been collected since, and in the hands of Mr. Buchan they have undergone such a careful and able analysis that the Challenger Reports charts may be taken as the best reliable representation of the winds, the temperatures, and the pressure in the lowest strata of the atmosphere, as well as the surest basis for further generalizations.[1] The theories which have been mentioned in the preceding pages give the grand lines of atmospheric circulation; on Buchan's maps we see how the grand lines are modified in the lowest strata by the distribution of land and sea, and the unequal heating or cooling of continents and oceans. The leading features indicated by theory are still maintained, and they become even still more apparent if we consult isobars traced for a certain height, like those of Teisserenc de Bort; but the immense plateaus of East Asia and North America act in winter as colossal refrigerators, where cold and heavy air accumulates, to flow down in all directions toward the lowlands. We see also how in July the air is heated in the lower lands of northwest India, in the corner between the Afghanistan and the Thibet plateau, how pressure is lowered there by the ascending current, and how winds blow toward this region of lowered pressure. We see more than that: on looking on the maps it strikes the eye how the moisture or the dryness of the climate is dependent upon the distribution of pressure, and how the dry anticyclonic winds make barren deserts of parts of North and South America, of Africa, and central Asia, and how they will continue to dry the lakes and the rivers of these regions and occasion total failures of crops so long as that distribution of pressure lasts on the globe, and man has not yet learned to eschew its effects by getting water from the depths of the earth. The life of the globe during the present period is written on these splendid charts.—Nineteenth Century.
- ↑ An excellent résumé of the whole work and its results in a popular form has been published by Buchan himself in the Proceedings of the Geographical Society, March, 1891.
made since, Mr. Buchan's isobars having been one of our best arguments to press the necessity of the leveling. But Mr. Buchan may not be aware that the leveling beyond the ninetieth degree of longitude is now considered by Russian geodesists as utterly unreliable; it is supposed to contain some substantial error, so that a new leveling between Krasnoyarsk and Lake Baikal is insisted upon. The incertitude in the isobars on an immense space in northeast Asia resulting from this cause may attain as much as one or, perhaps, even three tenths of an inch.
