A Century’s Progress
IN
Astronomy
BY
HECTOR MACPHERSON, Jun.
MEMBER OF THE SOCIÉTÉ ASTRONOMIQUE DE FRANCE;
MEMBER OF THE SOCIÉTÉ BELGE D’ASTRONOMIE;
AUTHOR OF ‘ASTRONOMERS OF TO-DAY’
WILLIAM BLACKWOOD AND SONS
EDINBURGH AND LONDON
MCMVI
_All Rights reserved_
PREFACE.
The present volume originated in a desire to present, in small compass,
a record of the marvellous progress in astronomy during the past hundred
years. Indebtedness should be acknowledged to the valuable works of
Professor Newcomb, Professor Schiaparelli, Professor Lowell, Professor
Young, Sir Robert Ball, Mr Gore, M. Flammarion, and Miss Clerke, who, as
the historian of modern astronomy, occupies a place at once
authoritative and unique.
Portions of Chapters II. and XII. have already appeared in the form of
an article on the Construction of the Heavens, contributed by the writer
to the American periodical, ‘Popular Astronomy.’
Balerno, Mid-Lothian,
_October 1906_.
CONTENTS.
PAGE
CHAPTER I. 1
HERSCHEL THE PIONEER.
Influence of Herschel’s work—His characteristics—Birth and
early years—Emigration to England—Caroline
Herschel—Discovery of Uranus—King’s Astronomer—Latter
years and death—Death of Caroline Herschel
CHAPTER II. 15
HERSCHEL THE DISCOVERER.
Solar researches—Study of Venus—Of Mars—The
Asteroids—Jupiter—Saturn—Discovery of satellites—Uranian
satellites—Cometary researches—Motion of the Solar
System—Discovery of binary stars—Clusters and
nebulæ—Nebulous stars—The Nebular
Hypothesis—Star-gauging—The disc-theory—Subordinate
clusters—Abandonment of the disc-theory—Second method of
star-gauging—Estimate of Herschel’s work
CHAPTER III. 43
THE SUN.
Schwabe and the sun-spot period—Researches of Wolf, Lamont,
Sabine, Gautier—Observations of Carrington and
Spörer—Career and work of Fraunhofer—Spectrum
analysis—Work of Kirchhoff—Solar eclipse work—The Solar
prominences—Janssen and Lockyer—Huggins and Zöllner—Work
of Young—The Italian spectroscopists, Secchi, Respighi,
Tacchini—Career of Tacchini—The reversing layer—The
Corona—Doppler’s principle—Rotation of the Sun—Work of
Dunér—Janssen’s solar atlas—Maunder and magnetism—Solar
theories—Distance of the Sun—Summary
CHAPTER IV. 65
THE MOON.
Life and work of Schröter—Of Mädler—Of Schmidt—Changes on the
Moon—Selenography in England—Lunar atmosphere—Lunar
photography—Work of W. H. Pickering—The new
Selenography—The Moon’s heat—Motion of the
Moon—Acceleration of the Moon’s mean motion—Work of
Laplace, Adams, Delaunay
CHAPTER V. 80
THE INNER PLANETS.
The problem of Vulcan—Mercury—Work of Schröter—Schiaparelli,
his life and work—Work of Lowell—Spectrum of
Mercury—Venus—Rotation period: work of Schröter, Di Vico,
Schiaparelli, Tacchini, Lowell—Atmosphere and surface of
Venus—The Earth: variation of latitude—Mars—Rotation of
Mars—Surface—Discovery of canals—Work of Schiaparelli and
Lowell—Interpretation of the canals—The theory of
intelligent life—Spectrum of Mars—Satellites—The
Asteroids—Bode’s law—Work of Piazzi and Olbers—Application
of photography by Wolf—Discovery of Eros
CHAPTER VI. 103
THE OUTER PLANETS.
Physical condition of Jupiter—Work of Zöllner and Proctor—The
red spot—Satellites—Discovery of fifth satellite—Sixth and
seventh satellites—Rings of Saturn: Bond, Maxwell,
Keeler—Struve’s theory—Globe of Saturn—New
satellites—Uranus and its satellites—Discovery of
Neptune—Adams and Le Verrier—Satellite—Trans-Neptunian
planets
CHAPTER VII. 123
COMETS.
