f. 1r-v Book One: The Sphere of the World, that is, cosmography, comprehending summarily, the whole structure of the World, I mean, a description of the heavenly and elemental region. Chapter 1. Concerning the definition of the World and of its more significant parts. Since it is the part of our plan to write a treatise concerning the structure of the World and its motion, and what things in these lower [regions] are derived from that [motion], it seems good in the first instance that a definition of the World should be offered. {Definition of the World.} The World, therefore, is the name for the whole and complete arrangement of all things adorned with every kind and species of bodies that nature has been able to bring forth. {Cosmography.} Whence, it is called by the Greeks, cosmos, and the discipline that treats of the World is correspondingly called cosmography (it is for the present undertaking to deal with this). For cosmography is a description of the structure of the World, general and not displeasing, including the first part of astronomy and also geography, that is, an account of heaven and Earth. {Two very important parts of the World.} Moreover, the entire structure, or composition, of the World, is clearly shown, both by sense and reason, to be made whole by twin and indeed by particular and very important parts: namely, the elemental region being always occupied by generations and corruptions, and the surrounding heavenly fabric which is altogether devoid of alteration and it is providentially adorned with shining stars both fixed and wandering by the highest creator of things. {The Elements [are a] material cause, but the sky is the maker of all that generate.} The Elements, mixed in a diverse way and moreover reciprocally in proportion [to each other], are, as it were, the material cause, but the heaven by its power and continual motion, which is diffused by mediating light and motion, is the formal and specific cause of all things which are generated in these inferior [regions], and take their life from heaven, but the sustenance from the Elements. Now behold this figure of these regions. [Figure captions: Celestial region; Elemental region.]