
Retrograde Motions.-These Phenomena indicate a Motion of the
Earth.-Transits of Venus.-Inclination of the Orbit of Venus to
the Ecliptic.-Her Nodes.-Intervals of her Transits.-Knowledge
of the Ancients.-Phases of Venus.-Her Elongations unequal.-No
Satellite yet discovered.-Sun's Light and Heat at Venus.-Her
Atmosphere Page 3
...
CHAPTER IV.
THE EARTH AND ITS SATELLITE: THE THIRD PLANET IN
THE ORDER OF DISTANCE FROM THE SUN.
The Earth the apparent Centre of Motion.-To all the senses it is at
rest. The Centre of the Motions of the Sun and Moon.-Explana-
tion of the Acceleration of the Orbitual Motion of the Sun and
Moon.-Ptolemy's Epicycles.-The Explanation of Copernicus.-
The Sun the Centre of Planetary Motion.-The Earth one of the
Planets. Objections to this Hypothesis.-The Answer.-System of
Jupiter discovered by the Telescope.-The Old system superseded
by the New. The Figure and Magnitude of the Earth.-How
determined. The Earth's Motions.-Rotation and Revolution.-A
Unit of Time furnished by the Earth's Period of Rotation.-Earth's
Orbitual Motion.-Vernal Equinox.-Perihelion of Earth's Orbit.—
Its Period of Revolution.-Solar and Sidereal Time.
THE MOON.-Revolution in her Orbit.-Her Phases.-Earth's Line.-
Eccentricity of her Orbit.--Revolution of her Apogee.-Inclination
of her Orbit.-Moon's Parallax and Distance.-Her Physical Con-
stitution.-Centre of Gravity and Centre of Figure......
Page 40
CHAPTER V.
MARS, THE FOURTH PLANET IN THE ORDER OF DISTANCE
Phenomena of Mars difficult to explain with the Earth as the Centre
of Motion.-Copernican System applied.-Epicycle of Mars.-Better
instruments and more accurate observations.-Tycho and Kepler.-
Kepler's method of investigation.-Circles and Epicycles exhausted.
-The Ellipse.-Its Properties.-The Orbit of Mars an Ellipse.-
Kepler's Laws.-Elliptical Orbits of the Planets.-The Elements of
the Planetary Orbits explained.-How these Elements are obtained.
-Kepler's third Law.-Value of this Law.-The Physical Aspect of
Mars. Snow-Zones. - Rotation of the Planet. Diameter and
Volume.-Speculation as to its Climate and Colour
Page 74
CHAPTER VI.
THE ASTEROIDS: A GROUP OF SMALL PLANETS, THE FIFTH
IN THE ORDER OF DISTANCE FROM THE SUN.
The Interplanetary Spaces.-Kepler's Speculations.-Great Interval
between Mars and Jupiter.-Bode's Empirical Law.-Conviction
that a Planet existed between Mars and Jupiter.-Congress of
Astronomers.-An Association organized to search for the Planet.
-Discovery of Ceres.-Lost in the solar beams.-Rediscovered by
Gauss.-The New Order disturbed by the Discovery of Pallas.—
Oller's Hypothesis.-Discovery of Juno and Vesta.-The search
ceases.- Renewed in 1845. Many Asteroids discovered.-Their
Magnitude, Size, and probable Number....
CHAPTER VII.
Page 94
JUPITER, ATTENDED BY FOUR MOONS, THE SIXTH PLANET
Arc of Retrogradation.-Stationary Point.-Distance of the Planet
determined.-Periodic Time.-Synodical Revolution gives the Side-
real. Surface of Jupiter as given by the Telescope.-Period of
Rotation. Diameter. -Volume. Mean Distance. Amount of
Light and Heat.-Figure of Jupiter.-Equatorial and Polar Diame-
ters.-Discovery of the Four Moons by Galileo.-Effect on the
Copernican Theory.-Jupiter's Nocturnal Heavens.
THE SATELLITES OF JUPITER.-How discovered.—Their Magnitude.-
Form of their Orbits.-Period of Revolution.-Eclipses.-Transits.
-Occultations.-Velocity of Light discovered.-Terrestrial Longi-
tude.-Rotation of these Moons on an Axis
CHAPTER VIII.
Page 101
SATURN, THE SEVENTH PLANET IN THE ORDER OF DIS-
TANCE FROM THE SUN, SURROUNDED BY CONCENTRIC
RINGS, AND ATTENDED BY EIGHT SATELLITES.
------
The most distant of the Old Planets.-Its Light faint, but steady.—
Synodical Revolution. The Sidereal Revolution. Advances in
Telescopic Discovery.-Galileo announces Saturn to be Triple.-
Huygens discovers the Ring.-Division of the Ring into Two.—
Cassini announces the Outer Ring the brighter.-Multiple Division.
