THE GEOGRAPHIC BASIS OF HISTORY 365
Chinese Turkestan, where parching winds abound, are nervous, emotional, and uncontrolled. As a matter of fact, they are not so nervous as might be expected ; but they are certainly highly emotional, and very lacking in self-control. This, it may be, explains why the Persians are so prone to lying. The habit of telling the truth can be acquired only by long practice, by a continual exercise of the will in opposition to the suggestions of fear, greed, or the other feelings. So after all, perhaps it is " a matter of climate." And the obvious corollary is that during the last two thousand years a change in the climate of Persia may have contributed materially to a change in the character of the people, as Malcolm's story suggests.
Before we can properly estimate the influence of climatic changes upon history, it is necessary to investigate the types of change and the reasons for believing that climate varies uniformly over very wide areas.
Hitherto scientists have recognized two chief types of climatic change. The first is that of the Glacial Period, during which great fluctuations took place simultaneously, as it is believed, over the whole world, or at least throughout the northern hemisphere. The other is not so well known, as it was only discovered about 1890. Bruckner, seconded by . Clough and others, has shown good reason for believing that once in thirty-six years, on an average, the whole world passes through what may be called a climatic cycle. During a cycle there are two extremes, at one of which the climate of continental regions for a series of years is unusually cool and rainy, with a low barometric pressure and relatively frequent storms; while at the other it is comparatively warm and dry,
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