A POPULAR HISTORY OF ASTRONOMY DURING THE NINETEENTH CENTURY BY THE SAME AUTHOR PROBLEMS IN ASTROPHYSICS. Demy 8vo., cloth. Containing over 100 Illustrations. Price 20s. net. THE SYSTEM OF THE STARS. Second Edition. Thoroughly revised and largely rewritten. Containing numerous and new Illustrations. Demy 8vo., cloth. Price 20s. net. MODERN COSMOGONIES. Crown 8vo., cloth. Price 3s. 6d. net. A. AND C. BLACK, SOHO SQUARE, LONDON, W.[Pg i] [Pg ii] THE GREAT NEBULA IN ORION, 1883 See p. 408 [Pg iii] A POPULAR HISTORY OF ASTRONOMY DURING THE NINETEENTH CENTURY BY AGNES M. CLERKE JUPITER 1879 SATURN 1885 LONDON ADAM AND CHARLES BLACK 1908 [Pg iv] First Edition, Post 8vo., published 1885 Second Edition, Post 8vo., published 1887 Third Edition, Demy 8vo., published 1893 Fourth Edition, Demy 8vo., published 1902 Fourth Edition, Post 8vo., reprinted February, 1908 PREFACE TO THE FOURTH EDITION Since the third edition of the present work issued from the press, the nineteenth century has run its course and finished its record. A new era has dawned, not by chronological prescription alone, but to the vital sense of humanity. Novel thoughts are rife; fresh impulses stir the nations; the soughing of the wind of progress strikes every ear. "The old order changeth" more and more swiftly as mental activity becomes intensified. Already many of the scientific doctrines implicitly accepted fifteen years ago begin to wear a superannuated aspect. Dalton's atoms are in process of disintegration; Kirchhoff's theorem visibly needs to be modified; Clerk Maxwell's medium no longer figures as an indispensable factotum; "absolute zero" is known to be situated on an asymptote to the curve of cold. Ideas, in short, have all at once become plastic, and none more completely so than those relating to astronomy. The physics of the heavenly bodies, indeed, finds its best opportunities in unlooked-for disclosures; for it deals with transcendental conditions, and what is strange to terrestrial experience may serve admirably to expound what is normal in the skies. In celestial science especially, facts that appear subversive are often the most illuminative, and the prospect of its advance widens and brightens with each divagation enforced or permitted from the strait paths of rigid theory. This readiness for innovation has undoubtedly its dangers and drawbacks. To the historian, above all, it presents frequent occasions of embarrassment. The writing of history is a strongly selective operation, the outcome being valuable just in so far as the choice what to reject and what to include has been judicious; and the task is no light one of discriminating between barren speculations and ideas pregnant with coming truth. To the possession of[Pg vi] such prescience of the future as would be needed to do this effectually I can lay no claim; but diligence and sobriety of thought are ordinarily within reach, and these I shall have exercised to good purpose if I have succeeded in rendering the fourth edition of A Popular History of Astronomy during the Nineteenth Century not wholly unworthy of a place in the scientific literature of the twentieth century. My thanks are due to Sir David Gill for the use of his photograph of the great comet of 1901, which I have added to my list of illustrations, and to the Council of the Royal Astronomical Society for the loan of glass positives needed for the reproduction of those included in the third edition. London, July, 1902. [Pg vii] 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[Pg viii] 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[Pg ix] 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. [Pg x] [Pg xi] CONTENTS INTRODUCTION Three Kinds of Astronomy—Progress of the Science during the Eighteenth Century— Popularity and Rapid Advance during the Nineteenth Century 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 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 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 [Pg xii] 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 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 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 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 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 [Pg xiii] 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 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 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 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 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 [Pg xiv] 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 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 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 CHAPTER XI [...]... in an ample liberality The first regular observatory in the Southern Hemisphere was founded at Paramatta by Sir Thomas Makdougall Brisbane in 1821 The Royal Observatory at the Cape of Good Hope was completed in 1829 Similar establishments were set to work by the East India Company at Madras, Bombay, and St Helena, during the first third of the nineteenth century The organisation of astronomy in the. .. parallax" of the fixed stars was in effect answered With their annual parallax, however, the case was very different The search for it had already led Bradley to the important discoveries of the aberration of light and the nutation of the earth's axis; it was now about to lead Herschel to a discovery of a different, but even more elevated character Yet in neither case was the object primarily sought attained... and that the failure of repeated attempts to measure stellar parallaxes pointed to distances at least 400,000 times that of the earth from the sun,[7] the[ Pg 11] picture of sidereal science, when the last quarter of the eighteenth century began, is practically complete It included three items of information: that the stars have motions, real or apparent; that they are immeasurably remote; and that a few... since the dawn of civilisation A vast widening of the scope of astronomy has accompanied, and in part occasioned, the great extension of its area of cultivation which our age has witnessed In the last century its purview was a comparatively narrow one Problems lying beyond the range of the solar system were almost unheeded, because they seemed inscrutable Herschel first showed the sidereal universe as accessible... original position at the end of a year Bradley's second great discovery was finally ascertained in 1748 Nutation is a real "nodding" of the terrestrial axis produced by the dragging of the moon at the terrestrial equatorial protuberance From it results an apparent displacement of the stars, each of them describing a little ellipse about its true or "mean" position, in a period of nearly nineteen years... workmanship Thus practical and theoretical astronomy advanced on parallel lines in England and France respectively, the improvement of their several tools the telescope and the quadrant on the one side, and the calculus on the other—keeping pace The whole future of the science seemed to be theirs The cessation of interest through a too speedy attainment of the perfection towards which each spurred the. .. quarter of a century, of orbital revolution in the case of as many as fifty double stars, henceforth, he declared, to be held as real binary combinations, "intimately held together by the bond of mutual attraction."[34] The fortunate preservation in Dr Maskelyne's note-book of a remark made by Bradley about 1759, to the effect that the line joining the components of Castor was an exact prolongation of. .. Bradley in 1748, and Lambert in 1761, pointed out that such apparent displacements (by that time well ascertained) were in all probability a combined effect of motions both of sun and stars; and Mayer actually attempted the analysis, but without result On the 13th of August, 1596, David Fabricius, an unprofessional astronomer in East Friesland, saw in the neck of the Whale a star of the third magnitude, which... of astronomy in the eighteenth century ran in general an even and logical course The age succeeding Newton's had for its special task to demonstrate the universal validity, and trace the complex results, of the law of gravitation The accomplishment of that task occupied just one hundred years It was virtually brought to a close when Laplace explained to the French Academy, November 19, 1787, the cause... objects known as "nebulæ." The history of the acquaintance of our race with them is comparatively short The only one recognised before the invention of the telescope was that in the girdle of Andromeda, certainly familiar in the middle of the tenth century to the Persian astronomer Abdurrahman Al-Sûfi; and marked with dots on Spanish and Dutch constellation-charts of the fourteenth and fifteenth centuries.[40] . 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& quot;. Century Popularity and Rapid Advance during the Nineteenth Century PART I PROGRESS OF ASTRONOMY DURING THE FIRST HALF OF THE NINETEENTH CENTURY CHAPTER I FOUNDATION OF SIDEREAL ASTRONOMY State of Knowledge. scope of astronomy has accompanied, and in part occasioned, the great extension of its area of cultivation which our age has witnessed. In the last century its purview was a comparatively narrow