HISTORY OF ASTRONOMY DURING THE NINETEENTH CENTURY

_INTRODUCTION_

We can distinguish three kinds of astronomy, each with a different
origin and history, but all mutually dependent, and composing, in their
fundamental unity, one science. First in order of time came the art of
observing the returns, and measuring the places, of the heavenly bodies.
This was the sole astronomy of the Chinese and Chaldeans; but to it the
vigorous Greek mind added a highly complex geometrical plan of their
movements, for which Copernicus substituted a more harmonious system,
without as yet any idea of a compelling cause. The planets revolved in
circles because it was their nature to do so, just as laudanum sets to
sleep because it possesses a _virtus dormitiva_. This first and oldest
branch is known as "observational," or "practical astronomy." Its
business is to note facts as accurately as possible; and it is
essentially unconcerned with schemes for connecting those facts in a
manner satisfactory to the reason.

The second kind of astronomy was founded by Newton. Its nature is best
indicated by the term "gravitational"; but it is also called
"theoretical astronomy."[1] It is based on the idea of cause; and the
whole of its elaborate structure is reared according to the dictates of
a single law, simple in itself, but the tangled web of whose
consequences can be unravelled only by the subtle agency of an elaborate
calculus.

The third and last division of celestial science may properly be termed
"physical and descriptive astronomy." It seeks to know what the heavenly
bodies are in themselves, leaving the How? and the Wherefore? of their
movements to be otherwise answered. Now, such inquiries became possible
only through the invention of the telescope, so that Galileo was, in
point of fact, their originator. But Herschel first gave them a
prominence which the whole progress of science during the nineteenth
century served to confirm and render more exclusive. Inquisitions begun
with the telescope have been extended and made effective in unhoped-for
directions by the aid of the spectroscope and photographic camera; and a
large part of our attention in the present volume will be occupied with
the brilliant results thus achieved.

The unexpected development of this new physical-celestial science is the
leading fact in recent astronomical history. It was out of the regular
course of events. In the degree in which it has actually occurred it
could certainly not have been foreseen. It was a seizing of the prize by
a competitor who had hardly been thought qualified to enter the lists.
Orthodox astronomers of the old school looked with a certain contempt
upon observers who spent their nights in scrutinising the faces of the
moon and planets rather than in timing their transits, or devoted
daylight energies, not to reductions and computations, but to counting
and measuring spots on the sun. They were regarded as irregular
practitioners, to be tolerated perhaps, but certainly not encouraged.

The advance 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 of the moon's accelerated motion. As a mere machine, the solar
system, so far as it was then known, was found to be complete and
intelligible in all its parts; and in the _Mécanique Céleste_ its
mechanical perfections were displayed under a form of majestic unity
which fitly commemorated the successive triumphs of analytical genius
over problems amongst the most arduous ever dealt with by the mind of
man.

Theory, however, demands a practical test. All its data are derived from
observation; and their insecurity becomes less tolerable as it advances
nearer to perfection. Observation, on the other hand, is the pitiless
critic of theory; it detects weak points, and provokes reforms which may
be the beginnings of discovery. Thus, theory and observation mutually
act and react, each alternately taking the lead in the endless race of
improvement.

Now, while in France Lagrange and Laplace were bringing the
gravitational theory of the solar system to completion, work of a very
different kind, yet not less indispensable to the future welfare of
astronomy, was being done in England. The Royal Observatory at Greenwich
is one of the few useful institutions which date their origin from the
reign of Charles II. The leading position which it still occupies in the
science of celestial observation was, for near a century and a half
after its foundation, an exclusive one. Delambre remarked that, had all
other materials of the kind been destroyed, the Greenwich records alone
would suffice for the restoration of astronomy. The establishment was
indeed absolutely without a rival.[2] Systematic observations of sun,
moon, stars, and planets were during the whole of the eighteenth century
made only at Greenwich. Here materials were accumulated for the secure
correction of theory, and here refinements were introduced by which the
exquisite accuracy of modern practice in astronomy was eventually
attained.

The chief promoter of these improvements was James Bradley. Few men have
possessed in an equal degree with him the power of seeing accurately,
and reasoning on what they see. He let nothing pass. The slightest
inconsistency between what appeared and what was to be expected roused
his keenest attention; and he never relaxed his mental grip of a subject
until it had yielded to his persistent inquisition. It was to these
qualities that he owed his discoveries of the aberration of light and
the nutation of the earth's axis. The first was announced in 1729. What
is meant by it is that, owing to the circumstance of light not being
instantaneously transmitted, the heavenly bodies appear shifted from
their true places by an amount depending upon the ratio which the
velocity of light bears to the speed of the earth in its orbit. Because
light travels with enormous rapidity, the shifting is very slight; and
each star returns to its 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.

