Note 686 — Chapter VI · COSMOGONY, COSMOLOGY, AND COSMOGRAPHY

“Item si intelligatur superficies plana super centrum terrae dividens eam in duo aequalia, et per consequens ipsum firmamentum, oculus igitur existens in centro terrae videret medietatem firmamenti; idemque existens in superficie terrae videret eandem medietatem. Ex his colligitur quod insensibilis est quantitas terrae quae est a superficie ad centrum et per consequens quantitas totius terrae insensibilis est respectu firmamenti” (loc. cit.).

John of Holywood’s argument is here closely related to that employed 427by him to prove that the earth must be in the center of the universe as set forth above, p. 422, note 81. It would seem probable that by “an eye stationed in the center of the earth” he means an eye on a line between the center of the earth and the medietas firmamenti, and by “the same (eye) stationed on the surface of the earth” he means on the surface at a point where a line at right angles to the line from the center of the earth to the medietas firmamenti cuts the surface of the earth. Referring, then, to Figure 10, p. 422, above, let us assume that line E-E′ represents the plane through the medietas firmamenti and the center of the earth (C). When the earth is at the center of the universe line C-N′ will represent the line drawn at right angles to this plane. With a universe of infinite dimensions obviously N′-E and N′-E′ would be parallel to E-E′, and the medietas firmamenti would be visible from N′. John assumes that the universe is so large in relation to the earth that the area around N′ whence E-E′ would be invisible is negligible.