Thunder is rare both in winter and in summer[2], but from different causes; the air, which is condensed in the winter, is made still more dense by a thicker covering of clouds, while the exhalations from the earth, being all of them rigid and frozen, extinguish whatever fiery vapour it may receive. It is this cause which exempts Scythia and the cold districts round it from thunder. On the other hand, the excessive heat exempts Egypt; the warm and dry vapours of the earth being very seldom condensed, and that only into light clouds. But, in the spring and autumn, thunder is more frequent, the causes which produce summer and winter being, in each season, less efficient. From this cause thunder is more frequent in Italy, the air being more easily set in motion, in consequence of a milder winter and a showery summer, so that it may be said to be always spring or autumn. Also in those parts of Italy which recede from the north and lie towards the south, as in the district round our city, and in Campania, it lightens equally both in winter and in summer, which is not the case in other situations.