war BO sPIiI^^GS and wells overflow? 79 



countries through which they pass." This has been more than con- 

 firmed 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 con- 

 nection 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 l»ss by 

 absorption and evaporation — great and navigable rivers, throughout 

 the longest dry season ; and the Nile has no tributaries for five hun- 

 dred miles of its course. 



And, lastly, from the highest mountains in the world — the Hima- 

 layas — out of their highest points, great cataracts and streams have 

 poured and still do pour, with an abundance that not only is astonish- 

 ing, but that wovdd exhaust any possible reservoirs at their extreme tops. 

 Since this is the highest land of the Avorld, 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 sur- 

 face whence we intend to bore, we can not hope to obtain an over- 

 flowing fountain." And, as if conscious that there might be some mis- 

 take 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 I, h, 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 ques- 

 tion 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 represent- 

 ing 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 tlie point A. 