-Shadow of the Planet on the Ring.-Belts and Spots.-Period of
Rotation of the Planet and Ring.-Disappearance of the Ring
explained. The Dusky Ring.
SATELLITES OF SATURN.-By whom discovered.-Eight in number.→
Their Distances and Periods.-Saturn's Orbit the boundary of the
Planetary System, as known to the Ancients
CHAPTER IX.
THE LAWS OF MOTION AND GRAVITATION.
Page 119
The demands of Formal Astronomy.-Those of Physical Astronomy.
-Synopsis of the Discoveries already made.-Questions remaining
to be answered.-Inquiry into Causes.-The Laws of Motion de-
manded.-Rectilineal Motion.-Falling Bodies.-Law of Descent.—
Motion of Projectiles.-Curvilinear Motion.-First Law of Motion.
-Second Law of Motion.-Momentum of Moving Bodies.-Motion
on an Inclined Plane.-The Centrifugal Force.-Central Attraction.
-Gravitation.-Laws of Motion applied to the Planets.-Questions
propounded in Physical Astronomy.-Newton's Order of Investi-
gation. His Assumed Law of Gravitation.-Outline of his Demon-
stration.-Its Importance and Consequences.-The Law of Gravita-
tion embraces all the Planets and their Satellites.-Gravitation
resides in every particle of Matter
CHAPTER X.
Page 127
THE LAWS OF MOTION AND GRAVITATION APPLIED TO
A SYSTEM OF THREE REVOLVING BODIES.
A System of two Bodies.-Quantities required in its Investigation.—
Five in number.-Sun and Earth.-Sun, Earth, and Moon, as
Systems of Three Bodies. - The Sun supposed Stationary.
Changed Figure of the Moon's Orbit. Sun Revolving changes
the Position of the Moon's Orbit.—Solar Orbit Elliptical.-Effects
resulting from the Inclination of the Moon's Orbit.-Moon's Motion
above and below the Plane of the Ecliptic.-Revolution of the Line
of Nodes.-Sun, Earth, and Planet, as the Three Bodies.-Per-
turbations destroy the Rigour of Kepler's Laws.-Complexity thus
introduced. Infinitesimal Analysis.-Difference between Geome-
trical and Analytical Reasoning
Page 151
CHAPTER XI.
INSTRUMENTAL ASTRONOMY.
Method for obtaining the Mass of the Sun.-For getting the Mass
of a Planet with a Satellite.-For Weighing a Planet having no
Satellite.-For Weighing the Satellites.-Planetary Distances to be
measured.-Intervals between Primaries and their Satellites to be
obtained.-Intensity and Direction of the Impulsive Forces to be
determined. These Problems all demand Instrumental Measures.
-Differential Places.-Absolute Places.-The Transit-Instrument.
-Adjustments.-Instrumental Errors.-Corrections due to various
Causes.-American Method of Transits.-Meridian-Circle. - The
Declinometer
Page 164
CHAPTER XII.
URANUS, THE EIGHTH PLANET IN THE ORDER OF
DISTANCE FROM THE SUN.
Accidentally discovered by Sir William Herschel.-Announced as a
Comet.-Its Orbit proved it to be a Superior Planet.-The Ele-
ments of its Orbit obtained.-Arc of Retrogradation.-Period of
Revolution. Figure of the Planet.-Inclination of its Orbit.-Six
Satellites announced by the elder Herschel.-Four of these now
recognized. Their Orbital Planes and Directions of Revolution
Anomalous.-Efforts made to Tabulate the Places of Uranus unsuc-
cessful. This leads to the Discovery of a New Exterior Planet Page 203
CHAPTER XIII.
NEPTUNE, THE NINTH AND LAST KNOWN PLANET IN THE
ORDER OF DISTANCE FROM THE SUN.
Uranus discovered by Accident.-Ceres by Research with the Tele-
scope.Rediscovered by Mathematical Computation. - The Per-
turbations of Uranus.-Not due to any known Cause.-Assumed to
arise from an Exterior Planet.-Nature of the Examination to find
the Unknown Planet.-Undertaken at the same time by two Com-
puters.-Computation assigns a Place to the Unknown Planet.-
Discovered by the Telescope.-Discoveries resulting.-A Satellite
detected.-The Mass of Neptune thus determined.-Neptune's Orbit
the Circumscribing Boundary of the Planetary System ...... Page 211
CHAPTER XIV.
THE COMETS.
Objects of Dread in the Early Ages.-Comets obey the Law of Gravi-
tation and revolve in some one of the Conic Sections.-Character-
istics of these Curves.-Comet of 1680 studied by Newton.-Comet
of 1682 named " Halley's Comet." - Its History. - Its Return
predicted. —Perihelion Passage computed. —Passes its Perihelion