Note 743 — Chapter VII · THE ATMOSPHERE
Reading edition
The origin of this story has not been traced by the present writer. It would certainly seem to be based on some actual knowledge of the physiological effects of lower air pressure at great heights.
According to Benini (Origine del Monte del Purgatorio, 1917, 432p. 1085) Dante (Purgatorio, XXVIII, 103–112; see also Inferno, IV, 26–28, 149–150) held that the Mount of Purgatory reaches above the lower levels of the atmosphere, which are corrupted by the earth and where winds, clouds, rain, hail, and rainbows are to be found, into a realm of motionless air. The very summit of the mountain where the Terrestrial Paradise is situated is in a belt of air which moves from east to west with the motion of the ninth sphere.