HYDROSTATICS. 



fig. 10. 



than the cylinder L, having at the part 

 I a valve opening towards the cylinder; 

 and D is the handle of a forcing pump, 

 C H, by means of whose piston water 

 can be forced under the piston A. K 

 represents another valve which, re- 

 lieved from the pressure of the adja- 

 cent screw, allows the water to flow 

 back again through the pipe M into 

 the reservoir G, when the solid A is 

 required to descend. The pressure 

 upon the bottom of the piston at L, 

 will be* to the pressure upon the water 

 in H, by means of the piston rod 

 C, as the size of the under surface 

 of A, to the size of the surface H, or 

 as the section of that part of the cylin- 

 der occupied by the respective pistons. 

 It is therefore as if we had to compare 

 he pressure of water of the same depth, 

 but on different surfaces ; and this is in 

 proportion to the surfaces. If the pis- 

 ton H is half an inch diameter, and the 

 cylinder A one foot, the pressure of the 

 water on the bottom of the cylinder 

 will be to the pressure of the smaller 

 piston on the water at H, as a square 

 foot to a quarter of a square inch (the 

 areas of circles being as the squares of 

 their diameters), that is, as 144 square 

 inches to a quarter of a square inch, 

 or as 576 to 1; and therefore if the 



pressure of a ton weight be given by 

 means of the lever D, the cylinder A 

 will be moved upwards, and be forced 

 or pressed against whatever is placed 

 in the space above it, with the weight of 

 576 tons. It is evident that this pow-er 

 may be increased without any other 

 bounds than the strength of the ma- 

 terials, either by machinery, which 

 will increase the force upon the water 

 in the pump C H ; or by increasing the 

 disproportion between the diameters of 

 the two pistons, or by both. Thus, if 

 a pressure of two tons be given by a 

 pump of only a quarter of 'an inch, 

 and the cylinder be a yard in diameter, 

 the pressure upwards will be equal to 

 the weight of 41,472 tons; and this 

 prodigious effect will be produced by 

 the agency of less than a pound of 

 water. Such a force is much too great 

 for the strength of any materials which 

 we can employ. Bat within the space 

 of nine or ten inches square and a foot 

 high, a force of 5 or 600 tons may easily 

 be brought to bear upon any substance 

 which it is wished to press, to tear up, 

 to cut in pieces, or to pull asunder. 



Upon the tendency of all the parts of 

 fluids to dispose themselves in a plain 

 or level surface, depends the making of 

 levelling instruments, or instruments for 



