Chapter I: Front Matter

Transcriber’s Note

When italics were used in the original book, the corresponding text has been surrounded by _underscores_ except in the case of single letter variables used in the Notes section, where the italics were not represented. Mixed fractions have been displayed with a hyphen between whole number and fraction for clarity. Superscripted characters are preceded by ^ and when more than one character is superscripted, they are surrounded by {}. This book uses some unusual characters, such as those representing the constellation Aries (♈) and Libra (♎). These characters may fail to display correctly if the font you are using does not support them.

Some corrections have been made to the printed text. These are listed in a second transcriber’s note at the end of the text.

MARY SOMERVILLE
J. COOPER S^c.
]

ON

THE CONNEXION

OF

THE PHYSICAL SCIENCES.

BY MARY SOMERVILLE,

AUTHORESS OF ‘MECHANISM OF THE HEAVENS,’ AND
‘PHYSICAL GEOGRAPHY.’

---------------------

“No natural phenomenon can be adequately studied in itself alone—but, to be understood, it must be considered as it stands connected with all Nature.”—BACON.

---------------------

Ninth Edition, completely Revised.

LONDON:
JOHN MURRAY, ALBEMARLE STREET.
1858.

_The right of Translation is reserved._

LONDON: PRINTED BY W. CLOWES AND SONS, DUKE STREET, STAMFORD STREET,
AND CHARING CROSS.

This Book is Dedicated

TO

HER DEAR CHILDREN,

BY THEIR AFFECTIONATE MOTHER,

MARY SOMERVILLE.

_Florence, Nov. 1, 1858._

CONTENTS.

INTRODUCTION

Page 1

SECTION I.

Attraction of a Sphere—Form of Celestial Bodies—Terrestrial Gravitation
retains the Moon in her Orbit—The Heavenly Bodies move in Conic
Sections—Gravitation Proportional to Mass—Gravitation of the Particles
of Matter—Figure of the Planets—How it affects the Motions of their
Satellites—Rotation and Translation impressed by the same
Impulse—Motion of the Sun and Solar System

4

SECTION II.

Elliptical Motion—Mean and True
Motion—Equinoctial—Ecliptic—Equinoxes—Mean and True Longitude—Equation
of Centre—Inclination of the Orbits of Planets—Celestial
Latitude—Nodes—Elements of an Orbit—Undisturbed or Elliptical
Orbits—Great Inclination of the Orbits of the New Planets—Universal
Gravitation the Cause of Perturbations in the Motions of the Heavenly
Bodies—Problem of the Three Bodies—Stability of Solar System depends
upon the Primitive Momentum of the Bodies

8

SECTION III.

Perturbations, Periodic and Secular—Disturbing Action equivalent to
three Partial Forces—Tangential Force the cause of the Periodic
Inequalities in Longitude, and Secular Inequalities in the Form and
Position of the Orbit in its own Plane—Radial Force the cause of
Variations in the Planet’s Distance from the Sun—It combines with the
Tangential Force to produce the Secular Variations in the Form and
Position of the Orbit in its own Plane—Perpendicular Force the cause
of Periodic Perturbations in Latitude, and Secular Variations in the
Position of the Orbit with regard to the Plane of the Ecliptic—Mean
Motion and Major Axis Invariable—Stability of System—Effects of a
Resisting Medium—Invariable Plane of the Solar System and of the
Universe—Great Inequality of Jupiter and Saturn

13

SECTION IV.

Theory of Jupiter’s Satellites—Effects of the Figure of Jupiter upon his
Satellites—Position of their Orbits—Singular Laws among the Motions of
the first Three Satellites—Eclipses of the Satellites—Velocity of
Light—Aberration—Ethereal Medium—Satellites of Saturn and Uranus

27

SECTION V.

