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INTRODUCTION

CONTENTS.

CHAP. I.

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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 1dea of the Distance of the Stars. - Definitions.

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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.

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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.

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CHAP. IV.

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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CHAP. V.

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.

CHAP. VI.

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Page 184

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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.

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213

CHAP. VII.

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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CHAP. VIII.

OF THE SOLAR SYSTEM.

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.

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CHAP. IX.

OF THE SATELLITES.

243

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.
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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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Page 300

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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. XII.

OF SIDEREAL ASTRONOMY.

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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
Nebulous Stars. Annular and Planetary

of Stars. Of Nebulæ.

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Nebulæ.-Zodiacal Light.

CHAP. XIII.

OF THE CALENDAR.

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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'

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