ich we shall
refer presently. The Landgrave of Hesse was a practical astronomer, who
produced a catalogue of fixed stars which has been compared with that
of Tycho Brahe. He was assisted by Rothmann and by Justus Byrgius.
Maestlin, the preceptor of Kepler, is reputed to have been the first
modern observer to give a correct explanation of the light seen on
portions of the moon not directly illumined by the sun. He explained
this as not due to any proper light of the moon itself, but as light
reflected from the earth. Certain of the Greek philosophers, however,
are said to have given the same explanation, and it is alleged also that
Leonardo da Vinci anticipated Maestlin in this regard.(2)

While, various astronomers of some eminence thus gave support to the
Copernican system, almost from the beginning, it unfortunately chanced
that by far the most famous of the immediate successors of Copernicus
declined to accept the theory of the earth's motion. This was Tycho
Brahe, one of the greatest observing astronomers of any age. Tycho
Brahe was a Dane, born at Knudstrup in the year 1546. He died in 1601 at
Prague, in Bohemia. During a considerable portion of his life he found
a patron in Frederick, King of Denmark, who assisted him to build a
splendid observatory on the Island of Huene. On the death of his patron
Tycho moved to Germany, where, as good luck would have it, he came in
contact with the youthful Kepler, and thus, no doubt, was instrumental
in stimulating the ambitions of one who in later years was to be known
as a far greater theorist than himself. As has been said, Tycho rejected
the Copernican theory of the earth's motion. It should be added,
however, that he accepted that part of the Copernican theory which
makes the sun the centre of all the planetary motions, the earth being
excepted. He thus developed a system of his own, which was in some sort
a compromise between the Ptolemaic and the Copernican systems. As Tycho
conceived it, the sun revolves about the earth, carrying with it the
planets-Mercury, Venus, Mars, Jupiter, and Saturn, which planets have
the sun and not the earth as the centre of their orbits. This cosmical
scheme, it should be added, may be made to explain the observed motions
of the heavenly bodies, but it involves a much more complex mechanism
than is postulated by the Copernican theory.

Various explanations have been offered of the conservatism which held
the great Danish astronomer back fr