The first work, dedicated to King James I, represents Kepler's attempt at unifying geometry, astrology, music and astronomy into one harmonious system; it announces his discovery that the squares of the periods of the planets round the sun are proportioned to the cubes of the distances (Kepler's third law). The second work is a revised edition of Kepler's first scientific publication (Caspar 6); the Apologia concerns a polemic with Robert Fludd. The third work is the vindication of Maarten van den Hove's findings on the angular diameter of the sun, which had been vehemently criticized by Kepler in 1630.

PROVENANCE: Charles Fournerat (inscription; Paris sale October 1868); Dr. Ernst Weil (collation note).