Theodoric of Chartres gives a clear statement[749] of the theory of evaporation, condensation, and precipitation in terms that sound almost modern. Heat, he says, causes water to ascend into the atmosphere in minute drops which form clouds. If the heat increases, these droplets turn to pure air; if it diminishes, they coalesce into rain. The most minute drops are constricted by a cold wind into snow; when the drops are large they are converted into hail by the same agency.[750] Topographic influences on precipitation were partially understood by Giraldus Cambrensis, who believed that the influence of land—particularly hilly land—frequently tends to change the vapors of the air into mists and clouds, or rain and snow.[751] In the seas off Ireland, for instance, water is attracted into the atmosphere in immense quantities; the temperature being equable, the water is neither consumed by an excess of heat nor turned to snow by an excess of cold but is altered into rain, a process greatly facilitated by the presence of many mountains in Ireland. FLOODS; THE DELUGE An excess of rainfall results in floods. William of Conches believed that under normal conditions the warmth of summer counteracts the excessive dampness of winter but that a long series of cool, damp summers will end in floods and, conversely, a series of hot, dry summers will end in droughts. But, however many local floods there may be, only one _diluvium_, or deluge, is possible.[752] Whence came the waters of the Deluge? This was a question which puzzled some of the commentators on Scripture during the Middle Ages. Adelard, though he did not believe it himself, cited a theory that the purpose of the waters above the firmament was to furnish these waters.[753] Peter Comestor,[754] followed by Gervase of Tilbury,[755] said that they came partly from the bowels of the earth and partly from the air above and that they rose higher than the tops of the mountains of today,[756] to the level to which the vapors of burnt offerings ascend. Gervase also spoke of a curious theory that there may have been no rain in Paradise nor anywhere on the earth until the time of the Deluge.[757] The vegetation in the Garden was watered in these early days by the heavenly dew. The argument that no rain fell until the Deluge was based, he said, on the words of God to Noah: “I will no more curse the earth for the sake of men; ... seedtime and harvest, cold and heat, summer and winter, night and day shall not cease” (Gen. viii, 21–22). Gervase adds: “Perhaps the four seasons were not yet fully distinguished one from the other, since not until the time of the Deluge were the waters gathered into clouds.”[758] According to the _Liber divinorum operum_ of Hildegard the temperature was far hotter before the Deluge than it has been since, and “the men of that time possessed great bodily strength in order that they might endure this heat. The Deluge reduced the