Amongst all the writings of Christian ages in which matters such as we are now passing in review are described, there is one that stands out beyond all others as a masterpiece, and that is the magnificent poem of Dante, his _Divine Comedy_, wherein he described the infernal regions as they presented themselves to his lively and fertile imagination. We have in it a picture of mediaeval ideas, painted for us in indelible lines, before the remembrance of them was lost in the past. The poem is at once a tomb and a cradle--the tomb of a world that was passing, the cradle of the world that was to come: a portico between two temples, that of the past and that of the future. In it are deposited the traditions, the ideas, the sciences of the past, as the Egyptians deposited their kings and symbolic gods in the sepulchres of Thebes and Memphis. The future brings into it its aspirations and its germs enveloped in the swaddling clothes of a rising language and a splendid poetry--a mysterious infant that is nourished by the two teats of sacred tradition and profane fiction, Moses and St. Paul, Homer and Virgil. The theology of Dante, strictly orthodox, was that of St. Thomas and the other doctors of the Church. Natural philosophy, properly so called, was not yet in existence. In astronomy, Ptolemy reigned supreme, and in the explanation of celestial phenomena no one dreamt or dared to dream of departing in any way from the traditionally sacred system. In those days astronomy was indissolubly linked with a complete series of philosophical and theological ideas, and included the physics of the world, the science of life in every being, of their organisation, and the causes on which depended the aptitudes, inclinations, and even in part the actions, of men, the destinies of individuals, and the events of history. In this theological, astronomical, and terrestrial universe everything emanated from God; He had created everything, and the creation embraced two orders of beings, the immaterial and the corporeal. The pure spirits composed the nine choirs of the celestial hierarchy. Like so many circles, they were ranged round a fixed point, the Eternal Being, in an order determined by their relative perfection. First the seraphim, then the cherubim, and afterwards the simple angels. Those of the first circle received immediately from the central point the light and the virtue which they communicated to those of the second; and so on from circle to circle, like mirrors which reflect, with an ever-lessening light, the brilliancy of a single luminous point. The nine choirs, supported by Love, turned without ceasing round their centre in larger and larger circles according to their distance; and it was by their means that the motion and the divine inflatus was communicated to the material creation.