INTRODUCTION.

CONTENTS.

CHAP. I.

Imaginary Concave Surface. Apparent Motions of Fixed

Stars, Sun, Moon, and Planets. Distance on Concave

Surface measured by Arcs of Circles. Divisions of the

Circle; Horizon; Altitude. Zenith distance. Imaginary

Celestial Poles. Imaginary rotation of the Concave Sur-

face in 23h. 56m. Celestial Equator. Circles of Declin-

ation. Meridian. Reference to Circles of the Sphere by a

Figure. Equable Motion of Rotation of Concave Surface.

Hour Circles. Poles of Horizon, Zenith and Nadir. Ver-

tical Circles. Cardinal Points. Azimuth. Apparent path

of Sun in Ecliptic. Apparent path of Moon in a Month in a

great Circle nearly, intersecting Ecliptic at an Angle of

five degrees. Ecliptic inclined to Equator at an Angle of

23° 28'. Seasons. Tropics. Zodiac and Signs thereof.

Constellations of Zodiac. Apparent advancement of the

constellations of the Zodiac. Position of Object on the

Concave Surface ascertained by Declination and Right As-

cension. Sidereal Time. Portion of Object ascertained by

Longitude and Latitude. Colures

CHAP. II.

Fixed Stars. Proper Names of certain more remarkable Stars.

Number and Names of Stars of first magnitude. Assem-

b

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blages of Stars. Nebulæ. Telescopes. Common Refract-

ing Telescope. Refracting Telescopes. Achromatic Ob-

ject Glasses. Herschel's Telescopes. Appearance of Stars

in Telescopes. Vast number of telescopic Stars. Cata-

logues of Stars. Double Stars. Appearance of new Stars,

and disappearance of others. Changes in Lustre of Stars.

Periodical changes of Lustre. Great number of Nebulæ

discovered by Dr. Herschel

Page.

16

CHAP. III.

Phenomena depending on a Change of Place.

Fixed Stars,

Celestial Pole and Equator appear in the same relative situ-

ation from every part of the Earth. Situation relative to

Horizon Changes with Change of Place. Variation of Alti-

tude of Celestial Pole nearly proportioned to Space gone

over in a direction North or South. Earth nearly a Sphere.

Magnitude of Earth. Axis of Earth. Terestrial Equator.

Latitude and Longitude on Earth. Altitude of Pole equal

to Latitude of Place. Changes of Seasons over the whole

Earth. Oblique Sphere. Right Sphere and Parallel

Spheres. Five Principal Zones. Ancient Zones and

Climates

CHAP. IV.

Refraction from the Effect of the Atmosphere. The apparent

Altitude is always greater than the true. Refraction great-
est in the Horizon; at 45° in its mean quantity = 574".
Quantity of Refraction changed by the Weight and Tem-
perature of the Atmosphere. Change ascertained by the
Heights of the Barometer and Thermometer. Methods of
Observing Quantity of Refraction. Twilight occasioned
by Reflection of Sun's Rays by Atmosphere.-Lasts till the
Sun is 18° below Horizon. Duration of Twilight. Oval

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Page

Figures and apparent Magnitudes of Sun and Moon near

Horizon.

35

CHAP. V.

Micrometers. Method of deducing the Angle subtended by

two. distant places on Earth at Sun, Moon, or Planet.

Apparent Diameter of Earth, as seen from the Sun, Moon,

or Planet. Apparent Diameters of Sun, Moon, or Planet,

as seen from the Earth. Comparison of the real Diameters

of the Earth, Sun, Moon, and Planet. Diurnal Parallax.

Horizontal Parallax. Sun and Planets Spherical Bodies.

Spots of Sun. Sun revolves on an Axis in 25 Days 10

Hours, which Axis is inclined to the Ecliptic at an Angle

of 8240. Rotation of Planets on Axes. Rotation of the

Sun and Planets all the same way from West to East. Mag-

nitude of Sun, Moon, and Planets

40

CHAP. VI.

Rotation of the Earth on an Axis in 23h. 56m. Annual Motion

of the Sun in Ecliptic only apparent, and occasioned by a

real Motion of the Earth about the Sun in an Orbit nearly

circular. The Change of Seasons explained by the Axis,

inclined at an Angle of 66° 32′ to the Plane of the Orbit,

being carried parallel to itself while the Earth moves round

the Sun. No Change in the apparent relative position of

the Fixed Stars in consequence of the Annual Motion of

the Earth; only proves the immense Distance of the Fixed

Stars. Precession of the Equinoxes. The Intersections of

the Equator and Ecliptic appear to move backward on the

Ecliptic, and the visible Pole of the Equator appears to be

moving in a Circle round the Pole of the Ecliptic. These

Motions are nearly uniform at the rate of about 1° in 72

Years. Occasioned by a real Motion in the Earth. Small

variations of the Precession

50

On the Motions of the Primary Planets; Retrograde and

Stationary Appearances. Periodic Times of Inferior and

Superior Planets. Phases of Planets. Table of Planetary

System. Law of Periodic Times. Ptolemaic System . . . 63

CHAP. VIII.

On the Secondary Planets and Moon.

Time of Lunation. Metonic Cycle. Lunar Mountains.

Phases of Moon and

Pole from Zenith. Obliquity of Ecliptic. Right Ascen-

sion .

104

114

CHAP. XI.

Methods of ascertaining minute Portions of Circular Arches.

Astronomical Quadrant. Zenith Sector. Circle. Transit

Instrument. Methods of Finding the Meridian..

CHAP. XII.

Geocentric and Heliocentric places of the Planets. Nodes

and Inclinations of their Orbits.

Mean Motions and

Periodic Times. Discoveries of Kepler. Elliptical Mo-

tions of Planets.

122

142

CHAP. XIII.

On the Motions of the Moon. Satellites. Comets

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157

CHAP. XIV.

Transits of Venus and

. . 168

On Eclipses of the Sun and Moon.

Mercury over the Sun's Disc .

CHAP. XV.

On the Velocity of Light, and Aberration of the Fixed Stars

and Planets. Equation of Time.

Dials

CHAP. XVI.

Application of Astronomy to Navigation. Hadley's Sextant.

Latitude at Sea. Apparent Time. Variation of the Com-

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195