a glimpse of the life history of the
remarkable man whose name they bear.

JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION

Johann Kepler was born the 27th of December, 1571, in the little town of
Weil, in Wurtemburg. He was a weak, sickly child, further enfeebled by a
severe attack of small-pox. It would seem paradoxical to assert that the
parents of such a genius were mismated, but their home was not a happy
one, the mother being of a nervous temperament, which perhaps in some
measure accounted for the genius of the child. The father led the life
of a soldier, and finally perished in the campaign against the Turks.
Young Kepler's studies were directed with an eye to the ministry. After
a preliminary training he attended the university at Tubingen, where
he came under the influence of the celebrated Maestlin and became his
life-long friend.

Curiously enough, it is recorded that at first Kepler had no taste
for astronomy or for mathematics. But the doors of the ministry being
presently barred to him, he turned with enthusiasm to the study of
astronomy, being from the first an ardent advocate of the Copernican
system. His teacher, Maestlin, accepted the same doctrine, though he was
obliged, for theological reasons, to teach the Ptolemaic system, as also
to oppose the Gregorian reform of the calendar.

The Gregorian calendar, it should be explained, is so called because it
was instituted by Pope Gregory XIII., who put it into effect in the year
1582, up to which time the so-called Julian calendar, as introduced by
Julius Caesar, had been everywhere accepted in Christendom. This Julian
calendar, as we have seen, was a great improvement on preceding ones,
but still lacked something of perfection inasmuch as its theoretical
day differed appreciably from the actual day. In the course of fifteen
hundred years, since the time of Caesar, this defect amounted to a
discrepancy of about eleven days. Pope Gregory proposed to correct this
by omitting ten days from the calendar, which was done in September,
1582. To prevent similar inaccuracies in the future, the Gregorian
calendar provided that once in four centuries the additional day to make
a leap-year should be omitted, the date selected for such omission being
the last year of every fourth century. Thus the years 1500, 1900, and
2300, A.D., would not be leap-years. By this arrangement an approximate
rectification of the calendar was effected, though even this does not
mak