ct g - 1 = 1.95 ^15 x 2.7" = 0.248 

 Vl + ct 2 a 1.7 V 4000 



whence the batter should be ctoc * 1.4-3 



For that situated below Hj, = - 14 ms 



ct a - 1 = 1.40 3 /l5 x ?.7~ - 0.282 



VTT 



ct'oc 1.7 v iooo 



whence the batter should be eta ■ 1.51« 



For the deep zone H r < - 18 m, one obtains a weight: 



P = 15 x 1.00 3 x 2.7 - 94 kilograms 



^) x 1.7 3 



likewise quite acceptable, and the weight corresponding to the 

 toe of the dike will bej 



P = 15 x 0.33 3 x 2.7 -3.4 kilograms, 

 x 1.7 3 



In this way we obtain a theoretical profile, shown in Figure 3' 

 similar to 3, even more closely approximating the real profile; but 

 the really interesting fact is that both figures, whose calculated 

 wave heights differ by less than 8 per cent, a degree of approxima- 

 tion that we consider difficult for anything practical to really ex- 

 xeed, are now authentically confirmed by the very important direct 

 observation from this interesting compilation. It is also now con- 

 firmed undoubtedly, through authentic direct observation and despite 

 the simplifications one is forced to introduce into the complex 

 subjects of maritime engineering, that the degree of approximation 

 really obtained is superior to that of many calculations of 

 engineering on terrestrial subjects, in which, even legally there 

 are imposed large safety factors, generally greater than two and 

 frequently approximating three. 



In the rock fill dikes the proportional increase of cost 

 occasioned by these always convenient safety factors would not be 

 greater than that for terrestrial works, and moreover, their cost 

 would be recovered in no long time, on the basis that, by placing 

 somewhat heavier stones or blocks the movements and consequent 

 expenditures diminish and thus very costly outlays for maintenance 

 are saved. 



For these reasons it seems advisable, despite the very 

 satisfactory confirmation just made arid which one must remember 

 refers to the strict equilibrium limit, to adopt at least a re- 

 duced factor of safety of 1.5 on the coefficients N, so that they 



19 



