164 PRESSURE OF LIQUIDS BY THEIR WEIGHT. 



the smaller cylinder is however obviously impracticable 

 and the smaller cylinder is therefore constructed like ; 

 pump, so that the required quantity of water can b< 

 pressed into the larger cylinder by a number of sue 

 cessive comparatively short strokes of the plunger 

 The essential parts of this contrivance are indicated ii 

 fig. 113, but cannot be explained until a subsequent par 

 of this work ; nor is it possible to enter here more full 1 

 upon the various details which must be attended to ii 

 the construction of a hydraulic press. 



The pressure which we have hitherto considered ha 

 been applied externally, and has been equally trans 

 mitted through the mass of the liquid. But liquid 

 have weight, that is, they are acted on by gravity lik 

 other bodies, and hence it is evident not only that th 

 upper portions of a liquid mass press upon those belo^ 

 but also that the pressure at any point is greater th 

 deeper it is below the surface of the liquid. 



The pressure is the same at all points which have eqm 

 depths below the surface, that is, at all points of the san 

 horizontal layer, and at different depths the pressure 

 proportional to the depth. 



This pressure is also transmitted equally in all dire< 

 tions, although caused by a force which acts vertical!; 

 Each particle which is pressed is from the nature < 

 a liquid capable of moving in any direction, hence 

 In order that a liquid may remain at rest, each molecul 

 of the mass must be subject in every direction to equal <m\ 

 contrary pressures. Whenever the pressure upon 

 molecule in one direction is greater than that i 

 another, the molecule will move. 



In order to investigate the pressure which liquic 

 exert by their weight upon the horizontal bottom, of 



