Chapter II: Preface: To the First Edition

The progress of astronomy during the last hundred years has been rapid and extraordinary. In its distinctive features, moreover, the nature of that progress has been such as to lend itself with facility to untechnical treatment. To this circumstance the present volume owes its origin. It embodies an attempt to enable the ordinary reader to follow, with intelligent interest, the course of modern astronomical inquiries, and to realize (so far as it can at present be realized) the full effect of the comprehensive change in the whole aspect, purposes, and methods of celestial science introduced by the momentous discovery of spectrum analysis.

Since Professor Grant's invaluable work on the _History of Physical Astronomy_ was published, a third of a century has elapsed. During the interval a so-called "new astronomy" has grown up by the side of the old. One effect of its advent has been to render the science of the heavenly bodies more popular, both in its needs and in its nature, than formerly. More popular in its needs, since its progress now primarily depends upon the interest in, and consequent efforts towards its advancement of the general public; more popular in its nature, because the kind of knowledge it now chiefly tends to accumulate is more easily intelligible--less remote from ordinary experience--than that evolved by the aid of the calculus from materials collected by the use of the transit-instrument and chronograph.

It has thus become practicable to describe in simple language the most essential parts of recent astronomical discoveries, and, being practicable, it could not be otherwise than desirable to do so. The service to astronomy itself would be not inconsiderable of enlisting wider sympathies on its behalf, while to help one single mind towards a fuller understanding of the manifold works which have in all ages irresistibly spoken to man of the glory of God might well be an object of no ignoble ambition.

The present volume does not profess to be a complete or exhaustive history of astronomy during the period covered by it. Its design is to present a view of the progress of celestial science, on its most characteristic side, since the time of Herschel. Abstruse mathematical theories, unless in some of their more striking results, are excluded from consideration. These, during the eighteenth century, constituted the sum and substance of astronomy, and their fundamental importance can never be diminished, and should never be ignored. But as the outcome of the enormous development given to the powers of the telescope in recent times, together with the swift advance of physical science, and the inclusion, by means of the spectroscope, of the heavenly bodies within the domain of its inquiries, much knowledge has been acquired regarding the nature and condition of those bodies, forming, it might be said, a science apart, and disembarrassed from immediate dependence upon intricate, and, except to the initiated, unintelligible formulæ. This kind of knowledge forms the main subject of the book now offered to the public.

There are many reasons for preferring a history to a formal treatise on astronomy. In a treatise, _what_ we know is set forth. A history tells us, in addition, _how_ we came to know it. It thus places facts before us in the natural order of their ascertainment, and narrates instead of enumerating. The story to be told leaves the marvels of imagination far behind, and requires no embellishment from literary art or high-flown phrases. Its best ornament is unvarnished truthfulness, and this, at least, may confidently be claimed to be bestowed upon it in the ensuing pages.

In them unity of treatment is sought to be combined with a due regard to chronological sequence by grouping in separate chapters the various events relating to the several departments of descriptive astronomy. The whole is divided into two parts, the line between which is roughly drawn at the middle of the present century. Herschel's inquiries into the construction of the heavens strike the keynote of the first part; the discoveries of sun-spot and magnetic periodicity and of spectrum analysis determine the character of the second. Where the nature of the subject required it, however, this arrangement has been disregarded. Clearness and consistency should obviously take precedence of method. Thus, in treating of the telescopic scrutiny of the various planets, the whole of the related facts have been collected into an uninterrupted narrative. A division elsewhere natural and helpful would here have been purely artificial, and therefore confusing.

The interests of students have been consulted by a full and authentic system of references to the sources of information relied upon. Materials have been derived, as a rule with very few exceptions, from the original authorities. The system adopted has been to take as little as possible at second-hand. Much pains have been taken to trace the origin of ideas, often obscurely enunciated long before they came to resound through the scientific world, and to give to each individual discoverer, strictly and impartially, his due. Prominence has also been assigned to the biographical element, as underlying and determining the whole course of human endeavour. The advance of knowledge may be called a vital process. The lives of men are absorbed into and assimilated by it. Inquiries into the kind and mode of the surrender in each separate case must always possess a strong interest, whether for study or for example.

The acknowledgments of the writer are due to Professor Edward S. Holden, director of the Washburn Observatory, Wisconsin, and to Dr. Copeland, chief astronomer of Lord Crawford's Observatory at Dunecht, for many valuable communications.

London, _September_, 1885.

