EQUAL TRANSMISSION OF PRESSURE. 7 



the motion of the liquid along it. Then it may be assumed 

 as self-evident, that if any force be applied to the piston A, 

 perpendicular to its surface, and directed inwards, it will 

 push the liquid forward, and thus produce a pressure on the 

 piston B, which will drive it out of the tube, unless there 

 be an equal force at B, pushing in the opposite direction, to 

 counteract the force at A and keep the liquid at rest. This 

 property of liquids is a direct result of experiment. 



(2) Let ABCD represent a closed vessel of any shape, 

 filled with a liquid ; let A and B be any two points in the 

 surface of the vessel, and let two circular holes be made at 

 these points, having the same area; 

 into these let two short tubes be in- 

 serted, each tube entering a little way 

 into the liquid, and provided with a 

 piston that fits it accurately, and 

 which may move within it with the 

 utmost freedom. Now suppose that 

 the two orifices, A and B, are connect- F ' 9 ' 3 



ed by a tube of liquid AEB, in the interior of the vessel, of 

 uniform bore, and of any form, and imagine all the liquid 

 in the vessel, except that contained in the tube, to be solidi- 

 fied. This will not affect the equilibrium (Art. 5). But, 

 under these circumstances, if a pressure be applied to the 

 piston A, and directed inwards, it will, as shown in (1) 

 above, be transmitted to B, and will require an equal force 

 at B to counteract it and keep the fluid at rest. 



If we suppose the piston B, to be taken anywhere on the 

 surface, it is evident from what has been said that any press- 

 ure applied to the 'piston A will be transmitted to B, and 

 will require an equal pressure at B to counteract it. It is 

 also evident that if we -have several openings, each equal to. 

 B, closed by pistons, any pressure applied to one piston will 

 be transmitted undivided to every other piston, and will 

 require an equal pressure at each of those pistons to coun- 

 teract it, The above reasoning remains true, no matter 



