MECHANICAL PARADOXES. 



Or if it be pressed sideways, it can only trans- 

 mit this pressure sideways to objects beyond 

 it in the direction in which the pressure is 

 exerted upon it. 



Indiarubber, having in an imperfect degree 

 some of the properties of fluids, can transmit 

 some of the pressure put upon it in new direc- 

 tions. Thus, if a round ball of solid indiarubber 

 be placed in a square box whose sides it just 

 touches, and be then forcibly pressed upon, 

 it will swell sideways and transmit sideways 

 to the sides of the box some of the pressure 

 put upon it. 



But a fluid when pressed upon transmits 

 the full pressure equally in all directions. A 

 little consideration will provide familiar illus- 

 tration of this. How is it that water tends 

 so powerfully to force open a dock gate or 

 lock gate, or to burst the dam of a reservoir ? 

 The water at a given distance down the inside 

 of the gate is pressed downwards by its own 

 weight and by the weight of the water above 

 it. This pressure it transmits not only down- 

 wards to the water beneath it, and eventually 

 to the bottom, but also sideways, on three 

 sides to the water adjacent, and on the fourth 

 side to the dock gates, so that the pressure 

 against the gates is greater the deeper we go 

 from the surface. 



How is it that a ship floats in the dock or in 

 the sea ? The weight of the water beside it, 



78 