Lunar Theory—Periodic Perturbations of the Moon—Equation of
Centre—Evection—Variation—Annual Equation—Direct and Indirect
Action of Planets—The Moon’s Action on the Earth disturbs her
own Motion—Excentricity and Inclination of Lunar Orbit
invariable—Acceleration—Secular Variation in Nodes and
Perigee—Motion of Nodes and Perigee inseparably connected with
the Acceleration—Nutation of Lunar Orbit—Form and Internal
Structure of the Earth determined from it—Lunar, Solar, and
Planetary Eclipses—Occultations and Lunar Distances—Mean
Distance of the Sun from the Earth obtained from Lunar
Theory—Absolute Distances of the Planets, how found

34

SECTION VI.

Form of the Earth and Planets—Figure of a Homogeneous Spheroid in
Rotation—Figure of a Spheroid of variable Density—Figure of the Earth,
supposing it to be an Ellipsoid of Revolution—Mensuration of a Degree
of the Meridian—Compression and Size of the Earth from Degrees of
Meridian—Figure of Earth from the Pendulum

44

SECTION VII.

Parallax—Lunar Parallax found from Direct Observation—Solar Parallax
deduced from the Transit of Venus—Distance of the Sun from the
Earth—Annual Parallax—Distance of the Fixed Stars

52

SECTION VIII.

Masses of Planets that have no Satellites determined from their
Perturbations—Masses of the others obtained from the Motions of their
Satellites—Masses of the Sun, the Earth, of Jupiter and of the Jovial
System—Mass of the Moon—Real Diameters of Planets, how obtained—Size
of Sun, Densities of the Heavenly Bodies—Formation of Astronomical
Tables—Requisite Data and Means of obtaining them

55

SECTION IX.

Rotation of the Sun and Planets—Saturn’s Rings—Periods of the Rotation
of the Moon and other Satellites equal to the Periods of their
Revolutions—Form of Lunar Spheroid—Libration, Aspect, and Constitution
of the Moon—Rotation of Jupiter’s Satellites

65

SECTION X.

Rotation of the Earth invariable—Decrease in the Earth’s mean
Temperature—Earth originally in a state of Fusion—Length of Day
constant—Decrease of Temperature ascribed by Sir John Herschel to the
variation in the Excentricity of the Terrestrial Orbit—Difference in
the Temperature of the two Hemispheres erroneously ascribed to the
Excess in the Length of Spring and Summer in the Southern Hemisphere;
attributed by Sir Charles Lyell to the Operation of existing
Causes—Three principal Axes of Rotation—Position of the Axis of
Rotation on the Surface of the Earth invariable—Ocean not sufficient
to restore the Equilibrium of the Earth if deranged—Its Density and
mean Depth—Internal Structure of the Earth

71

SECTION XI.

Precession and Nutation—Their Effects on the Apparent Places of the
Fixed Stars

79

SECTION XII.

Mean and Apparent Sidereal Time—Mean and Apparent Solar Time—Equation of
Time—English and French Subdivisions of Time—Leap Year—Christian
Era—Equinoctial Time—Remarkable Eras depending upon the Position of
the Solar Perigee—Inequality of the Lengths of the Seasons in the two
Hemispheres—Application of Astronomy to Chronology—English and French
Standards of Weights and Measures

83

SECTION XIII.

Tides—Forces that produce them—Origin and Course of Tidal Wave—Its
Speed—Three kinds of Oscillations in the Ocean—The Semidiurnal
Tides—Equinoctial Tides—Effects of the Declination of the Sun and
Moon—Theory insufficient without Observation—Direction of the Tidal
Wave—Height of Tides—Mass of Moon obtained from her Action on the
Tides—Interference of Undulations—Impossibility of a Universal
Inundation—Currents

91

SECTION XIV.

Molecular Forces—Permanency of the ultimate Particles of
Matter—Interstices—Mossotti’s Theory—Rankin’s Theory of Molecular
Vortices—Gases reduced to Liquids by Pressure—Gravitation of
Particles—Cohesion—Crystallization—Cleavage—Isomorphism—Minuteness of
the Particles—Height of Atmosphere—Chemical Affinity—Definite
Proportions and Relative Weights of Atoms—Faraday’s Discovery with
regard to Affinity—Capillary Attraction

102

SECTION XV.

Analysis of the Atmosphere—Its pressure—Law of Decrease in
Density—Law of Decrease in Temperature—Measurement of Heights
by the Barometer—Extent of the Atmosphere—Barometrical
Variations—Oscillations—Trade-Winds—Cloud-Ring—Monsoons—Rotation of
Winds—Laws of Hurricanes

117

SECTION XVI.

Sound—Propagation of Sound illustrated by a Field of Standing
Corn—Nature of Waves—Propagation of Sound through the
Atmosphere—Intensity—Noises—A Musical Sound—Quality—Pitch—Extent of
Human Hearing—Velocity of Sound in Air, Water, and Solids—Causes of
the Obstruction of Sound—Law of its Intensity—Reflection of
Sound—Echoes—Thunder—Refraction of Sound—Interference of Sounds

129

SECTION XVII.

Vibration of Musical Strings—Harmonic Sounds—Nodes—Vibration of Air in
Wind-Instruments—Vibration of Solids—Vibrating
Plates—Bells—Harmony—Sounding Boards—Forced
Vibrations—Resonance—Speaking Machines

140

SECTION XVIII.

Refraction—Astronomical Refraction and its Laws—Formation of Tables of
Refraction—Terrestrial Refraction—Its Quantity—Instances of
Extraordinary Refraction—Reflection—Instances of Extraordinary
Reflection—Loss of Light by the Absorbing Power of the
Atmosphere—Apparent Magnitude of Sun and Moon in the Horizon

153

SECTION XIX.

Constitution of Light according to Sir Isaac Newton—Absorption of
Light—Colours of Bodies—Constitution of Light according to Sir David
Brewster—New Colours—Fraunhofer’s Dark Lines—Dispersion of Light—The
Achromatic Telescope—Homogeneous Light—Accidental and Complementary
Colours—M. Plateau’s Experiments and Theory of Accidental Colours

159

SECTION XX.

Interference of Light—Undulatory Theory of Light—Propagation of
Light—Newton’s Rings—Measurement of the Length of the Waves of Light,
and of the Frequency of the Vibrations of Ether for each
Colour—Newton’s Scale of Colours—Diffraction of Light—Sir John
Herschel’s Theory of the Absorption of Light—Refraction and Reflection
of Light

167

SECTION XXI.

Polarization of Light—Defined—Polarization by Refraction—Properties of
the Tourmaline—Double Refraction—All doubly Refracted Light is
Polarized—Properties of Iceland Spar—Tourmaline absorbs one of the two
Refracted Rays—Undulations of Natural Light—Undulations of Polarized
Light—The Optic Axes of Crystals—M. Fresnel’s Discoveries on the Rays
passing along the Optic Axis—Polarization by Reflection

179

SECTION XXII.

Phenomena exhibited by the Passage of Polarized Light through Mica and
Sulphate of Lime—The Coloured Images produced by Polarized Light
passing through Crystals having one and two Optic Axes—Circular
Polarization—Elliptical Polarization—Discoveries of MM. Biot, Fresnel,
and Professor Airy—Coloured Images produced by the Interference of
Polarized Rays—Fluorescence

186

SECTION XXIII.

Objections to the Undulatory Theory, from a difference in the Action of
Sound and Light under the same circumstances, removed—The Dispersion
of Light according to the Undulatory Theory—Arago’s final proof that
the Undulatory Theory is the Law of Nature

199

SECTION XXIV.

Chemical or Photographic Rays of Solar Spectrum—Scheele, Ritter, and
Wollaston’s Discoveries—Wedgwood’s and Sir Humphry Davy’s Photographic
Pictures—The Calotype—The Daguerreotype—The Chromatype—The
Cyanotype—Collodion—Sir John Herschel’s Discoveries in the Chemical
Spectrum—M. Becquerel’s Discoveries of Inactive Lines in ditto—Thermic
Spectrum—Phosphoric Spectrum—Electrical Properties—Parathermic
Rays—Moser and Hunt’s Experiments—General Structure and antagonist
Properties of Solar Spectrum—Defracted Spectrum

203

SECTION XXV.