Life and work of Olbers—His repulsion theory—Life and work of
Encke—His comet—Biela’s comet—Faye’s comet—Return of
Halley’s comet—Donati’s comet—Comet of 1861—Spectroscopic
study of comets—Theory of Brédikhine—Spectra of
comets—Comets of 1880 and 1882—The capture theory—Cometary
photography
CHAPTER VIII. 138
METEORS.
Meteoric shower of 1833—Work of Olmsted—Work of Erman and
Kirkwood—Of H. A. Newton—Adams and the meteoric
orbit—Shower of 1866—Connection of comets and meteors—Work
of Schiaparelli—Shower of meteors in 1872—‘Le Stelle
Cadenti’—Meteoric observation—A. S. Herschel—Work of
Denning—Stationary radiants—Bolides and aerolites—Origin
of aerolites
CHAPTER IX. 150
THE STARS.
Distance of the stars—Life and work of Bessel—Studies of
Struve—Life and work of Henderson—Work of Peters, Otto
Struve, Brünnow, and Ball—Measures of Gill—Parallax of
first-magnitude stars—Relative and absolute parallax—Work
of Kapteyn—Application of
photography—Star-catalogues—Argelander’s
‘Durchmusterung’—Work of Schönfeld—Work of Gould—The ‘Cape
Photographic Durchmusterung’—Work of Gill and
Kapteyn—International chart of the heavens—Work of
Peck—Proper motions of the stars—Star-drift—Discoveries of
Proctor and Flammarion—Radial motion—Work of Huggins,
Vogel, and Campbell—Solar motion
CHAPTER X. 169
THE LIGHT OF THE STARS.
Work of Fraunhofer and Donati—Life and work of Secchi—His
types of spectra—Life and work of Huggins—Photography of
spectra—Life and work of Vogel—His classification of
spectra—Work of Dunér—Of Pickering—Spectroscopic
catalogues—Analysis of spectra—Stellar photometry—Life and
work of E. C. Pickering—Variable stars—Work of
Goodricke—Of Argelander, Schmidt, Heis, Schönfeld—Studies
of Dunér—Of Gore—Photographic
discoveries—Classification—Algol variables: their
explanation—Explanation of other variables—η
Argus—Temporary stars—Of 1848—Of 1866—Of 1876—Of 1885—Of
1892—Photographic discoveries—Nova Persei, 1901—New star
of 1903—Theories of temporary stars
CHAPTER XI. 197
STELLAR SYSTEMS AND NEBULÆ.
Life and work of John Herschel—Binary stars—Computation of
orbits—Work of Wilhelm Struve—Of Otto Struve—Of
Burnham—Satellites of Sirius and Procyon—Astronomy of the
invisible—Work of Pickering and Vogel—Spectroscopic
binaries—Work of Bélopolsky and
Campbell—Star-clusters—Nature of nebulæ—Spectroscopic work
of Huggins—Of Copeland—Nebular photography—Work of
Roberts, Barnard, Wolf—Of Keeler
CHAPTER XII. 214
STELLAR DISTRIBUTION AND THE STRUCTURE OF THE UNIVERSE.
Work of John Herschel—Researches of Wilhelm Struve—Extinction
of light—Mädler’s “central sun”—Distribution of
nebulæ—Work of Proctor—Aggregation of stars on the
Galaxy—Work of Gore and Schiaparelli—Studies of
Gould—Researches of Kapteyn—Of Newcomb—Is the Universe
limited? Newcomb’s argument—Observations of
Celoria—Researches of Seeliger—External Universes—Gore’s
speculations
CHAPTER XIII. 227
CELESTIAL EVOLUTION.
Laplace’s nebular hypothesis—Helmholtz and solar
contraction—Theories of solar heat—Objections to Laplace’s
theory—Faye’s hypothesis—Ball’s exposition—The meteoritic
theory of Proctor—Its extension by Lockyer—Evolution of
the stars—Vogel’s order of evolution—Tidal friction: work
of Darwin—See’s explanation of double stars—Future of the
Universe
A CENTURY’S PROGRESS IN ASTRONOMY.
CHAPTER I.
HERSCHEL THE PIONEER.
In astronomy, as in other sciences, the past hundred years has been a
period of unparalleled progress. New methods have been devised, fresh
discoveries have been made, new theories have been propounded; the field
of work has widened enormously. In fact, the science of the heavens has
become not only boundless in its possibilities, but more awe-inspiring
and marvellous.
To whom in the main is this great advance due? To the great pioneer of
what may be called modern astronomy—William Herschel. Not only did
Herschel reconstruct the science and widen its bounds, but his powerful
genius directed the course of nineteenth century research. As an
astronomical observer he has never been surpassed. In the breadth of his
views he was equalled only by Newton; and indeed he excelled Newton in
his unwearied observations and his sweeping conceptions of the Universe.
