ABSTRACT
BY way of explanation of these pictures of snow on windows I must ask you to observe that Hhere are in the sky certain aerial causes why winds and whirlwinds occur; certain aqueous causes for clouds, rain, snow, hail, arcs, rainbows, and the like; and certain igneous causes of lightning, thunderbolts, sparkling effects, peals of thunder, and the various manifestations of fiery phenomena, including comets. To enable us to understand this more clearly Augustine states in his commentary on Genesis: This lower, murky air grows thick with a moist exhalation and, when it is disturbed, gives rise to winds; when more violently agitated, fires and peals of thunder; when compressed, mists; when condensed, rain; when frozen, snow; when turbulent, hail; and if expanded, clear weather. All this takes place at the secret commands of God, who governs all things from the highest to the lowest which He has created. So, with this air, which closely compasses the earth and is therefore allotted the lowest place, fine breaths are mingled in the form of vapour and interweave gentle breezes. When these are also made heavier by severe nights, they drip down clear dew; but if the cold is more powerful and the frost whiter, they themselves turn white. Moreover Aristotle says in the first book of his Meteorology that the first cause which sets in motion exhalations from the earth and water is the movement of the planets, that is of the sun and the rest, and when these vapours have risen up they produce phenomena in the sky. As the sun approaches or recedes from these materials of earth and water, it is the cause of their generation and corruption, that is of those qualities that are engendered in them. When the sun’s heat enters the earth, a moist or a dry vapour rises from it and then separates into its different components. If violent cold attaches to and affects the rising vapour, it turns into hoar-frost, which is vapour that has frozen in cool, cloudy regions, and from such vapour descend snow, frost, and hail. Snow comes from clouds in which cold and vapour have frozen together. Hail however falls from clouds a long way from the earth 1 and is formed from congealed rain, more by day than by night; it thaws 53into water much more quickly than snow does, so that when it falls at its heaviest it is called a storm.
Why winds and whirlwinds happen
Causes of celestial phenomena
Augustine on Genesis
Air
Reasons for phenomena are motions of planets
Hoar-frost
Snow
Hail
Storm
