Saturn and Its System

ib.

Determines Period of Rotation of Outer Ring

Measures the Planet and Rings

Examines the Rings when their Edge is turned to the Earth

Relative Dimensions of the various Members of the Solar System, and of their

Orbits

Telescopic Powers necessary to observe the various Phenomena presented by

Saturn's System

75

CHAPTER IV.

THE PERIODIC CHANGES IN THE APPEARANCE OF SATURN'S SYSTEM.

Direction of Saturn's Axis unchanged during his Revolution about the Sun

Position of the Ring's Plane with respect to the Ecliptic and to Saturn's Orbit

Changes of Appearance that would be presented to an observer supposed to be

placed at the Sun's centre during a complete Revolution of Saturn

Effect of the Inclination of Saturn's Orbit to the Ecliptie.

Disappearances and Reappearances of the Ring explained.

The Shadow of the Rings on the Planet, and of the Planet on the Rings

Construction of a Saturnian Orrery

Changes in the Figures of the Saturnian Belts explained

Saturn never Gibbous

Eclipses, Occultations, and Transits of Saturn's Satellites.

CHAPTER V.

NATURE OF THE RINGS.

Speculations of Maupertius, Buffon, and Mairan

Objections to the Solidity of Saturn's Rings, drawn from--

Suggests that they may be non-uniform Solids eccentrically placed

114

Pierce and Maxwell prove that the Rings cannot be Solid .

116

Nor Fluid

ib.

Instances of Rings of disconnected Bodies in the Universe

Difficulties before considered disappear on the Hypothesis that Saturn's Rings

Appearances observed by Wray and O. Struve explained

Problem of the Motions of Rings of Satellites too complex for exact Solution

Such Rings safe from sudden Destruction

123

Extra-planar Disturbances and their Effects

ib.

Waves of Concentration and Dispersion, and their Effects.

124

Collisions among the Satellites and their Effects

125

Observed Changes in the Rings correspond with the Results of Analysis

126

CHAPTER VI.

6
THE GREAT INEQUALITY' OF SATURN AND JUPITER.

Irregularities in the Motions of Saturn and Jupiter

Variable Elements of the Planetary Orbits

Effects of Normal Disturbing Forces

Effects of Perpendicular Disturbing Forces

Effects of Tangential Disturbing Forces

These Forces generally combine their Effects

Examination of the Motions of an inferior disturbed by a superior Planet-

(i) Orbits of both Planets circular

(ii) Orbit of inferior Planet (alone) Elliptic

(iii) Orbit of superior Planet (alone) Elliptic

(iv) Orbits of both Planets Elliptic

PAGE

Results are directly applicable to the case of a superior disturbed by an inferior

Planet

Approach to a Simple Relation of Commensurability between the Periods of

Saturn and Jupiter

More exact Examination of the Motions of the two Planets

Disturbing Effects due to-

The Forms and Positions of the two Orbits

The varying Intervals between successive Conjunctions

The variable Distance between the two Planets at successive Conjunctions

The variable Motions of the two Planets

The varying Intervals between successive Triple Conjunctions

The varying Periods of the two Planets

The Inclination of the Planes of their Orbits

The Variations in the Radial and Perpendicular Forces .

Results of the Analytical Examination of these Disturbances

Cycle of Disturbances

Disturbances caused by the other Members of the Solar System

Variations in the Eccentricity and Inclination of Saturn's Orbit

Lagrange's Laws

ib.

ib.

Density of Materials composing Saturn's Globe not necessarily the same as the

mean Density of the Globe

158

Oceans on Saturn's Surface not necessarily collected in one Hemisphere

Parts of Saturn's Surface from which the different Rings are visible

Apparent Outlines of the Rings viewed from different parts of Saturn's Surface.

171

Rings not always Visible, and variable in Brilliancy

.

176

Motion of the Shadow of the Planet across the Rings—how Variable

Seven Inner Satellites cannot be eclipsed by the Rings, except for places near

Saturn's Equater

ib.

Satellites vary in apparent Magnitude as they traverse the Saturnian Sky

ib.

Jupiter and Uranus, only Planets visible from Saturn

NOTE A.-CHALDEAN ASTRONOMY.

Eastern Systems of Astronomy not derived from the Egyptians, Chinese, Indians,

Chaldæans not originally settled in Mesopotamia

Bailly's Objections to the Chaldæan Origin of Astronomy considered

Fabulous Accounts of Chaldæan Astronomical System

Real Discoveries effected by the Chaldæans

Chaldæans probably acquainted with True System of the Universe

Opinions attributed by Philolaus to Pythagoras-how probably derived

Chaldæans not acquainted with Gravity

Mechanical Skill of the Assyrians

Astronomical Observations-how recorded by the Chaldæans

Assyrians acquainted with the Laws of Optics .

Mythological System of the Assyrians

Mylitta and Bel-how represented

Attributes of Nisroch, the Time-God

Nisroch represented within a Ring

Figure of a Ring commonly met with in engraved Tablets.

ib.

These may be ascribed to a Law of Development, since 'God works nothing in

How the Theory must be modified to correspond with modern Scientific Discoveries ib.

Motions of the Satellites of Uranus and Neptune-how reconcilable with Laplace's

Theory

203

Laplace Theory reconcilable with the Scripture Account of Creation.

Changes going on in Saturn's Ring-System correspond with the Processes con-

ceived by Laplace

NOTE C.-HABITABILITY OF THE MOON.

204

.

206

Physical Condition of the Moon very different from that of the Earth

Arguments against the Existence of a Lunar Atmosphere.

Attempt to reconcile these Arguments by Considerations drawn from the Moon's

Figure

209

Improbable that all Traces of a Lunar Atmosphere should be concealed in the

manner suggested

210

Colour of the Moon not such as the Earth would present at the Moon's distance 211

Effects of Diminution of Temperature

ib.

Oceans on the Moon's Surface probably Frozen, and Gases once enveloping the

Moon condensed to the Liquid or Solid Forms

ib.

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220

VII.-For Determining the Appearance of Saturn's Rings, &c.

VIII.-For Calculating the Elevation of the Sun above the Plane of the Rings, &c. 221

IX. Great Inequality of Saturn and Jupiter.

X.-Passages of the Ring's Plane through the Sun between the years 1600

and 2000

XI.-For Determining the Sun's Diurnal Path on the Saturnian Heavens at

the Saturnian Solstices and Equinoxes, the Appearance of the Rings,

and the Eclipses of the Sun by the Rings, for different Latitudes

on Saturn's Globe

Explanation of the Tables

Explanation of Astronomical Terms

224

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Saturn and Its System: Containing Discussions of the Motions (real and ...