Page:Popular Science Monthly Volume 36.djvu/552

536 have any appreciable, to say nothing of a considerable, effect on the climate. Even in irrigated countries only a barely perceptible increase in the rainfall has been discovered. In Spain, France, and Italy, irrigation is now not only required for farming, but it is more widely practiced than ever before; yet, if the "rain-belt" theory were correct, these countries would long ago have had sufficient precipitation for successful agriculture. There is scarcely any rainfall in the valley of the Nile to-day, after centuries of cultivation and of annual floods.

Our "plains," or arid region, lie east of the Rocky Mountains, and are at least four hundred miles across. Although the precipitation gradually decreases as one proceeds westward from the Missouri River, it is difficult to fix an isohyetal line. But the line is somewhere between one hundred and two hundred miles west of the Missouri, as the flora clearly shows. It seems to have been taken for granted that the plains were treeless and well-nigh grassless because of lack of rain. Whether the absence of trees is ascribable to the pulverulence of their soil, or the germless lacustrine deposit which covers them, or the excess of moisture, or the fires of the Indians, it is clear that it is not due to rainlessness, because the dry hill-tops in the midst of the arid region have some trees. In other words, there is no evidence whatever that the precipitation on the plains to-day is any greater than it was fifty or one hundred years ago; and there is every reason to believe that it is less.

But, it is said, the observations west of the Missouri show a material increase in the rainfall. This is not true. In the reports of the Kansas State University and the Kansas State Agricultural College we learn that the rainfall for the ten years from 1879 to 1888 is not so great as that of the previous decade. One authority on the subject has recently taken, among other series, the observations at Fort Leavenworth from 1837 to 1883, and, testing by the proper mathematical processes their variabilities and probabilities, demonstrates that there is no indication whatever of permanent climatic change. Yet Fort Leavenworth is one hundred and fifty miles east of the eastern line of the dry region.

It must appear irrational to any one, after a moment's reflection, that the settlement of five or six thousand people in a county usually twenty-four by thirty-six miles in dimensions, and the tillage of a small part of its area, would so materially increase the rainfall in the brief period of ten or twenty years as to make agriculture successful and profitable where before it was not possible. Extending these limits to the wide expanse of States does not make the idea any more tenable. Yet on such conditions as these the theory as applied to our plains is based. The reports of