Fire Astronomy Astronomy, fuller Astronomy, briefer, (the with an account of heavens) the angels, the inhabitants of the element of fire xiii, 7–12 28–39 7–8 Air The atmosphere and The same, fuller The same, briefer, meteorological with an account of phenomena demons, the inhabitants of the air xiii, 12–22 40–44 9 Water A description of The same in very The same, briefer, water with a much abbreviated without the geography form geography of the water surface of the earth xiv, 1–9 45–48 10–15 Earth A description of the The same in very The same, briefer than dry land with a much abbreviated in _De Natura Rerum_, geography of the form with an account land surface of of men as the the earth inhabitants of this element, their nature and future life This table indicates the great stress Isidore laid upon the cosmological side of the theory of the four elements, as well as his tendency to use his large general ideas in relating the individual branches of knowledge. Here astronomy, meteorology, and geography are thus grouped together, and angelology is put into relation with astronomy and demonology with meteorology. [77] _Etym._, 13, 3, 3, and 8, 11, 17. The theory of the four elements was fertile in every branch of the natural science of medieval times. Isidore uses it, for example, to explain the physical constitution of man: