202 



MACHINERY IX CONNECTION WITH WATER. 



artificially, througli which the water is driven up to the 

 surface, as at a, forming what are termed Artesian Wells. 

 The head of water which supplies them may be many 

 miles distant, the plac of discharge being on a lower 

 level. It has sometimes been found necessary to bore 

 more than a thousand feet downward before obtaining 

 water which will flow out freely at the surface of the earth. 



DETERMINING THE PRESSURE ON GIVEN SURFACES. 



The pressure of liquids upon any given surface is ahvays 

 exactly in proportion to the height, no matter what the 

 shape of the vessel may be. If, 

 for instance, the vessel a (fig, 

 228), be one inch in diameter, 

 and the vessel b be three inches 

 in diameter, the water being 

 equally high in both, the press- 

 ure on the whole bottom of b 

 will be nine times as great as on 

 the bottom of a ; or any one inch of the bottom of b will 

 receive as great a pressure as the bottom of a. Again, if 

 the vessel c, broad at the top, be narrowed to only an 

 inch in diameter at bottom, the press- Fig. 229. 



ure upon that inch will still be the 

 same, most of the weight of its con- 

 tents resting "Against the sides, d d. 

 If the vessel, A (fig. 229), be filled 

 with water to a height of fourteen 

 inches, the pressure will be half a 

 pound on every square inch of the 

 bottom, or upon every square inch 

 of the sides fourteen inches below the surface. If the 

 tube, C, be an inch square, the water will be driven into 

 it with a force of half a pound, and will press with that 

 force iigainst the one-inch surface of the stop-cock, C. If 



