They descend a cliff over loose stones which roll under the unaccustomed weight of Dante’s living feet. Virgil tells him that both here and elsewhere in Hell the ancient rocks were riven by an earthquake which immediately preceded the triumphant descent of Christ after His crucifixion. So mighty was the shock that he thought the universe was dissolving into chaos by the force of love, as Empedocles had said must happen periodically. At the base of the cliff they cross the river Phlegethon, then pass through the wood of the Harpies, and walk along the stone banks of a conduit which afterwards falls with thunderous roar down a steep precipice. On the burning sand through which the conduit runs, Dante sees Brunetto Latini, and tells him that it was only yesterday that he escaped from the Forest. The monster Geryon carries them down the precipice, and they reach the ten Pits of Malebolge, which like so many moats surround the central Depth. When looking down upon the astrologers in the fourth Pit, Virgil again hastens Dante on, telling him that now Cain and the thorns—by which he means the moon, alluding to the legend[457]—is on the boundary of the two hemispheres, and already touching the waves below Seville. The two hemispheres are those of the habitable earth whose centre is Jerusalem, and the uninhabitable with Purgatory at its centre: the moon, therefore, is just setting as seen from Jerusalem, and in the Inferno the time is Jerusalem time. It is here that Virgil adds, “And yesternight the moon was full:” did we not know this, the fact that she was setting would give no clue to the time. When full, she set as the sun rose, that was at 6 a.m.; now, therefore, she is setting after sunrise, between six and seven in the morning;[458] and this is how Virgil tells Dante, without mentioning the sun, that a new day has begun. ------------------------------------------------------------------------ [457] _Cf. Par._ ii. 48-51. [458] The retardation is not likely to be more than the average of 50 minutes, and may be less, because the moon is in Libra, and therefore going south. This tends to diminish the interval between one moonset and the next in the northern hemisphere, just as the days get shorter when the sun goes south in autumn. ------------------------------------------------------------------------