Chapter 12

Kepler's Pecuniary Embarrassments--His Inquiries respecting the Law of Refraction--His Supplement to Vitellio--His Researches on Vision--His Treatise on Dioptrics--His Commentaries on Mars--He discovers that the orbit of Mars is an Ellipse, with the Sun in one focus--And extends this discovery to all the other Planets--He establishes the two first laws of Physical Astronomy--His Family Distresses--Death of his Wife--He is appointed Professor of Mathematics at Linz--His Method of Choosing a Second Wife--Her Character, as given by Himself--Origin of his Treatise on Gauging--He goes to Ratisbon to give his Opinion to the Diet on the change of Style--He refuses the Mathematical Chair at Bologna,