le for the precision
with which he carried out his observations, and for the accuracy which
characterised all his calculations.

In 1837 Bessel, by the exercise of his consummate skill, endeavoured to
solve a problem which for many years baffled the efforts of the ablest
astronomers, viz., the determination of the parallax of the fixed stars.
This had been so frequently attempted, and without success, that the
results of any new observations were received with incredulity before
their value could be ascertained.

Bessel was ably assisted by Joseph Frauenhofer, an eminent optician of
Munich, who constructed a magnificent heliometer for the Observatory at
Koenigsberg, and in its design introduced a principle which admirably
adapted it for micrometrical measurement.

The star selected by Bessel is a binary known as 61 Cygni, the
components being of magnitudes 5.5 and 6 respectively. It has a large
proper motion, which led him to conclude that its parallax must be
considerable.

This star will always be an object of interest to astronomers, as it was
the first of the stellar multitude that revealed to Bessel the secret of
its distance.

Bessel commenced his observations in October 1837, and continued them
until March 1840. During this time he made 402 measurements, and, before
arriving at a conclusive result, carefully considered every imaginable
cause of error, and rigorously calculated any inaccuracies that might
arise therefrom. Finally, he determined the parallax of the star to be
0''.3483--a result equivalent to a distance about 600,000 times that of
the Earth from the Sun. In 1842-43 M. Peters, of the Pulkova
Observatory, arrived at an almost similar result, having obtained a
parallax of 0''.349; but by more recent observations the parallax of the
star has been increased to about half a second.

About the same time that Bessel was occupied with his observation of 61
Cygni, Professor Henderson, of Edinburgh, when in charge of the
Observatory at the Cape of Good Hope, directed his attention to Alpha
Centauri, one of the brightest stars in the Southern Hemisphere. During
1832-33 he made a series of observations of the star, with the object
of ascertaining its mean declination; and, having been informed
afterwards of its large proper motion, he resolved to make an endeavour
to determine its parallax. This he accomplished after his return to
Scotland, having been appointed Astronomer Royal in that country. By an
ex