lapse
of about thirty thousand years the elements of the orbits of these two
planets recover their original values.

II. THE PROGRESS OF MODERN ASTRONOMY

A NEW epoch in astronomy begins with the work of William Herschel, the
Hanoverian, whom England made hers by adoption. He was a man with a
positive genius for sidereal discovery. At first a mere amateur in
astronomy, he snatched time from his duties as music-teacher to grind
him a telescopic mirror, and began gazing at the stars. Not content with
his first telescope, he made another and another, and he had such genius
for the work that he soon possessed a better instrument than was ever
made before. His patience in grinding the curved reflective surface was
monumental. Sometimes for sixteen hours together he must walk steadily
about the mirror, polishing it, without once removing his hands.
Meantime his sister, always his chief lieutenant, cheered him with her
presence, and from time to time put food into his mouth. The telescope
completed, the astronomer turned night into day, and from sunset to
sunrise, year in and year out, swept the heavens unceasingly, unless
prevented by clouds or the brightness of the moon. His sister sat always
at his side, recording his observations. They were in the open air,
perched high at the mouth of the reflector, and sometimes it was so cold
that the ink froze in the bottle in Caroline Herschel's hand; but the
two enthusiasts hardly noticed a thing so common-place as terrestrial
weather. They were living in distant worlds.

The results? What could they be? Such enthusiasm would move mountains.
But, after all, the moving of mountains seems a liliputian task compared
with what Herschel really did with those wonderful telescopes. He moved
worlds, stars, a universe--even, if you please, a galaxy of universes;
at least he proved that they move, which seems scarcely less wonderful;
and he expanded the cosmos, as man conceives it, to thousands of times
the dimensions it had before. As a mere beginning, he doubled the
diameter of the solar system by observing the great outlying planet
which we now call Uranus, but which he christened Georgium Sidus,
in honor of his sovereign, and which his French contemporaries, not
relishing that name, preferred to call Herschel.

This discovery was but a trifle compared with what Herschel did later
on, but it gave him world-wide reputation none the less. Comets and
moons aside, this was the firs