Page:Popular Science Monthly Volume 72.djvu/496

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MONG the inorganic factors by which the fitness of the earth for human occupation is most profoundly influenced, two of the chief are climate, on the one hand, and telluric activity on the other. To climate we owe much of the nature and depth of the soil upon which all life depends; it determines the character of vegetation, and makes possible the vast commerce which consists of the exchange of the vegetable products of one land for the commodities of another; it causes men to engage in different occupations, some, for instance, raising rice in the warm plain of Egypt, and others leading the life of the lumberman or trapper in the cold woods of Canada; and finally climate exerts a profound influence upon human temperament, the inhabitants of the torrid zone, as is generally recognized, being notably less energetic than those of temperate regions. Telluric activity, manifested in movements of the earth's crust, past and present, is equally important, though its effects are not so immediately visible. The ravages of earthquakes and volcanoes, great as they are, fade into insignificance when compared with the stupendous results which have followed from the upheaval of continents and folding of thick strata of solid rock. If telluric processes had not throughout the ages again and again upheaved the crust of the earth, the climatic forces of weathering and erosion would long ago have reduced the original continents to featureless plains of small extent compared with the present great areas of land. There would be no mountains full of minerals, and the use of metals would probably be unknown because none would have been discovered by reason of the enormous depth of soil which would cover the country.

In the study of climate and of telluric activity, attention has till recently been concentrated upon the earth. Within a few years, however, scientists have begun to turn to the sun to see if its changes are in any way connected with changes of climate or with the occurrence of earthquakes and volcanic eruptions. At first the results were negative. Of late, however, students of solar physics have shown that there are now in progress fluctuations of climate which appear to be coincident with variations in the activity of the sun as evinced by the occurrence of sunspots; and the investigations of Jensen, as I shall