^3 y (<d- (cos a- sin a) = K2 K4 A 



Consequently 



/fj Ccos & ~ s//?3.) (of- O 



The weight of the stone in air, P, is 



P.H.y^c/^Hs'^^ 



^S (cos <a~s//7^)3(c/-/)3 



or setting _ - 



we obtain the soiight-for formula 



which gives us the necessary weight for the stones in terms of the 

 elements of the problemo 



If we assume a case such that the wave does not break in the form 

 considered, viz, a very steep slope, or from some other cause whatso- 

 ever, and as a consequence the damage to the stones is occasioned by 

 the descent of the water along the slope, then the force P' of the 

 current flowing parallel to the slope over the stone or stones affected 

 would approximate; 



/=:- H;sg^ = K'^As 



The coefficient K' will be much less than unity, since the roughness 

 and permeability of the rock-fill causes a reduction in current 

 velocity. 



The resistance of the stone or stones to downward displacement 

 is: 



R=N-F = Pg cos A 



The component D will continue to bes 

 D= Ps sinSL 



and the equation of strict equilibrium will be 



D + P'=R 

 or 



P^ sin a. + KpAS = Pg cos a. 



10 