Now, an acquaintance with the fact and the laws of each of these minute
irregularities is vital to the progress of observational astronomy; for
without it the places of the heavenly bodies could never be accurately
known or compared. So that Bradley, by their detection, at once raised
the science to a higher grade of precision. Nor was this the whole of
his work. Appointed Astronomer-Royal in 1742, he executed during the
years 1750-62 a series of observations which formed the real beginning
of exact astronomy. Part of their superiority must, indeed, be
attributed to the co-operation of John Bird, who provided Bradley in
1750 with a measuring instrument of till then unequalled excellence. For
not only was the art of observing in the eighteenth century a peculiarly
English art, but the means of observing were furnished almost
exclusively by British artists. John Dollond, the son of a Spitalfields
weaver, invented the achromatic lens in 1758, removing thereby the chief
obstacle to the development of the powers of refracting telescopes;
James Short, of Edinburgh, was without a rival in the construction of
reflectors; the sectors, quadrants, and circles of Graham, Bird,
Ramsden, and Cary were inimitable by Continental 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 other, appeared to be the only
danger it held in store for them. When all at once, a rival stood by
their side--not, indeed, menacing their progress, but threatening to
absorb their popularity.

The rise of Herschel was the one conspicuous anomaly in the astronomical
history of the eighteenth century. It proved decisive of the course of
events in the nineteenth. It was unexplained by anything that had gone
before; yet all that came after hinged upon it. It gave a new direction
to effort; it lent a fresh impulse to thought. It opened a channel for
the widespread public interest which was gathering towards astronomical
subjects to flow in.

Much of this interest was due to the occurrence of events calculated to
arrest the attention and excite the wonder of the uninitiated. The
predicted return of Halley's comet in 1759 verified, after an
unprecedented fashion, the computations of astronomers. It deprived such
bodies for ever of their portentous character; it ranked them as
denizens of the solar system. Again, the transits of Venus in 1761 and
1769 were the first occurrences of the kind since the awakening of
science to their consequence. Imposing preparations, journeys to remote
and hardly accessible regions, official expeditions, international
communications, all for the purpose of observing them to the best
advantage, brought their high significance vividly to the public
consciousness; a result aided by the facile pen of Lalande, in rendering
intelligible the means by which these elaborate arrangements were to
issue in an accurate knowledge of the sun's distance. Lastly, Herschel's
discovery of Uranus, March 13, 1781, had the surprising effect of utter
novelty. Since the human race had become acquainted with the company of
the planets, no addition had been made to their number. The event thus
broke with immemorial traditions, and seemed to show astronomy as still
young and full of unlooked-for possibilities.

Further popularity accrued to the science from the sequel of a career so
strikingly opened. Herschel's huge telescopes, his detection by their
means of two Saturnian and as many Uranian moons, his piercing scrutiny
of the sun, picturesque theory of its constitution, and sagacious
indication of the route pursued by it through space; his discovery of
stellar revolving systems, his bold soundings of the universe, his
grandiose ideas, and the elevated yet simple language in which they were
conveyed--formed a combination powerfully effective to those least
susceptible of new impressions. Nor was the evoked enthusiasm limited to
the British Isles. In Germany, Schröter followed--_longo intervallo_--in
Herschel's track. Von Zach set on foot from Gotha that general
communication of ideas which gives life to a forward movement. Bode
wrote much and well for unlearned readers. Lalande, by his popular
lectures and treatises, helped to form an audience which Laplace himself
did not disdain to address in the _Exposition du Système du Monde_.

This great accession of public interest gave the impulse to the
extraordinarily rapid progress of astronomy in the nineteenth century.
Official patronage combined with individual zeal sufficed for the elder
branches of the science. A few well-endowed institutions could
accumulate the materials needed by a few isolated thinkers for the
construction of theories of wonderful beauty and elaboration, yet
precluded, by their abstract nature, from winning general applause. But
the new physical astronomy depends for its prosperity upon the favour of
the multitude whom its striking results are well fitted to attract. It
is, in a special manner, the science of amateurs. It welcomes the most
unpretending co-operation. There is no one "with a true eye and a
faithful hand" but can do good work in watching the heavens. And not
unfrequently, prizes of discovery which the most perfect appliances
failed to grasp, have fallen to the share of ignorant or ill-provided
assiduity.

