With the vanishing of the ice-sheets and the setting in of the mild climate of the Maritime phase the Neolithic culture spread rapidly to Europe, and by 2000 B.C. even the Baltic regions were well inhabited, and it is probable that the Aryan race was developing in the Russian steppes. About this time Anau was abandoned owing to increasing aridity. With the coming of the Bronze Age in western Europe, about 1800 B.C., however, the climate again became colder and rainier, corresponding to the Peat-bog phase or “Classical” rainfall maximum, the deterioration culminating in the Early Iron Age. This period was marked by a great southward spread of the Aryan peoples, and ushered in the Heroic Age of Greece. The races of the Mediterranean, as we have seen, continued to thrive throughout this rainy period, and their power did not diminish until its close, about A.D. 400. This downfall was accelerated if not caused by the pressure of nomad peoples driven out of Asia by the increasing drought. These Asiatic migrations included the great marches of the Tartar hordes and, aided by religious enthusiasm, the conquests of the Moslems. The early Middle Ages, after the downfall of Rome, appear to have been characterized by a dry warm climate. This was the age of the Vikings, when the Norse races rose to dominance in western Europe, finally invading and occupying large areas of France and Britain, and even extending their power to Sicily. With the increasing cold and wet of the “Mediæval” rainfall maximum came a final burst of Norse migration, which left the homeland poor and scantily populated, and the centre of activity and progress lay once again with the Mediterranean peoples, and especially with Italy and Spain. The Tartar invasions ceased, and against the increasing power of Europe the Moslem wave broke and receded. At the close of this rainy period political dominance again moved north. From that time the fluctuations of climate have been of minor importance, and correspondingly there have been no great shiftings of political power from latitude to latitude. BIBLIOGRAPHY. Tyler, J. M. “The New Stone Age in Northern Europe.” London, 1921. Huntington, Ellsworth, “World Power and Evolution.” New Haven, 1919. Haddon, A. C., “The wanderings of peoples.” Cambridge University Press, 1919. APPENDIX THE FACTORS OF TEMPERATURE To calculate the probable temperature of January or July at any point, the following procedure should be adopted: