be done with them, however, Tycho died at the end of October, 1601. He
may have regretted the peaceful island of Hveen, considering the
troubles in which Bohemia was rapidly becoming involved, but there is
little doubt that had it not been for his self-imposed exile, his
observations would not have come into Kepler's hands, and their great
value might have been lost. In any case it was at Uraniborg that the
mass of observations was produced upon which the fame of Tycho Brahe
rests. His own discoveries, though in themselves the most important made
in astronomy for many centuries, are far less valuable than those for
which his observations furnished the material. He discovered the third
and fourth inequalities of the moon in longitude, called respectively
the variation and the annual equation, also the variability of the
motion of the moon's nodes and the inclination of its orbit to the
ecliptic. He obtained an improved value of the constant of precession,
and did good service by rejecting the idea that it was variable, an idea
which, under the name of trepidation, had for many centuries been
accepted. He discovered the effect of refraction, though only
approximately its amount, and determined improved values of many other
astronomical constants, but singularly enough made no determination of
the distance of the sun, adopting instead the ancient and erroneous
value given by Hipparchus.

His magnificent Observatory of Uraniborg, the finest building for
astronomical purposes that the world had hitherto seen, was allowed to
fall into decay, and scarcely more than mere indications of the site may
now be seen.