TREATISE ON ASTRONOMY.

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SIR JOHN F. W. HERSCHEL, KN GUELP.

FRS. LEE. M.R.IN FRAS. I. GS. MCUPS.

CORRESPONDENT OF THE ROYAL ACADEMY OF SCIENCES OF PARIS,

AND OTHER FOREIGN SCIENTIFIC INSTITUTIONS.

PUBLISHED BY LONGMAN, REES, ORME, BROWN, GREEN & LONGMAN, PATERNOSTER ROW,

AND JOHN TAYLOR, UPPER GOWER STREET.

INTRODUCTION

CONTENTS.

CHAP. L

Page 1

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

CHAP. II.

9

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 destined 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.

CHAP. III.

OF GEOGRAPHY.

64

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 Pendulum. Gravity to a Spheroid. Other Effects of Earth's Rotation. Trade Winds. Determination of Geographical Positions. Of Latitudes. Of Longitudes. -Conduct of a Trigonometrical Survey. - Of Maps.Projections of the Sphere.. Measurement of Heights by the Barometer.

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107

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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 Latitudes and Longitudes. - Precession of the Equinoxes. - Nutation. — Aberration. Uranographical Problems. 157

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 Description of Areas. Parallax of the Sun. Its Distance and Magnitude. 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

CHAP. VI.

Of the Moon. -Its Sidereal Period. Its apparent Diameter. — Its Parallax, Distance, and real Diameter. - First Approximation to its Orbit. — An Ellipse about the Earth in the Focus. - Its Excentricity and Inclination. 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.- Libration.Appearance of the Earth from it.

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

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. — Kepler's Laws and their Interpretation.- Elliptic Elements of a Planet's Orbit. Its Heliocentric and Geocentric Place. - Bode's Law of Planetary Distances. The four Ultra-Zodiacal Planets. - Physical Peculiarities observable in each of the Planets.

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 Jupiter's Satellites. Their Eclipses, &c. - Velocity of Light discovered by their Means.-Satellites of Saturn-Of Uranus. 288

CHAP. X.

OF COMETS.

Great Number of recorded Comets.-The Number of unrecorded probably 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. — Periodic Return of certain Comets. — Halley's. - Encke's. - Biela's. — Dimensions of Comets. - Their Resistance by the Ether, gradual Decay, and possible Dispersion in Space.

CHAP. XI.

OF PERTURBATIONS.

Page 300

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 Equinoxes. 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. - Secular 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.

CHAP. XII.

OF SIDEREAL ASTRONOMY.

312

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. - Temporary 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.

CHAP. XIII.

OF THE CALENDAR.

372

408