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General notions. Apparent and real motions. Shape and size of the
Earth. The horizon and its dip. The atmosphere. Refraction. Twi-
light. 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 phænomena to the Earth's centre as a common
conventional station
CHAPTER II.
11
Terminology and elementary geometrical conceptions and relations. Ter-
minology relating to the globe of the Earth-to the celestial sphere.
Celestial perspective
CHAPTER III.
58
Of the nature of astronomical instruments and observations in general.
Of sidereal and solar time. Of the measurements of time. Clocks,
chronometers. Of astronomical measurements. Principle of telescopic
sights to increase the accuracy of pointing. Simplest application of
this principle. 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 Bohnenberger. Of compound instruments with
co-ordinate circles. The equatorial, altitude, and azimuth instrument.
Theodolite. Of the sextant and reflecting circle. Principle of re-
petition. Of micrometers. Parallel wire micrometer. Principle of the
duplication of images. The heliometer. Double refracting eye-piece.
Variable prism micrometer. Of the position micrometer. Illumination
of wires. Solar telescope and eye-piece. Helioscopy. Collimation of
large reflectors
75
CHAPTER IV.
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 pendulum.
Gravity to a spheroid. Other effects of the Earth's rotation. Trade
winds. Veering of the winds. Cyclones. Foucault's pendulum. The
gyroscope. Determination of geographical positions—of latitudes-of
longitudes. Conduct of a trigonometrical survey. Of maps.
jections of the sphere. Measurement of heights by the barometer.
CHAPTER V.
OF URANOGRAFHY.
Pro-
Page 129
Construction of celestial maps and globes by observations of right ascen-
sion 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.
Refraction. Parallax. Summary view of the uranographical cor-
rections
CHAPTER VI.
OF THE SUN'S MOTION AND PHYSICAL CONSTITUTION.
- 190
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. Effect of excentricity of the orbit and
position of its axis on climate. Mean and true longitudes of the Sun.
Equation of the center. Sidereal, tropical, and anomalistic years.
Physical constitution of the Sun. Its spots. Facula. Probable
nature and cause of the spots. Recent discoveries of Mr. Dawes.
Of Mr. Nasmyth. Rotation of the Sun on its axis. Its atmosphere.
Supposed clouds. Periodical recurrence of a more and less spotted
state of its surface. Temperature of its surface. Its expenditure of
heat. Probable cause of solar radiation
CHAPTER VII.
219
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. Harvest Moon. Of
eclipses more particularly. Their phænomena. Their periodical recur-
rence. Physical constitution of the Moon. Its mountains and other
superficial features. Indications of former volcanic activity. Its atmo-
sphere. Climate. Radiation of heat from its surface. Rotation on
its own axis. Libration. Appearance of the Earth from it. Probable
elongation of the Moon's figure in the direction of the Earth. Its
habitability not impossible. Charts, models, and photographs of its
Page 202
surface
CHAPTER VIII.
-
Of terrestrial gravity. Of the law of universal gravitation. Paths of
projectiles, 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. Disturbing effect of the Sun on the Moon's motion 290
CHAPTER IX.
OF THE SOLAR SYSTEM.
Apparent motions of the planets. The stations and retrogradations.
The Sun their natural center 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 heliocentric and geocentric place. Empirical law of planetary
distances; violated in the case of Neptune. The asteroids. Physical
peculiarities observable in each of the planets 301
CHAPTER X.
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 Jupiter's
satellites. Their eclipses, etc. Velocity of light discovered by their
Satellites of Saturn-of Uranus-of Neptune - 354
means.
CHAPTER XI.
OF COMETS.
Great number of recorded comets. The number of those unrecorded
probably much greater. General description of a comet. Comets with-
out tails, or with more than one. Their extreme tenuity. Their
probable structure. Motions conformable to the law of gravity.
Actual dimensions of comets. Periodical return of several. Halley's
Other ancient comets probably periodic. Encke's comet-
comet.
Biela's - Faye's - Lexell's - De Vico's-Brorsen's - Peter's. Great
comet of 1843. Its probable identity with several older comets. Great
interest at present attached to cometary astronomy, and its reasons.
Remarks on cometary orbits in general. Great comet of 1858
PART II.
OF THE LUNAR AND PLANETARY PERTURBATIONS.
Page 370
CHAPTER XII.
Subject propounded. Problem of three bodies. Superposition of small
motions. Estimation of the disturbing force. Its geometrical repre-
sentation. Numerical estimation in particular cases. Resolution into
rectangular components. Radial, transversal, and orthogonal dis-
turbing 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 reverse case. In every case the node of the dis-
turbed 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 diminu-
tion. Average effect in a whole revolution. Compensation in a com-
plete revolution of the nodes. Lagrange's theorem of the stability of
the inclinations of the planetary orbits. Change of obliquity of the
ecliptic. Precession of the equinoxes explained. Nutation. Prin-
ciple of forced vibrations
410
CHAPTER XIII.
THEORY OF THE AXES, PERIHELIA, AND EXCENTRICITIES.
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. Geometri-
cal 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. Ex-
perimental illustration. Application 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
CHAPTER XIV.
- 445
Of the inequalities independent of the excentricities. The Moon's va-
riation and parallactic inequality. Analogous planetary inequalities.
Three cases of Planetary perturbation distinguished. Of inequalities
dependent on the excentricites. 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 ine-
qualities. Annual equation of the Moon. Her secular acceleration.
Lunar inequalities due to the action of Venus. Effect of the sphe-
roidal figure of the Earth and other planets on the motions of their
satellites. Of the tides. Masses of disturbing bodies deducible from
the perturbations they produce. Mass of the Moon, and of Jupiter's
satellites, how ascertained. Perturbations of Uranus resulting in the
discovery of Neptune. Determination of the absolute mass and den-
sity of the Earth
Of the fixed stars.
PART III.
OF SIDEREAL ASTRONOMY.
CHAPTER XV.
Page 486
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 direc-
tions. 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 paral-
lax by meridional observations. Henderson's application to a cen-
tauri. By differential observations. Discoveries of Bessel and Struve.
List of stars in which parallax has been detected. Of the real magni-
tudes of the stars. Comparison of their lights with that of the Sun -
561
CHAPTER XVI.
Specimens of each class. Binary
other. Describe elliptic orbits
Elements of orbits of several.
Coloured double stars. Phæno-
Variable and periodical stars. List of those already known. Irre-
gularities in their periods and lustre when brightest. Irregular and
temporary stars. Ancient Chinese records of several. Missing stars.
Double stars. Their classification.
systems. Revolution round each
under the Newtonian law of gravity.
Actual dimensions of their orbits.
menon of complementary colours. Sanguine stars. Proper motion of
the stars. Partly accounted for by a real motion of the Sun. Situa-
tion of the solar apex. Agreement of southern and northern stars