It may be well before attempting to obtain a glimpse of recent progress
that we should try to grasp the state of the science at the time when
the nineteenth century was about to dawn, and this, perhaps, can be
best accomplished by seeing what men were working at this period, at
which the greatest activity was to be found in Germany; there was
no permanent observatory in the southern hemisphere or in the United
States.
First and foremost among the workers—he has, in fact, been described
as “the greatest of modern astronomers”—was William Herschel, a German
domiciled in England. In the year 1773 he hired a telescope, and with
this small instrument he obtained his first glimpses of the rich fields
of exploration open in the skies. From that time onward he had one
fixed purpose in his mind, which was to obtain as intimate knowledge as
possible of the construction of the heavens.
To do this, of course, great optical power was necessary, and such was
his energy that, as large instruments were not to be obtained at any
price, he set to work and made them himself.
Herschel presented the beginning of the nineteenth century not only
with a definite idea of the constitution of the stellar system, based
on a connected body of facts and deductions from facts, as gleaned
through his telescopes, but observations without number in many fields.
He discovered a new planet, Uranus, and several satellites of the
planets; published catalogues of nebulæ; established the gravitational
bond between many “double stars,” and carried on observations of the
sun, then supposed to be a habitable globe. What Herschel did for
observational astronomy and deductions therefrom, Laplace did for the
furtherance of our knowledge concerning the exact motions of the bodies
comprising the solar system. Newton had long before announced that
gravitation was universal, and Laplace brought together investigations
undertaken to determine the validity of this law. These were given to
the world in his wonderful book on _Celestial Mechanics_, the first
volumes of which appeared in 1799.
A survey of the work of these two great astronomers gives one an idea
of what was going on in observational and mathematical astronomy at
the beginning of the century.
The study was now destined to make rapid strides, as not only were new
optical instruments—some designed for special purposes—introduced,
new mathematical processes applied, fresh fields for research
opened up, but the number of workers was considerably augmented by
the increased means available; so much so, indeed, that the first
astronomical periodical was founded by Von Zach in 1800 to facilitate
intercommunications between the observers.
The first evening of the nineteenth century (January 1, 1801) augured
well for progress. It had long been thought that all the members of
the solar system had not as yet been discovered, and there was a very
notable gap between the planets Mars and Jupiter, indicated by Bode’s
law. Observers were organized to make a thorough search for the missing
planet, portions of the sky being divided between them for minute
examination. It fell to the Italian observer, Piazzi, to discover a
small body which was moving in an orbit between these two planets on
the date named. The century thus began with a sensation, and because
the new body, which was named “Ceres,” was not of sufficient size to be
accepted as the “missing planet,” the idea was suggested that perhaps
it was a fragment of a larger planet that had been blown to pieces in
the past.
An opportunity here arose for mathematical astronomy to come to the
help of the observer, for Ceres soon was lost in the solar rays, and in
order to rediscover it, after it had passed conjunction, an approximate
knowledge of its path and future position was necessary.
With the then existing methods of computation of orbits it was
imperative to have numerous measured positions to use as data for the
calculation. The scanty data available in the case of Ceres were not
sufficient for the application of the method. The occasion discovered a
man, one of the greatest mathematicians of the nineteenth century, Karl
Frederick Gauss, who, although only twenty-five years of age, undertook
the solution of the problem by employing a system which he had devised,
known as “the method of least squares,” which enabled him to obtain a
most probable result from a given set of observations.
This, with a more general method of orbit computation, also elaborated
by himself, was sufficient to enable him to calculate future positions
of Ceres, and on the anniversary of the original discovery, Olbers,
another great pioneer in orbit calculations, found the planet in very
nearly the position assigned by Gauss. So great was the curiosity
regarding the other portions of the planet, which was supposed to have
been shattered, that numerous observers at once commenced to search
after other fragments.
These were the _actualities_ of 1801 and thereabouts; but the seed
of much future work was sown. Kant and Laplace had already occupied
themselves with theories as to the world formation, and spectrum
analysis as applied to the heavenly bodies may be said to have been
started by Wollaston’s observations of dark lines in the solar spectrum
in 1802. Fraunhofer was then a boy at school. In the same year the
first photographic prints were produced by Wedgewood and Davy.