in
1607, in his _Mercurius in Sole visus_; but when Galileo, a few years
afterwards, discovered a great number of similar spots with the
telescope, Kepler retracted his opinions, and acknowledged that
Galileo's discovery afforded an explanation, also, of many similar
observations in old writers, which he had found it difficult to
reconcile with the actual motions of Mercury.

[50] It is said that Kepler saw this dark spot _while looking at
the sun in a camera obscura_. As a camera obscura is actually a
telescope, magnifying objects in proportion to the focal length of
the lens employed, he may be said to have first seen these spots
with the aid of an optical instrument.

Kepler was not one of those cold-hearted men who, though continually
occupied in the study of the material world, and ambitious of the
distinction which a successful examination of it confers, are yet
insensible to the goodness and greatness of the Being who made and
sustains it. His mind was cast in a better mould. The magnificence and
harmony of the divine works excited in him not only admiration but love.
He felt his own humility the farther he was allowed to penetrate into
the mysteries of the universe; and sensible of the incompetency of his
unaided powers for such transcendent researches, and recognising himself
as but the instrument which the Almighty employed to make known his
wonders, he never entered upon his inquiries without praying for
assistance from above. This frame of mind was by no means inconsistent
with that high spirit of delight and triumph with which Kepler surveyed
his discoveries. His was the unpretending ovation of success, not the
ostentatious triumph of ambition; and if a noble pride did occasionally
mingle itself with his feelings, it was the pride of being the chosen
messenger of physical truth, not that of being the favoured possessor of
superior genius. With such a frame of mind, Kepler was necessarily a
Christian. The afflictions with which he was beset confirmed his faith
and brightened his hopes: he bore them in all their variety and severity
with Christian patience; and though he knew that this world was to be
the theatre of his intellectual glory, yet he felt that his rest and his
reward could be found only in another.

It is difficult to form any very intelligible idea of the nature and
extent of Kepler's astrological opinions, and of the degree of credit
which he himself placed in the o