[69] For a clear account of the theory of the four elements in medieval thought see Les Quatre Elements, J. Leminne in Mémoires couronées par l’Académie Royale de Belgique, v. 65, Bruxelles, 1903.
[70] Etym., 13, 3. Cf. D. N. R., 11.
[71] The theory of atoms is also stated by Isidore. See [p. 235]. It is not used, however, and is not fully stated. The part played in the theory by atoms of different sizes is not mentioned, and although “the void” is mentioned, its importance is not brought out.
[72] See Art. “Chemistry,” Encyclopedia Britannica, 11th edition.
[73] Etym., 13, 5, 1.
[74] Diff., 1, 82.
[75] De Ordine Creat. Liber, 4, 5–6. Cf. D. N. R., 11. The problem of “the waters above the firmament,” which occupied the minds of the church fathers so much, and which is at variance with the cosmological side of the theory of the four elements, Isidore seems inclined to settle by regarding it as a miracle. Cf. D. N. R., 14.
[76] In the De Natura Rerum and the De Ordine Creaturarum, as well as in Books XIII-XIV of the Etymologies, Isidore follows the order of the four elements in describing the universe. His fidelity to this order, as well as the variations of emphasis and of minor treatment which he introduced into it, are of interest. These may be exhibited in parallel form as follows:
| Etymologies Books xiii and xiv | De Natura Rerum | De Ordine Creaturarum | |
|---|---|---|---|
| xiii, chaps. 4–6 | chaps. 9–27 | 4–6 | |
| Fire (the heavens) | Astronomy | Astronomy, fuller | Astronomy, briefer, with an account of the angels, the inhabitants of the element of fire |
| xiii, 7–12 | 28–39 | 7–8 | |
| Air | The atmosphere and meteorological phenomena | The same, fuller | The same, briefer, with an account of demons, the inhabitants of the air |
| xiii, 12–22 | 40–44 | 9 | |
| Water | A description of water with a geography of the water surface of the earth | The same in very much abbreviated form | The same, briefer, without the geography |
| xiv, 1–9 | 45–48 | 10–15 | |
| Earth | A description of the dry land with a geography of the land surface of the earth | The same in very much abbreviated form | The same, briefer than in De Natura Rerum, with an account of men as the 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.