HYDROSTATICS. 



creased, although nothing whatever, 

 either solid or fluid, is added to it. 

 The cylindrical vessel A B C D, ( fig. 7.) 



Jiff- 7. 



has a tube H closely fitted into its top, and 

 a rod E K fixed to a plate F G, moving 

 up and down, water-tight, in the vessel. 



The plate being at the bottom C D, 

 water is poured into the vessel, so that 

 it rises nearly to A B, but does not rise 

 in the tube. It is then balanced by a 

 weight in the scale L. If the rod E K 

 is drawn up so as to raise the plate, and 

 force some of the water into the tube, 

 the water will seem to weigh more 

 than it did ; and to restore the balance, 

 more weight must actually be put into 

 the scale L. If the vessel is three inches 

 diameter, every inch that the water 

 rises in the tube will require more 

 than four ounces to be added to the 

 weight, whatever be the bore of the 

 tube ; for the pressure of the water 

 in all directions will be increased by 

 the weight of a body of water, whose 

 height is the height of the water in the 

 tube, and whose base is the extent of 

 the surface of the water pressing on 

 the top A B of the vessel. Now the top 

 being three inches diameter, its surface 

 is about 7 square inches ; and a portion 

 of water one inch high, and 7^ square 

 inches broad, is 7 cubic inches of wa- 

 ter, which weigh about four ounces. 

 Thus, raising the rod a foot will add 

 three pounds to the apparent weight of 

 the water. 



This principle, from its extraordi- 

 nary illustrations, is called the Hy- 

 drostatical paradox; paradox being 

 a word from the Greek, and signifying 

 something, which, though true, ap- 



pears when first considered to be un- 

 true. When we are told that any quan- 

 tity of water, however small, may be so 

 employed as to balance any quantity 

 of water, however great, we are at first 

 star! led by the apparent impossibility of 

 the statement. But when we come to 

 examine it more closely, we find it to be 

 accurately true ; for the small tube in 

 the foregoing figures may be made ever 

 so narrow, and to hold ever so little 

 water, while the wide tube communi- 

 cating with it may be made ever so large, 

 and holding ever so much water ; and 

 the level at which the water stands in 

 both tubes will be the same. So in the 

 scales you may plunge as large a body 

 as you please into the vessel of water, 

 and leave as little water in the vessel as 

 possible ; still, if what you leave stands 

 as high as the whole quantity stood, 

 it will, by weight and pressure together, 

 produce as much effect as the whole 

 quantity of fluid. 



Every thing, under these circum- 

 stances, depending upon the height 

 and the surface, and very little upon 

 the bulk of the fluid, we may easily 

 perceive what mischief may be done 

 by a very small quantity of water, 

 if it happens to be applied or distri- 

 buted, so as to stand high, in however 

 thin a body or column, and to spread over 

 a wide but confined and shallow space. 

 Suppose that, in any building, a very 



