The first edition in English of Galileo's Dialog and of his Letter to the Archduchess of Tuscany on the relation of science and theology, together with other important texts on the subject, by Johannes Kepler and others. The Dialogo, Galileo's most famous work and of seminal importance in establishing the heliocentric theory of the solar system, comprises the major portion of the volume, the first 424 pages. This edition was first issued in 1661 as Vol. I of a projected two-volume work. But nearly all copies of the 1665 second volume were destroyed in the Great Fire of London (only one volume of the second part of Vol. II is known, and only ten copies of the first part of Vol. II). The sheets of Vol. I were reissued in 1667, with a new title-page and contents leaf (omitting reference to those works that were in Vol. II). This second issue is much rarer than the first issue - WorldCat lists only those copies at the University of Oklahoma and the American Philosophical Society, and ESTC adds the copies at Marsh's Library and Oxford University Corpus Christi College. We found only three auction records for the 1667 issue, since 1965. Bound without a half-title (we are unable to determine whether one was issued with this issue). Wing S517A.