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HYDROSTATICS, 



By hydrostatics, in general, is meant the science 

 which treats of the mechanical properties of fluids. 

 Strictly speaking, however, hydrostatics treats of 

 the weight and equilibrium of fluids at rest. When 

 that equilibrium is destroyed, motion ensues ; and 

 the science which considers the laws of fluids in 

 motion, is called hydraulics. 



A fluid is defined to be, a body whose parts yield 

 to any impression, and, in yielding, are easily moved 

 amongst each other. 



Fluids are of two kinds : non-elastic and incom- 

 pressible fluids, such as water, oil, mercury, &c. ; 

 and elastic and compressible fluids, as air of dif- 

 ferent sorts. 



Here it must be observed that the class of fluids 

 denominated incompressible, are not absolutely 

 so; but they are compressible in so slight degree, 

 that it may be disregarded in practical cases, so 

 that this division is still retained. 



From the expansion and contraction of water 

 by heat and cold, it might have been inferred that 

 it was compressible by some means : but from 

 some experiments formerly made by the Academy 



