HYDROSTATICS. 



129 



What is the 

 principle and 

 action of the 

 Hydrostatic 

 Bellows ? 



The principle that the pressure exerted by a column of 

 water is as its height, and not as its quantity, may be also 

 illustrated by the Hydrostatic Bellows, Fig. 109. This con- 

 sists of two boards, B C and D E, united together by means 

 of cloth, or leather, A, as in a common bellows. A small ver- 



FlG. 109. 





tical pipe, T, attached to the side communicates 

 with the interior of the bellows. Heavy weights, 

 "W W, are placed upon the top of the bellows 

 when empty. If water be poured into the verti- 

 cal pipe, the top of the beUows, with the weights 

 upon it, will be hfted up by the pressure of the 

 water beneath ; and as the height of the column 

 of water increases, so in like proportion may tho 

 weights upon the top of the bellows be increased. 

 It is a matter of no consequence what may be the 

 diameter of the vertical tube, since the power of 

 the apparatus depends upon the height of the col- 

 umn of water in the small tube, and the area of 

 the board, B C ; that is, the weight of a small col- 

 umn of water in the vertical pipe, T, will be cajiable 

 of supporting a weight upon the board, B C, greater 

 than the weight of the water in the pipe, in the same 

 D proportion as the area of hoard B C is greater than 

 the sectional area of the bore of the pipe. Thus, if 

 the area of the bore of the pipe be a quarter of an inch, and the area of the 

 board forming the top of the bellows a square foot, then the proportion of the 

 pipe to the board will be that of 576 to 1 ; and, consequently, the weigni 

 capable of being supported by the board will be 576 times -piG. 110. 

 the weight of the water contained in the pipe. 



In this manner a strong cask, a, Fig. 110, 

 filled with liquid, may be burst by a few 

 ounces of water poured into a long tube, b c, 

 communicating with the interior of the cask. 

 This law of pressure is sometimes exhibited 

 on a great scale in nature, in the bursting of rocks, or mount- 

 ains. Suppose a long vertical fissure, as in Fig. Ill, to com- 

 municate with an internal cavity formed in a mountain, with- 

 out any outlet. Now, when the fi.'sure and cavity become 

 filled, an enormous pressu'-e is exerted, sufficient, it may be, 

 to crack, or disrupture, the whole mass of the mountain. 



The most striking effects of the pressure of the water at 

 great depths are exhibited in the ocean. If a strong, square 

 glass bottle, empty and firmly corked, be sunk in water, its 

 sides are generally crushed in by the pressure, before it has 

 reached a depth of CO feet. Divers plunge with impunity to 

 certain depths, but there is a Umit beyond which they can not sustain tho 



6* 



V7 



What are Il- 

 lustrative ex- 

 amples of the 

 pressure of 

 liquids? 



