Page:Popular Science Monthly Volume 11.djvu/405

Rh Forests produce rain. Under the influence of vertical sun-rays trees exhale the aqueous vapors which their leaves have absorbed from the atmosphere, and in contact with the night-air or any stray current of lower temperature, these vapors discharge rain-showers even in midsummer, and at a great distance from the sea.

By moistening the air woodlands also moderate the extremes of heat and cold. It is seen on the sea-shore how beneficently humidity operates in allaying the severity of winter, and in summer the evaporation of dew and rain gives us cool breezes when they are most needed. By the extirpation of forests the climate of the entire Orbis Romanus has been changed from the summer temperature of West Virginia to the furnace-heat of New Mexico and Arizona.

Besides this, the forest by shade in summer and fuel in winter protects us directly against the vicissitudes of temperature, and at the foot of high mountains interposes a mechanical barrier between the valleys and avalanches in the north, and floods in the south. The water-torrents, which not only flood and damage the lowlands, but carry their fertile soil away, are imbibed or detained by extensive forests. Joseph II. of Austria was right to attach heavy penalties to the destruction of the "Bannwälder," the woods on the Alpine slopes, that protect the valleys from avalanches, and to propose that in wars, even à l'outrance, the trees of a country should be spared by international agreement.

Our woods are also the home and shelter of those best friends of man, the insectivorous birds. A country destitute of trees is avoided by birds, and left to the ravages of locusts and other insects, which, as we saw on our own continent, always attack the barren and naked districts. Our locust-swarms devastated the "Great West," i. e., the treeless expanse between the Mississippi and the Rocky Mountains, but spared the woodlands of the Alleghanies and the timber-regions of the Pacific slope.

The exhilarating influence of a woodland excursion is not altogether due to scenic effects and imagination. Forests exhale oxygen, the life-air of flames and animal lungs, and absorb or neutralize a variety of noxious gases. Scirrhous affections of the skin and other diseases disappear under the disinfecting influence of forest-air. Dr. Brehm observes that ophthalmia and leprosy, which have become hereditary diseases, not only in the valley of the Nile, but also on the table-lands of Barca and Tripoli, are utterly unknown in the well-timbered valley of Abyssinia, though the Abyssinians live more than a hundred geographical miles nearer to the equator than their afflicted neighbors.

The traditions of the "blessed islands of the West," the "Garden of the Hesperides," probably referred to Madeira and the Cape-Verde Archipelago, which, according to De Gama's description, must have come nearer to our idea of terrestrial paradise than any other region