Page:Popular Science Monthly Volume 69.djvu/463

Rh indicates a gradual desiccation from early historical times down to the present day. His study of climatic changes in that region is one of the most thorough ever made, for the evidence of archeology, of tradition, of history and of physiography has been carefully matched and found to accord in a very striking manner. Huntington has found evidence of the abandonment of successive village sites as the inhabitants moved further upstream in search of more water. Patches of dead jungle show that vegetation once flourished where aridity now renders plant growth impossible.

In northern Africa certain ancient historical records have been taken by different writers to indicate a general decrease of rainfall during the last 3,000 or more years, the remains of cities and the ruins of irrigating works pointing to a larger population and a greater water supply formerly than at present. The presence of certain animals, now no longer found there, is implied by ancient records, and from this fact also a change of climate is inferred. In his crossing of the Sahara between Algeria and the Niger, Gautier found evidence of a former large population. A gradual desiccation of the region is, therefore, believed to have taken place, but to-day the equatorial rain belt seems to be again advancing farther north, giving an increased rainfall. Gautier divides the history here into three periods, (1) dense population, (2) aridity, and (3) the present change to a steppe character.

Farther south, several lakes have been reported as decreasing in size, e. g., Chad, Ngami and Victoria; and wells and springs as running dry. In the Lake Chad district, Chevalier reports the discovery of vegetable and animal remains which indicate an invasion of the Sudan by a Saharan climate. Neolithic relics indicate the former presence there of prosperous communities. Again, to note another instance, it is often held that a steady decrease in rainfall has taken place over Greece, Syria and other eastern Mediterranean lands, resulting in a gradual and inevitable deterioration and decay of their people. These examples might be multiplied, for reports of climatic changes of one kind or another are numerous from many parts of the globe.

What Meteorological Records show.—As concerns the popular impression regarding change of climate, it is clear at the start that no definite answer can be given on the basis of tradition, or of general impression, or even of the memory of the 'oldest inhabitant.' Human memories are very unreliable things, and there are many reasons for their being particularly untrustworthy in matters of this kind. The only answer of real value must be based on what the instrumental records of temperature, and of rain and snowfall show. Accurate instruments, properly exposed, and carefully read, do not lie; do not