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INTRODUCTION

CHAP. I.

General Notions. - Form and Magnitude of the Earth. - Horizon and its
Dip. -The Atmosphere. - Refraction. - Twilight. Appearances re-
sulting from Diurnal Motion. -Parallax. - First Step towards forming
an idea of the Distance of the Stars.- Definitions.

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CONTENTS.

CHAP. II.

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Of the Nature of Astronomical Instruments and Observations in general.
-Of Sidereal and Solar Time. Of the Measurement of Time. -
Clocks, Chronometers, the Transit Instrument. Of the Measurement
of Angular Intervals. — Application of the Telescope to Instruments de-
stined to that Purpose. Of the Mural Circle.- Determination of Polar
and Horizontal Points. - The Level.- Plumb Line.-Artificial Horizon.
Collimator.-Of Compound Instruments with Co-ordinate Circles, the
Equatorial. -Altitude and Azimuth Instrument. Of the Sextant and
" Reflecting Circle. - Principle of Repetition.

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CHAP. III.

OF GEOGRAPHY.

Of the Figure of the Earth. Its exact Dimensions. - Its Form that of
Equilibrium modified by Centrifugal Force. - Variation of Gravity on
its Surface. Statical and Dynamical Measures of Gravity. The Pen-
dulum. - Gravity to a Spheroid. - Other Effects of Earth's Rotation. —
Trade Winds. - Determination of Geographical Positions. — Of Lati-
tudes. Of Longitudes. — Conduct of a Trigonometrical Survey. - Of
Maps.-Projections of the Sphere. — Measurement of Heights by the
Barometer.

107

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CHAP. IV.

Page 1

OF URANOGRAPHY.

Construction of Celestial Maps and Globes by Observations of Right
Ascension and Declination. - Celestial Objects distinguished into Fixed
and Erratic. Of the Constellations. - Natural Regions in the Heavens.
-The Milky Way.-The Zodiac. Of the Ecliptic. - Celestial Lati-
tudes and Longitudes. Precession of the Equinoxes. Nutation.
Aberration. Uranographical Problems.

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157

OF THE SUN'S MOTION.

Apparent Motion of the Sun not uniform.—Its apparent Diameter also
variable. - Variation of its Distance concluded. Its apparent Orbit an
Ellipse about the Focus. - Law of the Angular Velocity.- Equable De-
scription of Areas. - Parallax of the Sun. Its Distance and Mag-
nitude. - Copernican Explanation of the Sun's apparent Motion.
Parallelism of the Earth's Axis. The Seasons. Heat received from
the Sun in different Parts of the Orbit.

Page 184

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CHAP. V.

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CHAP. VI.

Of the Moon. Its Sidereal Period. Its apparent Diameter. Its Paral-
lax, Distance, and real Diameter. - First Approximation to its Orbit. -
An Ellipse about the Earth in the Focus. -Its Excentricity and Inclina-
tion. Motion of the Nodes of its Orbit. Occultations.
- - Solar
Eclipses.-Phases of the Moon. Its synodical Period.- Lunar Eclipses.
Motion of the Apsides of its Orbit. - Physical Constitution of the
Moon. Its Mountains. Atmosphere. - Rotation on Axis. - Libra-
tion. Appearance of the Earth from it.

213

CHAP. VIII.

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CHAP. VII.

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Of Terrestrial Gravity. -Of the Law of universal Gravitation. - Paths of
Projectiles; apparent - real. The Moon retained in her Orbit by Gra.
vity. Its Law of Diminution. - Laws of Elliptic Motion. — Orbit of
the Earth round the Sun in accordance with these Laws. - Masses of
the Earth and Sun compared. - Density of the Sun. - Force of Gravity
at its Surface. Disturbing Effect of the Sun on the Moon's Motion. 232

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OF THE SOLAR SYSTEM.

