h were at rest. The shifting position of the star
is very slight, and at the end of a year it returns to its former place.

Prior to the discovery of aberration, astronomers ascribed the apparent
displacement of the stars arising from this cause as being due to
parallax--a conclusion which led to erroneous results; but after
Bradley's discovery this source of error was avoided, and it was found
that the parallax of the stars had to be considerably reduced.

Bessel was the first astronomer who merited the high distinction of
having determined the first reliable stellar parallax, and by this
achievement he was enabled to fathom the profound abyss which separates
our solar system from the stars.

Frederick William Bessel was born in 1764 at Minden, in Westphalia. It
was his intention to pursue a mercantile career, and he commenced life
by becoming apprenticed to a firm of merchants at Bremen. Soon
afterwards he accompanied a trading expedition to China and the East
Indies, and while on this voyage picked up a good deal of information
with regard to many matters which came under his observation. He
acquired a knowledge of Spanish and English, and made himself acquainted
with the art of navigation. On his return home, Bessel endeavoured to
determine the longitude of Bremen. The only appliances which he made use
of were a sextant constructed by himself, and a common clock; and yet,
with those rude instruments, he successfully accomplished his object.
During the next two years he devoted all his spare time to the study of
mathematics and astronomy, and, having obtained possession of Harriot's
observations of the celebrated comet of 1607--known as Halley's
comet--Bessel, after much diligent application and careful calculation,
was enabled to deduce from them an orbit, which he assigned to that
remarkable body. This meritorious achievement was the means of procuring
for him a widely known reputation.

A vacancy for an assistant having occurred at Schroeter's Observatory at
Lilienthal, the post was offered to Bessel and accepted by him. Here he
remained for four years, and was afterwards appointed Director of the
new Prussian Observatory at Koenigsberg, where he pursued his
astronomical labours for a period of upwards of thirty years. Bessel
directed his energies chiefly to the study of stellar astronomy, and
made many observations in determining the number, the exact positions,
and proper motions of the stars. He was remarkab