HYDROSTATIC PRESSURE EXEMPLIFIED IN SPRINGS, &C. 439 



the fluid, whose height is the elevation of the fluid between the bodies, 

 measured to the extreme points of contact of the interior fluid, and 

 minus the elevation of the fluid on the exterior sides. The elevation, 

 however, must be reckoned negative when it changes into a depression, 

 as is the case with mercury and other metals in a state of fusion, as 

 has been observed elsewhere. 



HYDROSTATIC PRESSURE EXEMPLIFIED IN SPRINGS AND 

 ARTESIAN WELLS. 



560. The atmosphere is the uninterrupted source of communication 

 between the sea and the earth ; it is the capillary conductor of water 

 from the ocean to the land. Water ascends in the form of vapour, 

 and descends as dew or rain upon the earth, which however it pene- 

 trates but a small depth, except by fissures and permeable strata, which 

 conduct it to subterranean reservoirs, whence it again issues as in the 

 discharge of springs; or when the earth is bored through, it rises as 

 in wells. Some wells are fed by land springs springs of shallow 

 depth ; others are fed from the percolation of water through strata 

 that act as conduits, conveying a current of the fluid through their 

 permeable texture from one high land to another. Hence it is, that 

 in valleys and champaign districts, very deep wells are dug, in order 

 to arrive at those great feeders, where the hydrostatic pressure sends 

 the water up with amazing force. In some cases we can trace the 

 source of springs ; and with the help of FATHER KIRCHER'S Mundus 

 Subterraneus, a man of a fanciful wit might present the public with a 

 very learned treatise on Natural Hydraulics and Artesian Wells.* 



561. As regards rock springs, we know of none that surpass the 

 sources of the Scamander, in Asia Minor, an account of which will be 

 found in some notes accompanying Poems of the Rev. Mr. Carlyle, who 

 saw the stream of the Menderi issuing from a cave surrounded with 

 trees, and tumbling down the crags in a foaming cascade ; for there 

 the cavern that " broods the flood divine," discharges its sacred stores 

 by two large openings in the rock, which leads into the cavern. Upon 

 entering the recess, two other openings, nearly answering to the out- 

 ward ones, like arches in a cloister, present themselves to the sight; 

 and through one of them, in a basin below, the traveller perceives the 



* From Artois (the ancient Artesium of Gaul), where perpetually flowing artifi- 

 cial fountains are obtained, by boring a small hole through strata destitute of water, 

 into lower strata loaded with subterraneous sheets of this important fluid, which 

 ascends by pipes let down to conduct it to the surface. 



