(C) CLIMATE, VEGETATION

(a) Climate of the Alps

It is well known that as we rise from the sea-level into the upper region of the atmosphere the temperature decrease. The effect of mountain chains on prevailing winds is to carry warm air, belonging to the lower region into an upper zone, where it expands in volume at the cost of a proportionate loss of heat, often accompanied by the precipitation of moisture in the form of snow or rain. The position of the Laps about the centre of the European continent has profoundly modified the climate of all the surrounding regions. The accumulation of Vast masses of snow, which have gradually been converted into permanent glaciers, maintains a gradation of very different climates within the narrow space that intervenes between the foot of the mountains and their upper ridges; it cools the breezes that are wafted to the plains on either side, but its most important function is to regulate the water supply of that large region which is traversed by the streams of the Alps. Nearly all the moisture that is precipitated during six of seven month is stored up in the form of snow, and gradually diffused in the curse of the succeeding summer; and even in the hottest and driest seasons the reserves accumulated during a long preceding period of years in the form of glaciers are available to maintain the regular flow of the greater streams. Nor is this all; the lakes that fill several of the main valleys on the southern side of the Alps are somewhat above the level of the plains of Lombardy and Venetia, and afford an inexhaustible supply, which, from a remote period, has been used for the system of irrigation to which they owe their proverbial fertility.





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