Page:Popular Science Monthly Volume 69.djvu/467

Rh earlier than during the preceding century, but three days later than during the second century preceding. At the present time, the average date of the grape harvest in Aubonne is exactly the same as at the close of the sixteenth century. After a careful study of the conditions of the date tree, from the fourth century, B. C., Eginitis concludes that the climate of the eastern portion of the Mediterranean basin has not changed appreciably during twenty-three centuries. In China, a comparison of the ancient and present-day conditions of cultivation, of silk production, and of bird migrations, has led Biot to a similar conclusion. In some cases, the reported cultivation of cereals, or other soil products, in certain at present unfavorable climates has been shown to be purely a myth; as in the case of a supposed extended cereal cultivation in Iceland in former times.

Secondly, a good many of the reports by explorers from little-known regions are contradictory. Thus Lake Aral, which was diminishing in area for many years, is recently reported by Berg as increasing. Lake Balkash, which was rapidly drying up, has also begun to fill again. Partly submerged trees are noted as having been seen by Berg, who in June, 1902, found the lake waters quite fresh. As the lake has no outlet, this is an interesting fact. In Africa, Lake Victoria which, it was generally agreed, was sinking in the period 1878-1892, has since shown a tendency to rise. Lake Bukwa, east of Tanganyika, has risen within the last few years. Reports that the Sea of Azov is drying up have been explained as due to a silting up of a lake. Lake Chad is very probably subject to oscillations, sometimes spreading beyond its usual limits as the result of several years of heavy rainfall. Such diverse reports show the need of caution in jumping at conclusions of climatic change. An increased use of water for irrigation may cause the level of water in a lake to fall, as has been the case to some extent in Great Salt Lake. Periodic oscillations, giving higher and then lower water, do not indicate progressive change in one direction. Many writers have thus seen a law in what was really a chance coincidence. Partsch believes that the ancient settlements on the interior lakes of northern Africa show that these lakes contained no more water formerly than they do now. Some have claimed that the supposed desiccation of the climate of northern Africa resulted from deforestation, but no certain evidence exists of the presence or destruction of such forests, and if deforestation did take place, no considerable change of climate could have resulted.

Thirdly, where a progressive desiccation seems to have taken place, the question should be asked, is less rain actually falling, or have the inhabitants less capacity, less energy, less ability than formerly? Is the change from a once cultivated area to a barren expanse the result of decreasing rainfall, or of the emigration of the former inhabitants