An astronomical observatory, in the general acceptation of the word, is
a building erected for the reception and appropriate use of astronomical
instruments, and the accommodation of the men of science employed
in making and reducing observations of the heavenly bodies. These
instruments are mainly of three classes, to which I believe all others
of a strictly astronomical character may be referred.
1. The instruments by which the heavens are inspected, with a view to
discover the existence of those celestial bodies which are not visible
to the naked eye (beyond all comparison more numerous than those which
are), and the magnitude, shapes, and other sensible qualities, both of
those which are and those which are not thus visible to the unaided
sight. The instruments of this class are designated by the general name
of Telescope, and are of two kinds,--the refracting telescope, which
derives its magnifying power from a system of convex lenses; and the
reflecting telescope, which receives the image of the heavenly body upon
a concave mirror.
2d. The second class of instruments consists of those which are designed
principally to measure the angular distances of the heavenly bodies
from each other, and their time of passing the meridian. The transit
instrument, the meridian circle, the mural circle, the heliometer,
and the sextant, belong to this class. The brilliant discoveries
of astronomy are, for the most part, made with the first class of
instruments; its practical results wrought out by the second.
3d. The third class contains the clock, with its subsidiary apparatus,
for measuring the time and making its subdivisions with the greatest
possible accuracy; indispensable auxiliary of all the instruments, by
which the positions and motions of the heavenly bodies are observed, and
measured, and recorded.