CONTENTS

_INTRODUCTION_

page
Three Kinds of Astronomy--Progress of the Science during the
Eighteenth Century--Popularity and Rapid Advance during the Nineteenth
Century 1

PART I

_PROGRESS OF ASTRONOMY DURING THE FIRST HALF OF THE NINETEENTH CENTURY_

CHAPTER I

FOUNDATION OF SIDEREAL ASTRONOMY

State of Knowledge regarding the Stars in the Eighteenth Century--
Career of Sir William Herschel--Constitution of the Stellar System--
Double Stars--Herschel's Discovery of their Revolutions--
His Method of Star-gauging--Discoveries of Nebulæ--Theory of their
Condensation into Stars--Summary of Results 9

CHAPTER II

PROGRESS OF SIDEREAL ASTRONOMY

Exact Astronomy in Germany--Career of Bessel--His _Fundamenta
Astronomiæ_--Career of Fraunhofer--Parallaxes of Fixed
Stars--Translation of the Solar System--Astronomy of the
Invisible--Struve's Researches in Double Stars--Sir John Herschel's
Exploration of the Heavens--Fifty Years' Progress 27

CHAPTER III

PROGRESS OF KNOWLEDGE REGARDING THE SUN

Early Views as to the Nature of Sun-spots--Wilson's Observations and
Reasonings--Sir William Herschel's Theory of the Solar
Constitution--Sir John Herschel's Trade-Wind Hypothesis--Baily's
Beads--Total Solar Eclipse of 1842--Corona and Prominences--Eclipse of
1851 52

CHAPTER IV

PLANETARY DISCOVERIES

Bode's Law--Search for a Missing Planet--Its Discovery by Piazzi-- Further Discoveries of Minor Planets--Unexplained Disturbance of Uranus--Discovery of Neptune--Its Satellite--An Eighth Saturnian Moon--Saturn's Dusky Ring--The Uranian System 71

CHAPTER V

COMETS

Predicted Return of Halley's Comet--Career of Olbers--Acceleration of
Encke's Comet--Biela's Comet--Its Duplication--Faye's Comet--Comet of
1811--Electrical Theory of Cometary Emanations--The Earth in a Comet's
Tail--Second Return of Halley's Comet--Great Comet of 1843--Results to
Knowledge 88

CHAPTER VI

INSTRUMENTAL ADVANCES

Two Principles of Telescopic Construction--Early Reflectors--Three
Varieties--Herschel's Specula--High Magnifying Powers--Invention of
the Achromatic Lens--Guinand's Optical Glass--The Great Rosse
Reflector--Its Disclosures--Mounting of Telescopes--Astronomical
Circles--Personal Equation 108

PART II

_RECENT PROGRESS OF ASTRONOMY_

CHAPTER I

FOUNDATION OF ASTRONOMICAL PHYSICS

Schwabe's Discovery of a Decennial Sun-spot Period--Coincidence with
Period of Magnetic Disturbance--Sun-spots and Weather--Spectrum
Analysis--Preliminary Inquiries--Fraunhofer Lines--Kirchhoff's
Principle--Anticipations--Elementary Principles of Spectrum
Analysis--Unity of Nature 125

CHAPTER II

SOLAR OBSERVATIONS AND THEORIES

Black Openings in Spots--Carrington's Observations--Rotation of the
Sun--Kirchhoff's Theory of the Solar Constitution--Faye's Views--Solar
Photography--Kew Observations--Spectroscopic Method--Cyclonic Theory
of Sun-spots--Volcanic Hypothesis--A Solar Outburst--Sun-spot
Periodicity--Planetary Influence--Structure of the Photosphere 143

CHAPTER III

RECENT SOLAR ECLIPSES

Expeditions to Spain--Great Indian Eclipse--New Method of Viewing
Prominences--Total Eclipse Visible in North America--Spectrum of the
Corona--Eclipse of 1870--Young's Reversing Layer--Eclipse of
1871--Corona of 1878--Varying Coronal Types--Egyptian
Eclipse--Daylight Coronal Photography--Observations at Caroline
Island--Photographs of Corona in 1886 and 1889--Eclipses of 1896,
1898, 1900, and 1901--Mechanical Theory of Corona--Electro-Magnetic
Theories--Nature of Corona 166

CHAPTER IV

SOLAR SPECTROSCOPY

Chemistry of Prominences--Study of their Forms--Two
Classes--Photographs and Spectrographs of Prominences--Their
Distribution--Structure of the Chromosphere--Spectroscopic Measurement
of Radial Movements--Spectroscopic Determination of Solar
Rotation--Velocities of Transport in the Sun--Lockyer's Theory of
Dissociation--Solar Constituents--Oxygen Absorption in Solar
Spectrum 194

