Thenceforth for many years he studied and reflected, but it
was not until the year of his death (1543) that his results were
published to the world. His book--_On the Revolutions of the
Celestial Bodies_, dedicated to Pope Paul III--offered the theory
that the earth is not the center of the universe but simply one of a
number of planets which revolve about the sun. The earth seemed much
less important in the Copernican universe than in the Ptolemaic.
The Copernican thesis was supported and developed by two distinguished
astronomers at the beginning of the next century--Kepler (1571-1630)
and Galileo (1564-1642), one a German, the other an Italian. Kepler
taught astronomy for a number of years at Gratz and subsequently made
his home in Prague, where he acquired a remarkable collection of
instruments [Footnote: From Tycho Brahe, whose assistant he was in
1600-1601.] that enabled him to conduct numerous interesting
experiments. While he entertained many fantastic and mystical theories
of the "harmony of the spheres" and was not above casting horoscopes
for the emperor and for Wallenstein, that soldier of fortune,
[Footnote: See below, pp.
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