Size and Constitution of the Sun—The Solar Spots—Intensity of the
Sun’s Light and Heat—The Sun’s Atmosphere—His influence on the
Planets—Atmospheres of the Planets—The Moon has none—Lunar
heat—The Differential Telescope—Temperature of Space—Internal
Heat of the Earth—Zone of constant Temperature—Increase of Heat
with the Depth—Central Heat—Volcanic Action—Quantity of Heat
received from the Sun—Isogeothermal Lines—Line of Perpetual
Congelation—Climate—Isothermal Lines—Same quantity of Heat
annually received and radiated by the Earth

224

SECTION XXVI.

Influence of Temperature on Vegetation—Vegetation varies with the
Latitude and Height above the Sea—Geographical Distribution of Land
Plants—Distribution of Marine Plants—Corallines, Shell-fish, Reptiles,
Insects, Birds, and Quadrupeds—Varieties of Mankind, yet identity of
Species

248

SECTION XXVII.

Terrestrial Heat—Radiation—Transmission—Melloni’s experiments—Heat
in Solar Spectrum—Polarization of Heat—Nature of
Heat—Absorptions—Dew—Rain—Combustion—Expansion—Compensation
Pendulum—Transmission through Crystals—Propagation—Dynamic Theory
of Heat—Mechanical equivalent of Heat—Latent Heat is the Force of
Expansion—Steam—Work performed by Heat—Conservation of
Force—Mechanical Power in the Tides—Dynamical Power of
Light—Analogy between Light, Heat, and Sound

257

SECTION XXVIII.

Common or Static Electricity, or Electricity of Tension—A Dual
Power—Methods of exciting it—Attraction and
Repulsion—Conduction—Electrics and
Non-electrics—Induction—Dielectrics—Tension—Law of the Electric
Force—Distribution—Laws of Distribution—Heat of Electricity—Electrical
Light and its Spectrum—Velocity—Atmospheric Electricity—Its
cause—Electric Clouds—Violent effects of Lightning—Back
Stroke—Electric Glow—Phosphorescence

282

SECTION XXIX.

Voltaic Electricity—The Voltaic Battery—Intensity—Quantity—Static
Electricity, and Electricity in Motion—Luminous Effects—Mr.
Grove on the Electric Arc and Light—Decomposition of Water—Formation
of Crystals by Voltaic Electricity—Photo-galvanic
Engraving—Conduction—Heat of Voltaic Electricity—Electric Fish

297

SECTION XXX.

Discovery of Electro-magnetism—Deflection of the Magnetic Needle by a
Current of Electricity—Direction of the Force—Rotatory Motion by
Electricity—Rotation of a Wire and a Magnet—Rotation of a Magnet about
its Axis—Of Mercury and Water—Electro-Magnetic Cylinder or
Helix—Suspension of a Needle in a Helix—Electro-Magnetic
Induction—Temporary Magnets—The Galvanometer

312

SECTION XXXI.

Electro-Dynamics—Reciprocal Action of Electric Currents—Identity of
Electro-Dynamic Cylinders and Magnets—Differences between the Action
of Voltaic Electricity and Electricity of Tension—Effects of a Voltaic
Current—Ampère’s Theory—Dr. Faraday’s Experiment of Electrifying and
Magnetising a Ray of Light

316

SECTION XXXII.

Magneto-Electricity—Volta-Electric Induction—Magneto-Electric
Induction—Identity in the Action of Electricity and
Magnetism—Description of a Magneto-Electric Apparatus and its
Effects—Identity of Magnetism and Electricity—The Submarine Telegraph

322

SECTION XXXIII.

Electricity produced by Rotation—Direction of the Currents—Electricity
from the Rotation of a Magnet—M. Arago’s Experiment explained—Rotation
of a Plate of Iron between the Poles of a Magnet—Relation of
Substances to Magnets of three Kinds—Thermo-Electricity

330