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General notions. Apparent and real motions. Shape and size of the Earth.
The horizon and its dip. The atmosphere. Refraction. Twilight.
Appearances resulting from diurnal motion. From change of station in
general. Parallactic motions. Terrestrial parallax. That of the stars
insensible. First step towards forming an idea of the distance of the stars.
Copernican view of the Earth's motion. Relative motion. Motions partly
real, partly apparent. Geocentric astronomy, or ideal reference of pheno-
mena to the Earth's centre as a common conventional station.
CHAPTER II.
25
Terminology and elementary geometrical conceptions and relations. Ter-
minology relating to the globe of the Earth-to the celestial sphere.
Celestial perspective
CHAPTER III.
68
Of the nature of astronomical instruments and observations in general.
Of sidereal and solar time. Of the measurements of time. Clocks, chro-
nometers. Of astronomical measurements. Principle of telescopic sights
to increase the accuracy of pointing. Simplest application of this princi-
ple. The transit instrument. Of the measurement of angular intervals.
Methods of increasing the accuracy of reading. The vernier. The
microscope. Of the mural circle. The Meridian circle. Fixation of
polar and horizontal points. The level, plumb-line, artificial horizon.
Principle of collimation. Collimators of Rittenhouse, Kater, and Benzen-
berg. Of compound instruments with co-ordinate circles. The equatorial,
altitude, and azimuth instrument. Theodolite. Of the sextant and
reflecting circle. Principle of repetition. Of micrometers. Parallel wire
micrometer. Principle of the duplication of images. The heliometer.
Double refracting eye-piece. Variable prism micrometer. Of the position.
micrometer 84
CHAPTER IV.
OF GEOGRAPHY.
Of the figure of the Earth. Its exact dimensions. Its form that of equili-
brium 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 the 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
CHAPTER V.
OF URANOGRAPHY.
Page 129
Construction of celestial maps and globes by observation 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. Pre-
cession of the Equinoxes. Nutation. Aberration. Refraction. Parallax.
Summary view of the Uranographical corrections . 176
CHAPTER VI.
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. Mean and true longitudes of the Sun. Equation of the centre.
Sidereal, tropical, and anomalistic years. Physical constitution of the
Sun. Its spots. Facula. Probable nature and cause of the spots.
Atmosphere of the Sun. Its supposed clouds. Temperature at its
surface. Its expenditure of heat. Terrestrial effect of solar radiation
CHAPTER VII.
205
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 its nodes and apsides. Of occultations and solar eclipses generally.
Limits within which they are possible. They prove the Moon to be an
opaque solid. Its light derived from the Sun. Its phases. Synodic
revolution or lunar month. Of eclipses more particularly. Their pheno-
mena. Their periodical recurrence. Physical constitution of the Moon.
Its mountains and other superficial features. Indications of former
volcanic activity. Its atmosphere. Climate. Radiation of heat from
its surface. Rotation on its own axis. Libration. Appearance of the
Earth from it 234
CHAPTER VIII.
Of terrestrial gravity. Of the law of universal gravitation. Paths of pro-
jectiles, apparent, real. The Moon retained in her orbit by gravity. 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. Disturb-
ing effect of the Sun on the Moon's motion
257
CONTENTS.
9
CHAPTER IX.
OF THE SOLAR SYSTEM.
Apparent motions of the planets. Their stations and retrogradations. The
Sun their natural centre of motion. Inferior planets. Their phases,
periods, etc. Dimensions and form of their orbits. Transits across the
Sun. Superior planets. Their distances, periods, etc. Kepler's laws
and their interpretation. Elliptic elements of a planet's orbit. Its helio-
centric and geocentric place. Empirical law of planetary distances;
violated in the case of Neptune. The ultra-zodiacal planets. Physical
peculiarities observable in each of the planets
CHAPTER X.
OF THE SATELLITES.
Page 267
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. Main-
tainance of Kepler's laws in the secondary systems. Of Jupiter's satel-
lites; their eclipses, etc. Velocity of light discovered by their means.
Satellites of Saturn-of Uranus-of Neptune.
CHAPTER XI.
OF COMETS.
311
Great number of recorded comets. The number of those unrecorded pro-
bably much greater. General description of a comet. Comets without
Their extreme tenuity. Their probable
tails, or with more than one.
structure. Motions conformable to the law of gravity. Actual dimen-
sions of comets. Periodical return of several. Halley's comet. Other
Its
ancient comets probably periodic. Encke's comet-Biela's-Faye's—
Great comet of 1843.
Lexell's-De Vico's-Brorsen's-Peter's.
Great interest at present
probable identity with several older comets.
Remarks on cometary
attached to cometary astronomy, and its reasons.
orbits in general .
PART II.
OF THE PLANETARY PERTURBATIONS.
CHAPTER XII.
325
Subject propounded. Problem of three bodies. Superposition of small
motions. Estimation of the disturbing force. Its geometrical representa-
Resolution into rect-
tion. Numerical estimation in particular cases.
angular components. Radial, transversal, and orthogonal disturbing
forces. Normal and tangential. Their characteristic effects. Effects of
the orthogonal force. Motion of the nodes. Conditions of their advance
and recess.
Cases of an exterior planet disturbed by an interior. The
In every case the node of the disturbed orbit recedes on the
plane of the disturbing on an average. Combined effect of many such
disturbances. Motion of the Moon's nodes. Change of inclination.