To quote his own remark to the poet Campbell, he “looked farther into
space than ever human being did before him.”
Herschel studied astronomy in all its aspects. In all the branches of
modern astronomy he was a pioneer. He observed the Sun, Moon, and
planets, devoting special attention to Mars and Saturn. He doubled the
diameter of the Solar System by the discovery of Uranus. He discovered
several satellites and studied comets. He was pre-eminently the founder
of sidereal astronomy. He discovered binary stars, thus tracing the law
of gravitation in the distant star-depths; while to him is due the
credit of the discovery of the motion of the Solar System. He founded
the study of star-clusters and nebulæ, propounded the nebular
hypothesis, and devised two methods of star-gauging. Above all, he was
the first to attempt the solution of one of the noblest problems ever
attacked by man—the structure of the Universe. In fact, the latter
problem was the end and aim of his observations. As Miss Clerke remarks,
“The magnificence of the idea, which was rooted in his mind from the
start, places him apart from and above all preceding observers.” Most of
the departments of modern astronomy find a meeting-place in Herschel, as
the branches run to the root of the tree. He discussed astronomy from
every point of view. Before, however, proceeding to examine the work of
this great man, it is well to note a few of his characteristics. These
characteristics, once understood, give us the key to his researches.
Before we can master Herschel the astronomer we must understand Herschel
the man.
Notwithstanding the fact that Herschel spent most of his life in
England, and that he is included in the ‘Dictionary of National
Biography,’ he was pre-eminently a German. Like most Germans his style
of writing was somewhat obscure, and this was emphasised when he wrote
in English, owing to his imperfect command of the language. Had he
written in German as well as in English, he would probably have been
better understood in his native country, where erroneous views of his
theories were long entertained. Even so distinguished an astronomer as
Wilhelm Struve, when translating Herschel’s papers into German, made a
mistake when translating a certain passage, which leaves the erroneous
impression that Herschel believed the Universe to be infinite—a mistake
which would not have arisen had he written in German.
The student of Herschel should also be careful in quoting the views of
the great astronomer. Had Herschel at the close of his life written a
volume containing his final views on the construction of the heavens,
this would not have been necessary; but Herschel did not write such a
volume. His researches were embodied in a series of papers communicated
to the Royal Society from 1780 to 1818. As he observed the heavens his
opinions progressed, so that a statement of his views at any given time
was by no means a statement of his final opinions. The late R. A.
Proctor, who was the first great exponent of Herschel in England, has
well said: “It seems to have been supposed that his papers could be
treated as we might treat such a work as Sir J. Herschel’s ‘Outlines of
Astronomy’; that extracts might be made from any part of any paper
without reference to the position which the paper chanced to occupy in
the entire series.”
Herschel, like the true student of nature, held theories very lightly.
They were to him but roads to the truth. Unlike many scientists, he did
not interpret observations by hypothesis: he framed his theories to fit
his observations. If he found that a certain theory did not agree with
what he actually saw in the heavens, he abandoned it: he did not
hesitate to change his views as his investigations proceeded. “No fear
of ‘committing himself,’” says Miss Clerke in her admirable work on ‘The
Herschels,’ “deterred him from imparting the thoughts that accompanied
his multitudinous observations. He felt committed to nothing but truth.”
In the mind of Herschel imagination and observation were marvellously
blended. He was a philosophical astronomer. Although his imagination was
a very vivid one he did not allow his fancies to run away with him, as
Kepler sometimes did: on the other hand, he did not, like Flamsteed,
refrain from speculating altogether. “We ought,” he wrote in 1785, “to
avoid two opposite extremes. If we indulge a fanciful imagination, and
build worlds of our own, we must not wonder at our going wide from the
path of truth and nature. On the other hand, if we add observation to
observation, without attempting to draw not only certain conclusions but
also conjectural views from them, we offend against the very end for
which only observations ought to be made.”
These characteristics—the lightness with which he held his theories, his
vivid imagination, and his philosophical reasoning—are the secrets of
Herschel’s success as an astronomer. Nearly all his ideas and
speculations have been confirmed. As Arago has said, “We cannot but feel
a deep reverence for that powerful genius that has scarcely ever erred.”
Herschel, like all other great students of Nature, was deeply religious.
