Page:Popular Science Monthly Volume 16.djvu/89

 countries through which they pass." This has been more than confirmed by the discoveries of Dr. Livingstone and Mr. Stanley in the heart of Africa, where some of the greatest rivers of the world flow out of the highest part of the African Continent. And in this connection the important element of the rainfall is not ignored. These countries are subject to long and weary droughts. But, while the volume of these great rivers is sensibly affected by the rain and the want of it, they continue to flow within their banks, subject to loss by absorption and evaporation—great and navigable rivers, throughout the longest dry season; and the Nile has no tributaries for five hundred miles of its course.

And, lastly, from the highest mountains in the world—the Himalayas—out of their highest points, great cataracts and streams have poured and still do pour, with an abundance that not only is astonishing, but that would exhaust any possible reservoirs at their extreme tops. Since this is the highest land of the world, no such higher source is possible. Hence the conclusion is inevitable that some force not yet identified exists to which these great overflows are due. It should be remembered that up to this time it is generally held, to use the words of M. Garnier, that "unless there be a reservoir higher than the surface whence we intend to bore, we can not hope to obtain an overflowing fountain." And, as if conscious that there might be some mistake about this theory, he says further that gases may force water up, by which he means to suggest a cause other than hydrostatic pressure. But the experiment which may be seen any day at the gas-works will show that gases do force water down when both are inclosed by a common receiver. There is no conceivable situation in which gases could be expected to force subterranean water in a direction opposed to gravity in such quantities as to satisfy the conditions.

Is it possible, then, to point out any other force in nature which not only may, but which positively must, force waters out of springs at high elevations?

Let a, a, a, be a great circle of the earth attained by passing a plane through the earth's center C, perpendicular to its axis, and b, b, b, the circle cut by the same plane through the inner surface of the earth's supposed crust. In order to obtain room in the figure for illustration, this section is exaggerated. Let the line A B represent the force of gravity, and A E the centrifugal force, at the point A, which will operate in the direction of the tangent A G. These two forces, for the purposes of this discussion, may be assumed to be equal, as the question of their relative intensities does not enter into the problem. Erect upon the line A B the square A B D E, and draw the diagonal A D produced to F. By a well-known law we shall have A D representing the resultant of the forces A B and A E—that is, the line A D will represent the direction A F, and the intensity of the resultant of the force of gravity and the centrifugal force, acting at the point A.