This Aristotelio-Ptolemaic system[2] formed a coherent framework for biblical world-notions. Here too, earth stands still while sun and stars revolve; here, too, the seat of Deity is the highest heaven. This was an universe where men could feel their feet on firm ground; their minds found rest in those simple and definite notions which make religious conceptions easy to understand and accept; their imaginations were not yet disturbed and disquieted by thoughts of space and time without end and without beginning. AQUINAS.--Such was the "world of nature," the theatre for that "world of grace" which Revelation spoke of, and which led eventually to the eternal "world of glory" in which the faithful should have their portion. _Natura_, _gratia_, _gloria_ was the ascending series (like another set of celestial spheres), and the whole economy was elaborated into a logical system, known to the historians of thought as Scholasticism: a philosophy which found its most perfect and memorable expression in Thomas Aquinas (1227-74), the _doctor angelicus_ of Catholic theology, canonised less than fifty years after his death. The _Summa Philosophica_, where Aquinas deals with the rational foundations of a Christian Theism, and the _Summa Theologica_, where he erects his elaborate structure of theology and ethics, together constitute "one of the most magnificent monuments of the human intellect, dwarfing all other bodies of theology into insignificance."[3] In him the erudition of an epoch found its spokesman; he was the personification of an intellectual ideal. To his contemporaries he stood beyond the range of criticism. In the _Paradiso_ (x.8.2) it is St. Thomas who speaks in heaven. Nevertheless, the Scholastic world-scheme, though based on "the evidence of the senses, the investigations of antiquity, and the authority of the Church," and though Aquinas had set the seal of finality upon it, was destined to gradual discredit and ultimate extinction. DISINTEGRATION BEGINS.--It was open to attack on two sides. _Either_ observations or calculations might be brought forward, conflicting with it, or making another conception possible or probable: _Or_ the validity of conventional ideas of space might be disputed. The latter type of criticism was the first to occur. Nicholas Cusanus (1401-1464), an inhabitant of the Low Countries, subsequently bishop and cardinal, developed unconventional notions about Space. He suggested that wherever man finds himself--on earth, sun, or star--he will always regard himself as standing at the centre of existence. There is, in fact, no point in the universe which might not appropriately be called its centre, and to say that the earth stands at the centre is only (what we should now call it) an anthropomorphism. So much for _place_; and similarly with _motion_. Here, too, there is no absolute standard to apply: motion may exist, but be unnoticed if there be no spot at absolute rest from which to take bearings.