In her _Causae et curae_, on the one hand, and in her _Scivias_ and _Liber divinorum operum_, on the other, Hildegard of Bingen makes contradictory statements in regard to the position of the earth in relation to the heavenly spheres. Scientific consistency was not, perhaps, the ascetic abbess’s strongest quality, and too much emphasis should not be laid upon contradictions found in the writings of one who believed herself to be favored by special divine revelations. The passage in the _Causae et curae_, however, diverges so widely from current medieval opinion that it is worth translating. “The earth,” writes Hildegard, “is of moderate size and is near the base of the firmament, because if it were in the center of the firmament, then it would have to be larger; and even so it would easily fall and be shattered to pieces, had it the same expanse of air beneath that there is above.”[659] On the contrary, in her _Liber divinorum operum_ she tells how she saw in a vision the universe as a wheel[660] and that “in the midst of the air the earth was placed in such a way that the air measured an equal distance above the earth, below the earth, and on either side of the earth.”[661] SHAPE OF THE EARTH Most writers of the Crusading age thought the earth also was a sphere, though there was less unanimity in this belief. The _De imagine mundi_ calls it a sphere, whence comes the term _orbis_.[662] William of Conches[663] furnishes us with the Aristotelian proofs of sphericity. If the earth is flat, he says, it would be day at the same time in the farthest east as in the farthest west. Certain stars are visible in one latitude that cannot be seen in another, and this would not be the case if there were no curvature from north to south.[664] John of Holywood, following Al-Farghānī, gave two proofs that the earth is round and two that the water is round.[665] That there exists a swelling or curvature of the earth (_tumor terrae_), he says, is shown by the difference in the time of eclipses between places in the east and west as well as by differences in the visibility of stars.[666] The curvature of water surfaces is demonstrated by the fact that a person standing at the foot of a mast is frequently unable to see objects visible to somebody at the masthead. Furthermore, since water is a homogeneous body, all parts of it must partake of the nature of the whole. Therefore it follows that because a drop is round, the mass of the waters of the earth must also be spherical.[667] Gervase of Tilbury has been accused of believing that the earth is square, though the evidence in the text of the _Otia imperialia_ on which this accusation is based is very slender; and other texts would seem to support the opposite contention, that he accepted the theory of sphericity.[668]