Observers, accordingly, have multiplied; observatories have been founded
in all parts of the world; associations have been constituted for mutual
help and counsel. A formal astronomical congress met in 1789 at
Gotha--then, under Duke Ernest II. and Von Zach, the focus of German
astronomy--and instituted a combined search for the planet suspected to
revolve undiscovered between the orbits of Mars and Jupiter. The
Astronomical Society of London was established in 1820, and the similar
German institution in 1863. Both have been highly influential in
promoting the interests, local and general, of the science they are
devoted to forward; while functions corresponding to theirs have been
discharged elsewhere by older or less specially constituted bodies, and
new ones of a more popular character are springing up on all sides.

Modern facilities of communication have helped to impress more deeply
upon modern astronomy its associative character. The electric telegraph
gives a certain ubiquity which is invaluable to an observer of the
skies. With the help of a wire, a battery, and a code of signals, he
sees whatever is visible from any portion of our globe, depending,
however, upon other eyes than his own, and so entering as a unit into a
widespread organisation of intelligence. The press, again, has been a
potent agent of co-operation. It has mainly contributed to unite
astronomers all over the world into a body animated by the single aim of
collecting "particulars" in their special branch for what Bacon termed a
History of Nature, eventually to be interpreted according to the
sagacious insight of some one among them gifted above his fellows. The
first really effective astronomical periodical was the _Monatliche
Correspondenz_, started by Von Zach in the year 1800. It was followed in
1822 by the _Astronomische Nachrichten_, later by the _Memoirs_ and
_Monthly Notices_ of the Astronomical Society, and by the host of varied
publications which now, in every civilised country, communicate the
discoveries made in astronomy to divers classes of readers, and so
incalculably quicken the current of its onward flow.

Public favour brings in its train material resources. It is represented
by individual enterprise, and finds expression 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 United States of America
was due to a strong wave of popular enthusiasm. In 1825 John Quincy
Adams vainly urged upon Congress the foundation of a National
Observatory; but in 1843 the lectures on celestial phenomena of Ormsby
MacKnight Mitchel stirred an impressionable audience to the pitch of
providing him with the means of erecting at Cincinnati the first
astronomical establishment worthy the name in that great country. On the
1st of January, 1882, no less than one hundred and forty-four were
active within its boundaries.

The apparition of the great comet of 1843 gave an additional fillip to
the movement. To the excitement caused by it the Harvard College
Observatory--called the "American Pulkowa"--directly owed its origin;
and the example was not ineffective elsewhere. The United States Naval
Observatory was built in 1844, Lieutenant Maury being its first
Director. Corporations, universities, municipalities, vied with each
other in the creation of such institutions; private subscriptions poured
in; emissaries were sent to Europe to purchase instruments and to
procure instruction in their use. In a few years the young Republic was,
in point of astronomical efficiency, at least on a level with countries
where the science had been fostered 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 to investigation, and thereby
offered to science new worlds--majestic, manifold, "infinitely infinite"
to our apprehension in number, variety, and extent--for future conquest.
Their gradual appropriation has absorbed, and will long continue to
absorb, the powers which it has served to develop.

But this is not the only direction in which astronomy has enlarged, or
rather has levelled, its boundaries. The unification of the physical
sciences is perhaps the greatest intellectual feat of recent times. The
process has included astronomy; so that, like Bacon, she may now be said
to have "taken all knowledge" (of that kind) "for her province." In
return, she proffers potent aid for its increase. Every comet that
approaches the sun is the scene of experiments in the electrical
illumination of rarefied matter, performed on a huge scale for our
benefit. The sun, stars, and nebulæ form so many celestial laboratories,
where the nature and mutual relations of the chemical "elements" may be
tried by more stringent tests than sublunary conditions afford. The laws
of terrestrial magnetism can be completely investigated only with the
aid of a concurrent study of the face of the sun. The solar spectrum
will perhaps one day, by its recurrent modifications, tell us something
of impending droughts, famines, and cyclones.

Astronomy generalises the results of the other sciences. She exhibits
the laws of Nature working over a wider area, and under more varied
conditions, than ordinary experience presents. Ordinary experience, on
the other hand, has become indispensable to her progress. She takes in
at one view the indefinitely great and the indefinitely little. The
mutual revolutions of the stellar multitude during tracts of time which
seem to lengthen out to eternity as the mind attempts to traverse them,
she does not admit to be beyond her ken; nor is she indifferent to the
constitution of the minutest atom of matter that thrills the ether into
light. How she entered upon this vastly expanded inheritance, and how,
so far, she has dealt with it, is attempted to be set forth in the
ensuing chapters.


FOOTNOTES:

[Footnote 1: The denomination "physical astronomy," first used by
Kepler, and long appropriated to this branch of the science, has of late
been otherwise applied.]

[Footnote 2: _Histoire de l'Astronomie au xviii^e Siècle_, p. 267.]


A Popular History of Astronomy During the
Nineteenth Century, by Agnes M. (Agnes Mary) Clerke