INTRODUCTION TO HYDROSTATICS. 



SECTION I. On the Mechanical Properties of Fluids. 



THE science of the mechanical properties of fluids is called Hydrostatics. 

 A fluid is a substance which yields to the slightest pressure. If you dip 

 your hand into a basin of water, you are scarcely sensible of meeting 

 with any resistance. Fluids, generally speaking, are bodies of less density 

 than solids. From the slight cohesion of their particles, and the facility 

 with which these slide over each other, it is conjectured, that they must be 

 small, smooth, and globular ; smooth, because there appears to be little 

 or no friction among them ; and globular, because touching each other 

 but by a point would account for the slightness of their cohesion. 



Fluids are divided into two classes, distinguished by the names of 

 liquids and elastic fluids, or gases, which latter comprehends the air 

 of the atmosphere, and all the various kinds of air with which 

 chemistry makes us acquainted. We shall confine our attention at 

 present to the mechanical properties of liquids or non-elastic fluids. 



Water, and liquids in general, are little susceptible of being compressed, 

 or squeezed into a smaller space than that which they naturally occupy. 

 This is supposed to be owing to the extreme minuteness of their particles, 

 which, rather than submit to compression, force their way through the 

 pores of the substance which confines them, as was shown by a cele- 

 brated experiment, made at Florence many years ago. A hollow globe 

 of grold was filled with water, and on its being submitted to great pressure, 

 the water was seen to exude through the pores of the gold, which it 

 covered with a fine dew. But more recent experiments, in which water 

 has been confined in strong iron tubes, prove that it is susceptible of 

 compression. 



Liquids are porous, like solid bodies, but the pores are too minute to be 

 discovered by the most powerful microscope. The existence of pores in 

 liquids can be ascertained by dissolving solid bodies in them. If you 

 melt some salt in a glass full of water, the water will not overflow, 

 because the particles of salt will lodge themselves in the pores of the 

 liquid, so that the salt and water together will not occupy more space than 

 the water did alone. If you attempt to melt more salt than can find room 

 within these pores, the remainder will subside at the bottom, and occu- 

 pying a space which the water filled before, oblige the latter to overflow. 

 Spirit of wine may also be poured into water without adding to the bulk, 

 as the spirit will introduce itself into the pores of the water. 



Fluids show the effects of gravitation in a more perfect manner than 

 solid bodies ; the strong cohesive attraction of the particles of the latter 

 in some measure counteracting the effect of gravity. In a table, for 

 instance, the strong cohesion of the particles of wood enables four slender 

 legs to support a considerable weight. Were the cohesion so far destroyed 

 as to convert the wood into a fluid, no support could be afforded by the 

 legs ; for the particles no longer cohering together, each would press 

 separately and independently, and would be brought to a level with the 

 surface of the earth, 



