THE

PRACTICAL ASTRONOMER,

COMPRISING

ILLUSTRATIONS OF LIGHT AND COLOURS-PRACTICAL
DESCRIPTIONS OF ALL KINDS OF TELESCOPES-

THE USE OF THE EQUATORIAL-TRANSIT-
CIRCULAR, AND OTHER ASTRONOMICAL
INSTRUMENTS,

A PARTICULAR ACCOUNT OF THE

EARL OF ROSSE'S LARGE TELESCOPES,

1stn508.45

PRINTED BY L. SEELEY.

MICROFILMED

AT HARVARD

PREFACE.

in

THE following work was announced several years ago the preface to the volume on "The Sidereal Heavens; since which time numerous enquiries have been made after it by correspondents in England, the West Indies, and America. It was nearly ready for publication three years ago; but circumstances over which the Author had no controul, prevented its appearance at that period. This delay, however, has enabled him to introduce descriptions of certain instruments and inventions which were partly unknown at the time to which he refers.

The title "Practical Astronomer" has been fixed upon, as the shortest that could be selected, although the volume does not comprise a variety of topics and discussions generally comprehended in this department of astronomy. The work is intended for the information of general readers, especially for those who have acquired a relish for astronomical pursuits, and who wish to become acquainted with the instruments by which celestial observations are made, and to apply their mechanical skill to the construction of some of those which they may wish to possess. With this view the Author has entered into a variety of minute details, in reference to the construction and practical application of all kinds

of telescopes, &c. which are not to be found in general
treatises on Optics and Astronomy.

As Light is the foundation of astronomical science,
and of all the instruments used for celestial observation,
a brief description is given of the general properties of
light of the laws by which it is refracted and reflected
when passing through different mediums-and of the
effects it produces in the system of nature-in order to
prepare the way for a clear understanding of the princi-
ples on which optical instruments are constructed, and
the effects they produce.

As this, as well as every other physical subject, forms
a part of the arrangements of the Creator throughout
the material system—the Author has occasionally taken
an opportunity of directing the attention of the reader
to the Wisdom and Beneficence of the Great First
Cause, and of introducing those moral reflections which
naturally flow from the subject.

The present is the ninth volume which the Author has
presented to the public, and he indulges the hope that
it will meet with the same favourable reception which
his former publications have uniformly experienced.
It was originally intended to conclude the volume with a
few remarks on the utility of astronomical studies, and
their moral and religious tendency, but this has been
prevented, for the present, in consequence of the work
having swelled to a greater size than was anticipated.
Should he again appear before the public as an author,
the subject of discussion and illustration will have a
more direct bearing than the present on the great
objects of religion and a future world.

Broughty Ferry, near Dundee, August, 1845.