74 THE POPULAR SCIENCE MONTHLY. 



est land on the earth, and then whence comes the flow to supply that ? 

 The mere statement of the case proves the existence of some force in 

 nature other than hydrostatic pressure by which these vast bodies of 

 water are driven to the surface. This hydrostatic pressure Pro- 

 fessor Buckland thus illustrates and explains : " The portions of a 

 water-logged, porous bed between two beds of clay may be illustrated 

 by a tea-saucer placed within another tea-saucer, and having the nar- 

 row space between filled with sand and water. If a hole were drilled 

 through the bottom of the upper saucer and a quill or small pipe fixed 

 vertically in the hole, water would rise in the pipe to the level at 

 which it stands within the margin of the lower saucer, its rise being 

 caused by the same hydrostatic pressure that raised the water in the 

 well at Southampton, coming from subterranean sheets of the fluid 

 which exists in the fissured chalk-beds of the Hampshire basin, as 

 they do also in the chalk under the basin of London." 



Should these exceptional and assumed conditions occur in nature, 

 the result would be substantially as indicated ; but, as will be seen at 

 a glance, the flow from a well sunk under such circumstances would be 

 limited to the amount of water between the two saucers, and this will 

 be limited to the quantity of rainfall. Since flowing wells and springs 

 are seldom if ever thus limited, we infer that the case supposed does 

 not occur. But whether it does or not is of no importance, since it in 

 no sense satisfies the conditions of the "majestic column" at Grenelle, 

 and other cases where the flow is perpetual. We must, therefore, look 

 for some other force to explain this class of phenomena. Professor 

 Faraday followed Professor Buckland's lead six years later. M. Gar- 

 nier, the celebrated French engineer, whose essay in 1822 upon this 

 subject took the governmental prize, also takes this position ; as does 

 Dr. Halley. This theory we combat not merely from speculative mo- 

 tives, but in the interest of public health. 



Various other theories have been advanced besides hydrostatic 

 pressure. Aristotle and Seneca suggested the central heat of the 

 earth. This theory has been more fully and scientifically stated by 

 E. S. Chapin, in his work on gravity. But this is not the force that 

 we seek. It is inadequate, as the following simple experiment shows : 

 If a moderately flowing spring is surrounded by an air-tight iuclosure 

 which shall contract, and terminate in a tube, and this tube be allowed 

 to have a discharge some distance beloAv the surface of the water in 

 the spring before its inclosure, it will be found that the water-flow 

 from the spring has been greatly increased, though no change of tem- 

 perature has occurred. Again, it has been suggested that the over- 

 flow of springs was due to capillary action ; but this 'can hardly need a 

 serious consideration in view of the amount and character of those 

 overflows. 



There are three classes of water to be taken into account in this 

 discussion : 1. The surface waters mainly influenced by rainfalls ; 2. 