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Apparent Motions of the Planets. -Their Stations and Retrogradations.
-The Sun their natural Center of Motion. Inferior Planets. - Their
Phases, Periods, &c. - Dimensions and Form of their Orbits. - Transits
across the Sun. - Superior Planets, their Distances, Periods, &c. — Kep-
ler's Laws and their Interpretation. Elliptic Elements of a Planet's
Orbit. Its Heliocentric and Geocentric Place. - Bode's Law of Pla-
netary Distances. The four Ultra-Zodiacal Planets. Physical Pecu-
liarities observable in each of the Planets.
243

CHAP. IX.

OF THE SATELLITES.

Of the Moon, as a Satellite of the Earth.. General Proximity of Satellites
to their Primaries, and consequent Subordination of their Motions. -
Masses of the Primaries concluded from the Periods of their Satellites.
-Maintenance of Kepler's Laws in the secondary Systems. — Of Jupi-
ter's Satellites.-Their Eclipses, &c. - Velocity of Light discovered by
their Means.-Satellites of Saturn-Of Uranus.
288

CONTENTS.

CHAP. X.

OF COMETS.

Great Number of recorded Comets. - The Number of unrecorded pro-
bably much greater.- Description of a Comet. Comets without Tails.
-Increase and Decay of their Tails. - Their Motions. Subject to the
general Laws of Planetary Motion. — Elements of their Orbits. - Peri-
odic Return of certain Comets. - Halley's. - Encke's. — Biela's. — Di-
mensions of Comets. - Their Resistance by the Ether, gradual Decay,
and possible Dispersion in Space.

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CHAP. XI.

OF PERTURBATIONS.

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Subject propounded. - Superposition of small Motions. - Problem of Three
Bodies. Estimation of disturbing Forces. Motion of Nodes. -
Changes of Inclination. — Compensation operated in a whole Revolution
of the Node. - Lagrange's Theorem of the Stability of the Inclinations.
Change of the Obliquity of the Ecliptic. Precession of the Equi-
noxes. Nutation. - Theorem respecting forced Vibrations. — Of the
Tides. Variation of Elements of the Planet's Orbits- Periodic and
Secular. - Disturbing Forces considered as Tangential and Radial. —
Effects of Tangential Force:-1st, in Circular Orbits; 2d, in Elliptic.-
Compensations effected. Case of near Commensurability of Mean
Motions. The great Inequality of Jupiter and Saturn explained. - The
long Inequality of Venus and the Earth. - Lunar Variation. - Effect
of the Radial Force.. Mean Effect of the Period and Dimensions of the
Disturbed Orbit. -Variable Part of its Effect. - Lunar Evection. Secu-
lar Acceleration of the Moon's Motion. - Permanence of the Axes and
Periods. — Theory of the secular Variations of the Excentricities and
Perihelia. - - Motion of the Lunar Apsides. Lagrange's Theorem of
the Stability of the Excentricities. - Nutation of the Lunar Orbit. —
Perturbations of Jupiter's Satellites.
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CHAP. XIII.

OF THE CALENDAR.

CHAP. XII.

OF SIDEREAL ASTRONOMY.

Of the Stars generally. - Their Distribution into Classes according to
their apparent Magnitudes. -
-Their apparent Distribution over the
Heavens. - Of the Milky Way. - Annual Parallax. - Real Distances,
probable Dimensions, and Nature of the Stars. - Variable Stars. - Tem-
porary Stars. - Of Double Stars.-Their Revolution about each other
in elliptic Orbits. — Extension of the Law of Gravity to such Systems.
- Of coloured Stars.- Proper Motion of the Sun and Stars.-Systematic
Aberration and Parallax. Of compound Sidereal Systems.
- Clusters
of Stars. Of Nebulæ. - Nebulous Stars. Annular and Planetary
Nebula.-Zodiacal Light.

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Synoptic Table of the Elements of the Solar System

Synoptic Table of the Elements of the Orbits of the Satellites, so'

far as they are known
I. The Moon

II. Satellites of Jupiter

III. Satellites of Saturn

IV. Satellites of Uranus

INDEX

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