from the earth to the sun; and he established the somewhat humiliating
truth, that our earth is merely a planet pursuing a track between the
paths of Venus and of Mars, and subordinated like all the other planets
to the supreme sway of the Sun.

This great revolution swept from astronomy those distorted views of the
earth's importance which arose, perhaps not unnaturally, from the fact
that we happen to be domiciled on that particular planet. The
achievements of Copernicus were soon to be followed by the invention of
the telescope, that wonderful instrument by which the modern science of
astronomy has been created. To the consideration of this important
subject we shall devote the first chapter of our book.

[Illustration: PLATE II.

A TYPICAL SUN-SPOT.

(AFTER LANGLEY.)]

CHAPTER I.

THE ASTRONOMICAL OBSERVATORY.

Early Astronomical Observations--The Observatory of Tycho
Brahe--The Pupil of the Eye--Vision of Faint Objects--The
Telescope--The Object-Glass--Advantages of Large Telescopes--The
Equatorial--The Observatory--The Power of a Telescope--Reflecting
Telescopes--Lord Rosse's Great Reflector at Parsonstown--How the
mighty Telescope is used--Instruments of Precision--The Meridian
Circle--The Spider Lines--Delicacy of pointing a
Telescope--Precautions necessary in making Observations--The Ideal
Instrument and the Practical One--The Elimination of
Error--Greenwich Observatory--The ordinary Opera-Glass as an
Astronomical Instrument--The Great Bear--Counting the Stars in the
Constellation--How to become an Observer.

The earliest rudiments of the Astronomical Observatory are as little
known as the earliest discoveries in astronomy itself. Probably the
first application of instrumental observation to the heavenly bodies
consisted in the simple operation of measuring the shadow of a post cast
by the sun at noonday. The variations in the length of this shadow
enabled the primitive astronomers to investigate the apparent movements
of the sun. But even in very early times special astronomical
instruments were employed which possessed sufficient accuracy to add to
the amount of astronomical knowledge, and displayed considerable
ingenuity on the part of the designers.

Professor Newcomb[2] thus writes: "The leader was Tycho Brahe, who was
born in 1546, three years after the death of Copernicus. His attention
was first directed to the study of as