CHAPTER V

TEMPERATURE OF THE SUN

Thermal Power of the Sun--Radiation and Temperature--Estimates of
Solar Temperature--Rosetti's and Wilson's Results--Zöllner's Method
--Langley's Experiment at Pittsburg--The Sun's Atmosphere--Langley's
Bolometric Researches--Selective Absorption by our Air--The Solar
Constant 216

CHAPTER VI

THE SUN'S DISTANCE

Difficulty of the Problem--Oppositions of Mars--Transits of
Venus--Lunar Disturbance--Velocity of Light--Transit of
1874--Inconclusive Result--Opposition of Mars in 1877--Measurements of
Minor Planets--Transit of 1882--Newcomb's Determination of the
Velocity of Light--Combined Result 227

CHAPTER VII

PLANETS AND SATELLITES

Schröter's Life and Work--Luminous Appearances during Transits of
Mercury--Mountains of Mercury--Intra-Mercurian Planets--Schiaparelli's
Results for the Rotation of Mercury and Venus--Illusory
Satellite--Mountains and Atmosphere of Venus--Ashen Light--Solidity of
the Earth--Variation of Latitude--Secular Changes of Climate--Figure
of the Globe--Study of the Moon's Surface--Lunar Atmosphere--New
Craters--Thermal Energy of Moonlight--Tidal Friction 243

CHAPTER VIII

PLANETS AND SATELLITES--(_continued_)

Analogy between Mars and the Earth--Martian Snowcaps, Seas, and
Continents--Climate and Atmosphere--Schiaparelli's Canals--Discovery
of Two Martian Satellites--Photographic Detection of Minor
Planets--Orbit of Eros--Distribution of the Minor Planets--Their
Collective Mass and Estimated Diameters--Condition of Jupiter--His
Spectrum--Transits of his Satellites--Discovery of a Fifth
Satellite--The Great Red Spot--Constitution of Saturn's Rings--Period
of Rotation of the Planet--Variability of Japetus--Equatorial Markings
on Uranus--His Spectrum--Rotation of Neptune--Trans-Neptunian
Planets 274

CHAPTER IX

THEORIES OF PLANETARY EVOLUTION

Origin of the World according to Kant--Laplace's Nebular
Hypothesis--Maintenance of the Sun's Heat--Meteoric
Hypothesis--Radiation as an Effect of Contraction--Regenerative
Theory--Faye's Scheme of Planetary Development--Origin of the
Moon--Effects of Tidal Friction 308

CHAPTER X

RECENT COMETS

Donati's Comet--The Earth again Involved in a Comet's Tail--Comets of
the August and November Meteors--Star Showers--Comets and
Meteors--Biela's Comet and the Andromedes--Holmes's Comet--Deflection
of the Leonids--Orbits of Meteorites--Meteors with Stationary
Radiants--Spectroscopic Analysis of Cometary Light--Comet of
1901--Coggia's Comet 323

CHAPTER XI

RECENT COMETS--(_continued_)

Forms of Comets' Tails--Electrical Repulsion--Brédikhine's Three
Types--Great Southern Comet--Supposed Previous Appearances--Tebbutt's
Comet and the Comet of 1807--Successful Photographs--Schaeberle's
Comet--Comet Wells--Sodium Blaze in Spectrum--Great Comet of
1882--Transit across the Sun--Relation to Comets of 1843 and
1880--Cometary Systems--Spectral Changes in Comet of 1882--Brooks's
Comet of 1889--Swift's Comet of 1892--Origin of Comets 345

CHAPTER XII

STARS AND NEBULÆ

Stellar Chemistry--Four Orders of Stars--Their Relative Ages--Gaseous
Stars--Spectroscopic Star-Catalogues--Stellar Chemistry--Hydrogen
Spectrum in Stars--The Draper Catalogue--Velocities of Stars in Line
of Sight--Spectroscopic Binaries--Eclipses of Algol--Catalogues of
Variables--New Stars--Outbursts in Nebulæ--Nova Aurigæ--Nova
Persei--Gaseous Nebulæ--Variable Nebulæ--Movements of Nebulæ--Stellar
and Nebular Photography--Nebulæ in the Pleiades--Photographic
Star-charting--Stellar Parallax--Double Stars--Stellar
Photometry--Status of Nebulæ--Photographs and Drawings of the Milky
Way--Star Drift 372

CHAPTER XIII

METHODS OF RESEARCH

Development of Telescopic Power--Silvered Glass Reflectors--Giant
Refractors--Comparison with Reflectors--The Yerkes
Telescope--Atmospheric Disturbance--The Lick Observatory--Mechanical
Difficulties--The Equatoreal _Coudé_--The Photographic
Camera--Retrospect and Conclusion 428