Page:Popular Science Monthly Volume 82.djvu/333

Rh water supply for the garrison, this water being contributed partly by "slight showers" and partly by the "steady dripping" just referred to. "Every exposed object," says Professor Abbe, "contributes its drip." Another case, described by William L. Hall, in the Hawaiian Islands, is that of the collection of the drip from the trees in a region of heavy fog (? cloud) in troughs for the use of cattle. In this locality deforestation would, it is stated, "reduce the productiveness of the plantations, if not ruin them entirely."

The present writer has several times, during fogs, noted the dripping of water from the wires above the sidewalks in his own city. The sidewalks being dry at the time, the drops from each wire made a wet line on the pavements. Again, when steaming through the thick fogs on the Grand Banks of Newfoundland, many of us have seen real, though gentle, showers of rain falling from the wet rigging on to the dry decks.

In winter, when the moisture freezes on the trees, the branches and twigs may become heavily covered with "frost." Fischbach has noted the fact that in winters of deficient snowfall in the Black Forest, he has several times observed that the frost shaken off of the trees by the wind has made possible the use of sledges for transporting wood. In one single European case, reported by Wilhelm, the amount of "rainfall" resulting from the occurrence of such a frost deposit on trees was not far below.05 inch.

In this mechanical collection of water particles by a forest, we seem to have a really effective means of increasing the total fall of rain. It is easy to see that if such favorable conditions are often repeated, and where the trees are tall and have many branches, the surface of the ground beneath the forest may easily receive a not inconsiderable supply of moisture. Such action on the part of forests is further aided by the fact that fogs often seem to last longer among trees. Nevertheless, we should remember (1) that the conditions favorable to this particular forest influence are found only locally, especially on forested mountain slopes and tops; (2) that the increase in the fall of rain is limited to the area covered by the forest itself, and is, therefore, not upon soil used for agriculture; and (3) that in the European observations, above referred to, this particular action of forests was at work, as well as all other forest influences, yet the results were, as has been seen, uncertain.

There has been a widespread impression in parts of Europe that hailstorms avoid forests, and that forests serve to break up and to weaken other storms. The evidence on the question of hailstorms is conflicting, but we may say that the popular impression can be explained on the ground that hail naturally does more damage to tender crops