[Illustration: PORTRAIT OF JOHANNES KEPLER. By F. Wanderer, from
Reitlinger's "Johannes Kepler" (original in Strassburg).]

It has seemed to many that Plato's demand for uniform circular motion
(linear or angular) was responsible for a loss to astronomy of good
work during fifteen hundred years, for a hundred ill-considered
speculative cosmogonies, for dissatisfaction, amounting to disgust,
with these _a priori_ guesses, and for the relegation of the
science to less intellectual races than Greeks and other Europeans.
Nobody seemed to dare to depart from this fetish of uniform angular
motion and circular orbits until the insight, boldness, and
independence of Johann Kepler opened up a new world of thought and of
intellectual delight.

While at work on the Rudolphine tables he used the old epicycles and
deferents and excentrics, but he could not make theory agree with
observation. His instincts told him that these apologists for uniform
motion were a fraud; and he proved it to himself by trying every
possible variation of the elements and finding them fail. The number
of hypotheses which he examined and rejected was almost incredible
(for example, that the planets turn round centres at a little distance
from the sun, that the epicycles have centres at a little distance
from the deferent, and so on). He says that, after using all these
devices to make theory agree with Tycho's observations, he still found
errors amounting to eight minutes of a degree. Then he said boldly
that it was impossible that so good an observer as Tycho could have
made a mistake of eight minutes, and added: "Out of these eight
minutes we will construct a new theory that will explain the motions
of all the planets." And he did it, with elliptic orbits having the