134 



WAVE IMPACT ON 



Actually the maximum pressure attained will be less than this, 

 because energy is lost by eddy formation at the entrance to 

 such a passage ('5v 2 -r 2g if the edges are sharp and normal to 

 the face) and by friction during motion up the passage, while it 

 is probable that except in a joint of very small cross-sectional 

 area the motion of the water will be rather of the type indicated 

 in Fig. 1, 6, than in Fig. 1, a. Such a type of motion, leading to 

 backward displacement of the air over the top of the advancing 

 column would produce further loss of energy in eddy forma- 

 tion. It appears probable that hi no case could the loss of 

 energy, due to these various causes, amount to less than 

 25 per cent, of the initial energy of impact, and that it would 

 normally amount to 50 per cent, or even more. The effect of 

 such losses on the maximum pressure obtainable in this way 

 is shown in the following table : 



In any case, however, should the face pressure be maintained 

 for a sufficient length of time, water will be forced along 

 the crevice until the internal pressure is equal to the face 

 pressure. 



Experiments by the authors, the results of which are given 

 at a later stage, showed that using a light piston to simulate 

 the state of affairs, shown in Fig. 1, a, the maximum pressure 

 attained by air compression was 2 '48 times the face pressure, 

 while without this piston it was 2 '05 times the latter pressure. 

 As the state of affairs in these experiments was particularly 