Conditions of its increase and diminution. Average effect in a whole revo-
lution. Compensation in a complete revolution of the nodes. Lagrange's
reverse case.
theorem of the stability of the inclinations of the planetary orbits. Change
of obliquity of the ecliptic. Precession of the equinoxes explained. Nuta-
tion. Principle of forced vibrations
CHAPTER XIII.
THEORY OF THE AXES, PERIHELIA, AND EXCENTRICITIES.
Page 360
Variation of elements in general. Distinction between periodic and secular
variations. Geometrical expression of tangential and normal forces.
Variation of the Major Axis produced only by the tangential force.
Lagrange's theorem of the conservation of the mean distances and periods.
Theory of the Perihelia and excentricities. Geometrical representation
of their momentary variations. Estimation of the disturbing forces in
nearly circular orbits. Application to the case of the Moon. Theory of
the lunar apsides and excentricity. Experimental illustration. Applica-
tion of the foregoing principles to the Planetary theory. Compensation
in orbits very nearly circular. Effects of ellipticity. General results.
Lagrange's theorem of the stability of the excentricities. 392
CHAPTER XIV.
Of the inequalities independent of the excentricities. The Moon's variation
and parallactic inequality. Analogous planetary inequalities. Three
cases of Planetary perturbation distinguished. Of inequalities dependent
on the excentricities. Long inequality of Jupiter and Saturn. Law of
reciprocity between the periodical variations of the elements of both
planets. Long inequality of the Earth and Venus. Variation of the
epoch. Inequalities incident on the epoch affecting the mean motion.
Interpretation of the constant part of these inequalities. Annual equation
of the Moon. Her secular acceleration. Lunar inequalities due to the
action of Venus. Effect of the spheroidal figure of the Earth and other
planets on the motions of their satellites. Of the tides. Masses of dis-
turbing bodies deducible from the perturbations they produce. Mass of
Moon, and of Jupiter's satellites, how ascertained. Perturbations of
Uranus resulting in the discovery of Neptune
PART III.
OF SIDEREAL ASTRONOMY.
CHAPTER XV.
429
Of the fixed stars. Their classification by magnitudes. Photometric scale
of magnitudes. Conventional or vulgar scale. Photometric comparison
of stars. Distribution of stars over the heavens. Of the Milky Way or
galaxy. Its supposed form that of a flat stratum partially subdivided.
Its visible course among the constellations. Its internal structure. Its
apparently indefinite extent in certain directions. Of the distance of the
fixed stars. Their annual parallax. Parallactic unit of sidereal distance.
Effect of parallax analogous to that of aberration. How distinguished
from it. Detection of parallax by meridional observations. Henderson's
application to a centauri. By differential observations. Discoveries of
Bessel and Struve. List of stars in which parallax has been detected.
Of the real magnitudes of the stars. Comparison of their lights with that
of the Sun 488
CHAPTER XVI.
Variable and periodical stars. List of those already known. Irregularities
in their periods and lustre when brightest. Irregular and temporary
stars. Ancient Chinese records of several. Missing stars. Double stars.
Their classification. Specimens of each class. Binary systems. Revolu-
tion round each other. Describe elliptic orbits under the Newtonian law
of gravity. Elements of orbits of several. Actual dimensions of their
orbits. Coloured double stars. Phenomenon of complimentary colours.
Sanguine stars. Proper motion of the stars. Partly accounted for by a
real motion of the Sun. Situation of the solar apex. Agreement of
southern and northern stars in giving the same result. Principles on
which the investigation of the solar motion depends. Absolute velocity
of the Sun's motion. Supposed revolution of the whole sidereal system
round a common centre. Systematic parallax and aberration. Effect of
the motion of light in altering the apparent period of a binary star
CHAPTER XVII.
OF CLUSTERS OF STARS AND NEBULE.
Page 520
Of clustering groups of stars. Globular clusters. Their stability dyna-
mically possible. List of the most remarkable. Classification of nebula
and clusters. Their distribution over the heavens. Irregular clusters.
Resolvability of nebula. Theory of the formation of clusters by nebulous
subsidence. Of elliptic nebula. That of Andromeda. Annular and
planetary nebulæ. Double nebula. Nebulous stars. Connection of
nebula with double stars. Insulated nebula of forms not wholly irregular.
Of amorphous nebula. Their law of distribution marks them as outliers
of the galaxy. Nebula and nebulous group of Orion-of Argo-of Sagit-
tarius-of Cygnus. The Magellanic clouds. Singular nebula in the
greater of them. The zodiacal light. Shooting stars
PART IV.
OF THE ACCOUNT OF TIME.
CHAPTER XVIII.
555
Natural Units of time. Relation of the sidereal to the solar day affected
by precession. Incommensurability of the day and year. Its incon-
venience. How obviated. The Julian Calendar. Irregularities at its
first introduction. Reformed by Augustus. Gregorian reformation.
Solar and lunar cycles. Indiction. Julian period. Table of Chrono-
logical eras. Rules for calculating the days elapsed between given Dates.
Equinoctial time.
APPENDIX.
583
I. Lists of Northern and Southern Stars, with their approximate
Magnitudes, on the Vulgar and Photometric Scales
604-5
IV. Elements of Periodical Comets at their last Appearance
II. Synoptic Table of the Elements of the Planetary System
III. Synoptic Table of the Elements of the Orbits of the Satellites, so
far as they are known
606-7
608
.
611
INDEX
612