OF HYDRGSTA 



113 



B 



LECTURE V 



OP HYDROSTATICS, ANT) HYDRAULIC MACHINES, IN 

 GENERAL. 



THE science of hydrostatics treats of the nature, gravity, 

 pressure, and motion of fluids in general ; and of weigh- 

 ing solids in them. 



A fluid is a body that yields to the least pressure or 

 difference of pressures. Its particles are so small, that 

 they cannot be discerned by the best microscopes ; they 

 are hard, since no fluid except air or steam, can be press- 

 ed into a less space than it naturally possesses ;" and 

 they must be round and smooth, seeing they ^ 

 are so easily moved among one another. 



All bodies, both fluid and solid, press down- 

 wards by the force of gravity : but fluids have ^ 

 this wonderful property, that their pressure up- 

 wards and sidewise is equal to their pressure 

 downwards ; and this is always in proportion 

 to their perpendicular height, without any 

 regard to their quantity ; for, as each par- 

 ticle is quite free to move, it will move towards 

 that part or side on which the pressure is least. 

 And hence no particle or quantity of a fluid can 

 be at rest, till it is every way equally pressed. 



To shew by experiment that fluids press 

 upward as well as downward, let A B be a 

 long upright tube filled with water near to its 

 top ; and C D a small tube open at both ends, 

 and immersed into the water in the large one: 

 if the immersion be quick, you will see the 

 water rise in the small tube to the same height 

 that it stands in the great one, or until the sur- 



Note 44. Subsequent experiments have proved that water is com- 

 pressible, and a variety of interesting facts connected with this sub- 

 ject, will be inserted at the close of the Lecture. 



8 



Definition 

 of a fluid 



Fluids 

 press as 

 much iip- 

 waid as 

 down- 

 ward. 