He could not observe the heavens without feeling awed at the marvels
which his telescopes revealed. In his own words, “It is surely a very
laudable thing to receive instruction from the Great Workmaster of
Nature.”
Friedrich Wilhelm Herschel, born in Hanover on November 15, 1738, was
the fourth child of Isaac Herschel, an oboist in the band of the
Hanoverian Guard. Isaac Herschel, a native of Dresden, was an
accomplished musician, and all his children, ten in number, inherited
his talent. Of these ten, six survived, and only two became famous.
These were William, the great astronomer, and his sister Caroline (born
on March 16, 1750), who became a student of the heavens only second to
her brother.
At the garrison school in Hanover, where the Herschels were educated,
William Herschel showed intense love and aptitude for learning, and was
more diligent and persevering than his brother Jacob, his senior by four
years. In 1753 he became oboist in the band of the Hanoverian Guard in
which his father was now bandmaster. In her valuable memoirs, his sister
relates that her father was very interested in astronomy, and that he
taught his children the names of the constellations. William became
devoted to the science, and constructed a small celestial globe on which
equator and ecliptic were engraved. But his studies were much hampered.
His mother had a great dislike to learning: she had no sympathy with
aspirations, and tried to prevent her children becoming well educated.
Above all, the Hanoverian Guard was ordered to England in 1755, when a
French invasion was feared, and to that country Herschel proceeded,
along with his father and brother.
Returning to Germany in 1756, the Hanoverian Guard was employed the
following year in the Seven Years’ War. Hanover was invaded by the
French, and, conscription being the rule, the musicians were not
exempted from service. Under the command of the Duke of Cumberland the
Guard suffered a terrible defeat at Hastenbeck. William Herschel spent
the night after the battle in a ditch, and decided that soldiering would
not be his profession. He deserted, and, with the consent of his
parents, he sailed for England. After his arrival at Dover, he wandered
through the country in search of musical employment. At length, in 1760,
he was appointed to train the band of the Durham Militia, and four years
later paid a secret visit to Hanover, where he was welcomed by his
father, whose health was now failing, and by his sister Caroline. In the
following year he was promoted to the post of organist at Halifax, and
in 1766 he removed to Bath as oboist in Linley’s Orchestra. Finally, in
1767, he became organist in the new Octagon Chapel at Bath. Herschel was
now twenty-nine years old, and known as a famous musician. As Miss
Clerke remarks: “The Octagon Chapel soon became a centre of fashionable
attraction, and he soon found himself lifted on the wave of public
favour. Pupils of high rank thronged to him, and his lessons often
mounted to thirty-five a-week.”
In the year of his appointment his father died, aged sixty, after a life
of trouble and hardship. His death was a great blow to his daughter
Caroline, whom he had educated when her mother was from home. Caroline
Herschel was naturally possessed of musical ability, but her mother and
elder brother had determined that she should be a housemaid,—a
determination which William, who was devotedly attached to his sister,
opposed. Finally, in 1772, he visited Hanover, and took his sister to
England with him to act as his housekeeper. But for her unwearied
devotion it is doubtful whether William Herschel would have become the
great astronomer.
About the time of his appointment in Bath Herschel commenced the study
of languages and mathematics, reading Maclaurin’s ‘Fluxions’ and
Ferguson’s ‘Astronomy.’ The perusal of the latter volume revived his
love for astronomy. After fourteen or sixteen hours’ teaching he would
retire to his bedroom and read of the wonders of the heavens. His
interest increased as he proceeded, until, in his own words, “I resolved
to take nothing upon trust, but to see with my own eyes all that other
men had seen before me.” Accordingly he hired a small reflector.
Inquiring the price of a larger instrument, he found it to be quite
beyond his means. Then in 1772, when his sister came to keep his house
for him, he resolved to make his own telescope. First he tried the
fitting of lenses into pasteboard tubes, but this being a total failure,
he bought the apparatus of a Quaker optician who had constructed, or
attempted to construct, reflecting telescopes. In June 1773, assisted by
his sister and by his brother Alexander, then in Bath, he commenced
work. His first speculum mirror was five inches in diameter; and, while
it was in process of construction, he was obliged to hold his hands on
it for sixteen hours at a stretch, while his sister supplied his food
and read ‘The Arabian Nights,’ ‘Don Quixote,’ and other tales aloud to
him to pass the time. At last, after two hundred failures, he finished a
5-inch reflector, and on March 4, 1774, he observed the Orion nebula. No
sooner had Herschel commenced his celestial explorations than he
resolved to survey the entire heavens, leaving no spot unvisited.
