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Page:Popular Science Monthly Volume 56.djvu/303

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APPLETONS’

POPULAR SCIENCE

MONTHLY.

 

JANUARY, 1900.



ADVANCE OF ASTRONOMY DURING THE NINETEENTH CENTURY.
By Sir ROBERT BALL,

LOWNDEAN PROFESSOR OF ASTRONOMY AT THE UNIVERSITY OF CAMBRIDGE, ENGLAND.

ONE of the most remarkable chapters in the astronomy of the past century was commenced on the very first night with which that century began. It was, indeed, on the 1st of January, 1801, that the discovery of a new planet was announced. The five great orbs—Jupiter, Saturn, Mercury, Mars, and Venus—had been known from the earliest times of which we have records, and the planet Uranus had been discovered nearly twenty years before the previous century closed. The solar system was thus thought to consist of these six planets and, of course, the earth. On the memorable night to which I have referred, Piazzi, the astronomer, made a remarkable advance. He discovered yet another planet—the seventh, or eighth, if the earth be included. The new body was a small object in comparison with those which were previously known. It was invisible to the unaided eye, and seemed no more than a starlike point even when viewed through a telescope. It revolved around the sun in the wide region between the orbits of Mars and Jupiter. This discovery was speedily followed by others of the same kind, and, as the century has advanced to its close, the numbers of these planets—asteroids, as they are generally called—has been gradually increasing, so much so that now, of these little bodies known to astronomers, the number amounts to about four hundred and fifty.

But just as the beginning of the century was heralded by the discovery of the first of these asteroids, so the close of the century