DRYING UP SLOWLY.

Inangahua Times, Volume IV, Issue 15, 14 May 1877, Page 2

DRYING UP SLOWLY.

Professor J- D. Whitney, in the last number of the American Naturalist, shows that the popular notion that the destruction of forests much affects the quantity of rain, is erroneous. The records which bare been kept of the height of waters in the Danube, Elbe, Rhine and other great European streams, show that they are carrying a less amount of Water than formerly. The great lakes of Central Asia are now dried up, and the Humboldt country, once a rast lake, is now a dry basin. Still in a qualified way it is true that forests arrest evaporation,- cool the ground by protecting it from the more direct rays of the sun, and in that way secure to a country a far greater degree of

moisture than it otherwise would hare. Bat the denudation of forests does not iccount for the drying up of great lakes. Professor Whitney ascribes this change to 3olar causes, and hts view is set forth in the following summary j— "The sun's heat is notoriously the source of all climates, and changes in the amount of heat radiated from the son are now regarded as causing the changes in terrestrial weather. It is therefore reason* able to ascribe oar drying-ap» since it requires ages for its completion, to a change in the solar cause requring also % long cycle for its fulfilment, provided that astronomy gives us proof of any such change. And astronomy tells us of two such cycles ; one in the obliquity of the elliptic, and one in the perihelion distance of the earth from the sun, both cycles being resnlts of perturbations of the earth s orbit. The effect of the second of these cycles is too abstruse to explain here ; the first is simpler. As the angle between the plane of the earth's euqator and that of her orbit dimishes, the limits of the torrid zone also diminish, inasmuch as that zone is bounded by the tropics which are determined by the angle in question. The region, then, oyer which the sun is occassional'y vertical is being narrowed. An obvious result of this nar* rowing would seem to be an intensification of the equatorial phenomena of tradeW'Dils, beat and rainfall within the torrid zone, and a corresponding loss of heat and of precipitation in the extra-tropical zones.