Isidore’s physical universe[56] in its form is geocentric, and is bounded by a revolving sphere which he believed to be made of fire, and in which the stars are fixed. The question of the number of spheres he treats in an inconsistent way, sometimes speaking of seven concentric inner spheres, and sometimes of only one.[57] The relative size of sun, earth, and moon is accurately given—though, it appears, not without misgiving[58]—and also the cause of eclipses of both the sun and the moon. [56] For Isidore’s physical universe in general, see _Etym._ 3, 24–71; 13, 4–6; _De Natura Rerum_, 9–27. See pp. 142–154, 234, 243. [57] Isidore seems to have kept an open mind on the question of the number of the spheres. He says: _de numero eorum_ [_coelorum_] _nihil sibi praesumat humana temeritas_. _D. N. R._, 13, 1. [58] See 2, 24, 2 (p. 116). The subject of greatest interest in this connection is, of course, the question whether or not Isidore believed in the sphericity of the earth. It is maintained by some authorities that this notion was not lost at any time during the middle ages. Isidore certainly believed that the heavens constituted a sphere or spheres, and that the sun and moon revolved in circles around the earth. He states the theory of the zones correctly in two passages,[59] applying it, however, not to the spherical earth but to the sphere of the heavens. On the other hand, he frequently gives expression to notions belonging to a primitive cosmology.[60] The suspicion is aroused, therefore, that when he was stating astronomical ideas, he was usually simply copying what perhaps he did not understand. A passage that seems to settle the matter is found in _De Natura Rerum_. It shows that the fact that he could state such a theory as that of the zones correctly, is no proof that he understood its application to the earth. A translation of the passage follows: [59] 3, 44; 13, 6. See p. 146. [60] See Appendix I.