the planet and the centre of the
Sun, describes equal areas in equal times. The third law, which relates
to the connection between the periodic times and the distances of the
planets, was not discovered until ten years later, when Kepler, in 1619,
issued another work, called the 'Harmonies of the World,' dedicated to
James I. of England, in which was contained this remarkable law. These
laws have elevated astronomy to the position of a true physical science,
and also formed the starting-point of Newton's investigations which led
to the discovery of the law of gravitation. Kepler's delight on the
discovery of his third law was unbounded. He writes: 'Nothing holds me.
I will indulge in my sacred fury. I will triumph over mankind by the
honest confession that I have stolen the golden vases of the Egyptians
to build up a tabernacle for my God far away from the confines of Egypt.
If you forgive me, I rejoice; if you are angry, I can bear it. The die
is cast; the book is written, to be read either now or by posterity I
care not which. It may well wait a century for a reader, as God has
waited six thousand years for an observer.'

When Kepler presented his celebrated book to the Emperor, he remarked
that it was his intention to make a similar attack upon the other
planets, and promised that he would be successful if his Majesty would
undertake to find the means necessary for carrying on operations. But
the Emperor had more formidable enemies to contend with nearer home than
Jupiter and Saturn, and no funds were forthcoming to assist Kepler in
his undertaking.

The chair of mathematics in the University of Linz having become vacant,
Kepler offered himself as a candidate for the appointment, which he was
anxious to obtain; but the Emperor Rudolph was averse to his leaving
Prague, and encouraged him to hope that the arrears of his salary would
be paid. But past experience led Kepler to have no very sanguine
expectations on this point; nor was it until after the death of Rudolph,
in 1612, that he was relieved from his pecuniary embarrassments.

On the accession of Rudolph's brother, Matthias, to the Austrian throne,
Kepler was reappointed Imperial Mathematician; he was also permitted to
hold the professorship at Linz, to which he had been elected. Kepler was
not loth to remove from Prague, where he had spent eleven years harassed
by poverty and other domestic afflictions. Having settled with his
family at Linz, Kepler issued an