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

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

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

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