UTILITY OF HYDROSTATICS. 



A few years ago, a friend of mine, when in Ire- 

 ,arid, performed this experiment to convince an 

 English gentleman, who called in question the 

 principle, and who laid a bet of fifty pounds that 

 it would not succeed. A hogshead, above 3 feet 

 high, and above 2 feet wide, was filled with 

 water ; a leaden tube, with a narrow bore, be 

 tween 20 and 30 feet long, was firmly inserted 

 into the top of the hogshead ; a person, from the 

 upper window of a house, poured in a decanter 

 of water into the tube, and, before the decanter 

 was quite emptied, the hogshead began to swell, 

 and, in two or three seconds, burst into pieces, 

 while the water was scattered about with im 

 mense force. 



Hence, we may easily perceive what mischief 

 may sometimes be done by a very small quantity 

 of water, when it happens to act according to its 

 perpendicular height. Suppose, that in any 

 building, near the foundation, a small quantity 

 of water, only of the extent of a square yard, has 

 settled, and suppose it to have completely filled 

 up the whole vacant space, if a tube of 20 feet 

 fong were thrust down into the water, and filled 

 with water from above, a force of more than 5 

 tons would be applied to that part of the building, 

 which would blow it up with the same force as 

 gunpowder.* The same effect may sometimes 

 be produced by rain falling into long narrow 

 chinks, that may have inadvertently been left in 

 building the walls of a house ; which shows the 

 importance of filling up every crevice and open 

 ing of a building, and rendering the walls as 

 close and compact as possible. Hence, like 

 wise, similar processes in nature, connected 

 with pools of water in the bowels of the earth, 

 may occasionally produce the most dreadful 

 devastations. For, should it happen, that, in 

 the interior of a mountain, two or three hundred 

 feet below the surface, a pool of water thirty or 

 forty square feet in extent, and only an inch or 

 two in depth, was collected, and a small crevice 

 or opening of half an inch in breadth were con 

 tinued from the surface to the water in the 

 pool ; and were this crevice to be filled with 

 rain or melted snow, the parts around the layer 

 of water would sustain a pressure of more than 

 fix hundred tons, which might shake the moun 

 tain to its centre, and even rend it with the 

 greatest violence. In this way, there is every 

 reason to believe, partial earthquakes have been 

 produced, and large fragments of mountains 

 detached from their bases. 



The principles now illustrated are capable of 

 the most extensive application, particularly in all 

 engineering and hydraulic operations. It is on 

 the principle of the lateral and upward pressure 

 of fluids that the water, elevated by the New 

 River water-works, in the vicinity of London, 

 *fter having descended from a bason in a vertical 



Seeflg. 8- p. 68. 



pipe, and then, after having flowed 1 

 in a succession of pipes under the pavement, is 

 raised up again through another pipe, as high as 

 the fountain in the Temple Garden. It is upon 

 the same principle that a vessel may be filled 

 either at the mouth or at the bottom indifferently, 

 provided that it is done through a pipe, the top 

 of which is as high as the top of the vessel to be 

 filled. Hence, likewise, it follows, that when 

 piers, aqueducts, or other hydraulic works for 

 the retention of water, are to be constructed, it 

 becomes necessary to proportion their strength 

 to the lateral pressure which they are likely to 

 sustain, which becomes greater in proportion to 

 the height of the water to be sustained. Walls, 

 likewise, designed to support terraces, ought tf 

 be sufficiently strong to resist the lateral pressure 

 of the earth and rubbish which (hey are to sus 

 tain, since this pressure will be greater as the 

 particles of earth, of which the terraces are 

 composed, are less bound together, and in pro 

 portion as the terraces are more elevated. The 

 increase of pressure in proportion to the depth 

 of any fluid likewise shows the necessity of form 

 ing the sides of pipes or masonry in which fluids 

 are to be retained, stronger towards the bottom, 

 where the pressure is greatest. If they are no 

 thicker than what is sufficient for resisting the 

 pressure near the top, they will soon give way by 

 the superior pressure near the bottom; and if 

 they are thick enough in every part to resist the 

 great pressure below, they will be stronger than 

 necessary in the parts above, and, consequently, 

 a superfluous expense, that might have been 

 saved, will be incurred in the additional materials 

 and labour employed in their construction. The 

 same principle is applicable to the construction 

 of flood-gates, dams, and banks of every de 

 scription, for resisting the force of water. When 

 the strength and thickness requisite for resisting 

 the pressure at the greatest depth is once ascer 

 tained, the walls or banks may be made to taper 

 upwards, according to a certain ratio founded on 

 the strength of the materials, and the gradual 

 decrease of pressure from the bottom upwards ; 

 or, if one side be made perpendicular, the other 

 may proceed in a slanting direction towards the 

 top. 



From the principles and experiments now 

 stated, we may also learn the reason why the 

 banks of ponds, rivers, and canals blow up, as it 

 is termed. If water can insinuate itself under 

 a bank or dam, even although the layer of water 

 were no thicker than a half-crown piece, the 

 pressure of the water in me canal or pond will 

 force it up. In fig. 8, let A represent the section 

 of a river or canal, and BB a drain running under 

 one of its banks ; it L evident, that, if the bank 

 C is not heavier than the column of water BB,, 

 that part of the bank must inevitably give way. 

 This effect may be prevented in artificial canal? 

 by making the sides very tight with clay heavily 



