HYDROSTATICS. 



in a box, so as to touch its sides and 

 bottom ; then a brass plate is laid loosely 

 upon the bladder, and a hundred pounds 

 weight or more is laid upon the plate ; 

 the wax and the egg though pressed by 

 the water with this weight, yet being 

 pressed equally in all directions, are 

 not in the least either crushed, or al- 

 tered in shape. 



CHAPTER III. 



Consequences of the Principle Hy- 

 drostatic Paradox Levelling. 



IT is a consequence, or rather another 

 example of the same principle, that if 

 you poise in a balance a pitcher full 

 of water, by loading the opposite scale, 

 and then hold in the pitcher a block of 

 wood, or any other substance nearly 



the size of the pitcher, but so that it 

 shall not touch its sides or bottom, 

 although almost all the water will thus 

 have been made to run over the sides, 

 and only a spoonful may remain, yet the 

 scales will continue balanced ; and this 

 without any regard to the weight of the 

 body plunged into the water, and though 

 you hold it entirely clear of the pitcher, 

 so that it touches it in no place ; for 

 the effect will be the same if what you 

 plunge in be scooped hollow, and made 

 water-tight, so as to displace the greater 

 pail of the water. A bladder blown 

 up, and tied fast, for example, and held 

 down in the water, so as to leave only a 

 spoonful suiTOunding it, will keep the 

 scales balanced just as well as a block of 

 lead the same size. Thus if E F (fig. 6 .) 

 be a balance with two scales E and F, 

 you may put a jar of water A in one^ of 

 the scales F, and " 



in the other scale E. Then pour out 

 all the water but an inch or two at the 

 bottom, so that it stands at B instead 

 of A, as in the jar B ; the weights in 

 E will be much too heavy for it : now 

 take a crooked piece of wood GHI, 

 and place it so that the thick part I is 

 plunged to near the bottom of the jar, 

 and make the water rise from b to a, 

 as high as it stood before in the full 

 jar A ; the scale F will again balance 

 the weights in the scale E, although 

 there is only the small quantity of water 

 in it that surrounds the block. And this 

 does not depend on the weight of the 

 block I, which is entirely supported by 

 the stand G K ; for whether it be made 

 of wood or lead or card, the water, if it 

 stands as high round it, balances the 

 same weight as before. An easy way 

 of trying this is, by putting a tumbler 

 full of water in one scale, and balancing 

 it with weights in the other, then pour- 

 ing out all but two or three table- 

 spoonsfull ; the scale with the weights 

 will of course sink ; but if you now 



put a smaller empty tumbler in the 

 other, so as to make the water rise 

 round it to the brim, still holding it 

 when immersed, the balance will be 

 restored ; and the small tumbler will 

 not make the scale weigh heavier if it 

 be filled with lead-shot; nor will it 

 make the scale lighter, if, instead of 

 glass, the smaller tumbler is made of 

 thin wood or card. 



There is yet another way of illustrating: 

 the effects of this property of fluids. 

 "\W have seen how the displacing any 

 portion of a fluid by a fixed solid, what- 

 ever be the weight of the solid, produces 

 no difference in the weight of the fluid, 

 provided it stands at the same height as 

 before , and how, raising the height of 

 the fluid by plunging a solid into it, in- 

 creases its pressure, or apparent weight. 

 If the fluid is raised by pressing or 

 forcing it upwards, in however thin a 

 column, provided the vessel be kept 

 full, and closed in all directions, the 

 pressure of the fluid will be increased, 

 and the weight of the vessel will be in.* 