In 1775 he commenced his review of the heavens, but finding his
telescope inadequate he began the work of telescope-making afresh.
Meanwhile he had much to distract him from astronomy. In 1776 he became
director of the Public Concerts at Bath. Yet his enthusiasm was
unbounded: he would run to his house between the acts at the theatre to
observe the heavens. In 1779, when observing the Moon from the street in
front of his house, a gentleman asked permission to see the celestial
wonders, a request which Herschel granted. The gentleman, Dr Watson of
Bath, introduced Herschel to the Literary Society, and we find him in
1780 contributing two papers to the Royal Society on Mira Ceti and the
Moon. In the same year he commenced his second review of the heavens,
and during its progress he made his first great discovery. On March 13,
1781, while surveying the constellation Gemini, he discovered a faint
object distinguished by a disc, which he concluded to be a tailless
comet, but which was soon shown to be a new planet beyond the orbit of
Saturn. This was the first planetary discovery made within the memory of
man. King George III. summoned Herschel to London, and gave him a
pension of £200 a-year, with the title of King’s Astronomer, pardoning
him also for his desertion from the army more than twenty years
previously. Herschel then named the new planet the “Georgium Sidus,” a
title now abandoned and replaced by Uranus.
William and Caroline Herschel now moved to Datchet, near Windsor, in
1785 to Clay Hall, and finally, in 1786, to Slough,—“the spot of all the
world,” said Arago, “where the greatest number of discoveries have been
made.” Here Herschel and his sister worked for nearly forty years. He
communicated to the Royal Society paper after paper on astronomy in all
its aspects. He also continued the work of telescope-making, and
constructed, in 1789, his 40-foot reflector, the wonder of the age. In
1787 his sister was appointed his assistant, and together the Herschels
worked from dusk to dawn. Caroline Herschel herself detected eight
comets and numerous nebulæ. She relates in her memoirs that on one
occasion, while she was acting as assistant, the ink froze in her pen.
But such inconveniences mattered not to the Herschels. As Miss Clerke
has well remarked, “Every serene dark night was to him a precious
opportunity, availed of to the last minute. The thermometer might
descend below zero, ink might freeze, mirrors might crack; but, provided
the stars shone, he and his sister worked on from dusk to dawn.... On
one occasion he is said to have worked without intermission at the
telescope and the desk for seventy-two hours.”
Honours were showered on Herschel. He was knighted in 1816, and became
President of the Royal Astronomical Society in 1820, besides receiving
several honorary degrees. But honours in no way elated him. Advancing
years in no way affected his wonderful mind. But his duties as King’s
Astronomer necessitated his acting as “showman of the heavens” on the
visits of royalties to Windsor, often after a whole day’s work, when
rest was absolutely necessary. This tremendous strain, which reflects
little credit on the Court, proved too much for the old man. His health
began to give way, although his mind was as vigorous as ever.
Herschel contributed his last paper to the Royal Society in 1818, and
three years later sent a list of double stars to the new Astronomical
Society. He made his last observation on June 1, 1821. His strength had
now left him, and to this he could not reconcile himself. As Miss Clerke
puts it, “All his old instincts were still alive, only the bodily power
to carry out their behests was gone. An unparalleled career of
achievement left him unsatisfied with what he had done.... His strong
nerves were at last shattered.” After a prolonged period of failing
health he died at Slough, at the age of eighty-three, on August 25,
1822. On September 7 he was buried in the church-yard of St Laurence at
Upton. On his tombstone are engraved the words—“Cœlorum perrupit
claustra”—he broke through the barriers of the skies.
The death of her brother was a terrible blow to Caroline Herschel.
Expecting to live only a twelvemonth, she returned to Hanover to the
home of her brother, Dietrich Herschel. But she lived twenty-five years
among people who cared nothing for astronomy. She was delighted at Sir
John Herschel’s continuation of his father’s work. She compiled a
catalogue of all the clusters and nebulæ observed by her brother, for
which she received the gold medal of the Astronomical Society, and she
was created an honorary member. In 1846 she received from the King of
Prussia the gold medal of science. But no honours made her in any way
elated. She always held that whoever said much of her said too little of
her brother. After a prolonged decline of health, she died on January 9,
1848, aged ninety-seven years, and was buried beside her father in the
churchyard of the Gartengemeinde at Hanover, leaving behind her a noble
example of self-sacrifice and devotion.