HYDROSTATICS AND HYDRAULICS. 45 



HYDROSTATICS AND HYDRAULICS. 



Hydrostatics and Hydraulics defined Pressure of Fluids, and peculiar properties 

 Specific gravity of Bodies Motion of water in pipes Sucking Pump 

 Forcing Pump Siphon Jets, 4cc. 



HYDROSTATICS is that science which treats of the na- 

 ture, gravity, and equilibrium of fluids, and of the 

 weighing of bodies therein. Hydraulics treats of the 

 force and velocity of fluids in motion. 



Fluids are those bodies which possess a perfect free- 

 dom of motion, and whose parts yield to any impression. 

 They are divided into elastic and non-elastic. Air, vapour, 

 and gases, are elastic, as their volume may be diminished 

 by pressure. Mercury, water, &c. are non-elastic or 

 incompressible, except to an inconsiderable amount.* 



It is peculiar to fluids, that they do not press only in 

 a perpendicular direction, like solids, but upwards, 

 laterally, and in every direction. The sides of canals 

 are on this account sometimes blown up, as it is termed ; 

 the water, by gradually washing away the earth, in time 

 forms a kind of hollow, the pressure becomes too great 

 for the bank to withstand, and it is forced up and falls 

 into the canal. 



The pressure of fluids is not according to their bulk, 

 but according to their perpendicular height, combined 

 with the area of the base. If two vessels be filled with 

 water or any other fluid, the one of a cylindrical and 

 the other of a conical shape, provided the bases and 

 perpendicular heights are equal, the perpendicular pres- 

 sure of the liquid will be equal : should it happen that 

 their contents become frozen, then the pressure on the 

 bottom of the cylindrical vessel will be three times as 

 great as that on the bottom of the conical vessel, the 

 volume of a cylinder being equal to three times that of 

 a cone of the same base and height. If a long tube of 

 only half an inch in diameter be inserted into a large 

 cask of water and made air-tight, by pouring water into 



* Perkins is said to have compressed water one-twelfth with 2000 

 atmospheres. 



