with reference to measuring their distance, and his efforts had
been attended with considerable success. He did not, indeed, know
the actual distance of the sun, and, therefore, was quite unable
to fix the distance of any planet; but, on the other hand, he
determined the relative distance of all the planets then known,
as measured in terms of the sun's distance, with remarkable
accuracy.

With these measurements as a guide, Kepler was led to a very
fanciful theory, according to which the orbits of the five
principal planets sustain a peculiar relation to the five regular
solids of geometry. His theory was this: "Around the orbit of the
earth describe a dodecahedron--the circle comprising it will be
that of Mars; around Mars describe a tetrahedron--the circle
comprising it will be that of Jupiter; around Jupiter describe a
cube--the circle comprising it will be that of Saturn; now within
the earth's orbit inscribe an icosahedron--the inscribed circle
will be that of Venus; in the orbit of Venus inscribe an
octahedron --the circle inscribed will be that of Mercury."[3]

Though this arrangement was a fanciful one, which no one would
now recall had not the theorizer obtained subsequent fame on more
substantial grounds, yet it evidenced a philosophical spirit on
the part of the astronomer which, misdirected as it was in this
instance, promised well for the future. Tycho Brahe, to whom a
copy of the work was sent, had the acumen to recognize it as a
work of genius. He summoned the young astronomer to be his
assistant at Prague, and no doubt the association thus begun was
instrumental in determining the character of Kepler's future
work. It was precisely the training in minute observation that