This volume presents a critical edition of the final parts of Bate's Speculum. In these parts, which constitute the culmination of his Platonic-Aristotelian encyclopedia, Bate outlines a 'holistic' world-picture. Parts XX to XXII are devoted to the main topics of scholastic cosmology (the eternity of the world, the union of the heavenly bodies and their separate movers, the number and harmony of the spheres). Some original passages are of special interest for the history of medieval science: particularly Bate's theory of magnetism, his comments on observational errors, and his examination of diverse astronomical models. In Part XXIII, Bate concentrates on the metaphysical subject that stimulates his inquisitive mind to the extreme, that is, on the divine forms which move the spheres, and ultimately on 'the God of all gods'. In appendix a story about the apparition of a spirit has been added.

The Introduction comprises three sections: a summary of Bate's argument, an analysis of the chapter on magnetism, and a discussion of literary aspects of the Speculum.