taken away from the wave on the part of the coast whsre the wave- 

 movement reaches the bottom, it is obvious that the energy in the 

 original unbroken waves can be used as a measure of the wave attack 

 on the ocean bottom and the coast. In other words, there must be a 

 relation between the energy contained in the original deep-water wave 

 and the transport of the material on the bottom of the sea| in brief 5 

 between wave energy and material movenent along the coast. However ^ 

 not all the wave energy is used for the material moveirsntj much energy 

 is lost in the generation of foam, heat, electricity j, etc. 



Similarly to the conditions in a ri^'er, the bottom material in 

 the ocean can be moved either suspended in water, or rolling and 

 sliding along the bottom of the ocean. The more violent the sefl , the 

 greater amount of energy in the wave, and the heavier the material it 

 can move. The energy which the wave looses when it first breaks is 

 used partly for disturbing the bottom ^x the ocean and partly to start 

 another direction depending upon the wind„ These coast currents are 

 transferred wave energy, and consequently the effect of the currents 

 is a function of the wave. 



It is not only at the place where the wave breaks that the move- 

 ment of material occurs. Before the ground-water wave breaks, it can 

 move materials not only forwards and back again ^ but also in a certain 

 direction. The reason for this is something which is characteristic 

 of tte ground-water wavej namely, the forward speed of the wave crest 

 is greater than the backward speed of the wave trough - This can be 

 noticed easily by direct observation . When the water is clear, it can 

 be seen from ships that seaweed, etc. suddenly moves rapidly when the 

 wave crest passes, while the return movenent when the wave trough passes 

 is slower and longer lasting. Also, divers can notice siidden strong 

 pressure inwards when the wave passes. This has been shown in Figure 2, 

 The speed of the water particles is plotted as abscissa and time as 

 ^^e OT'di'-iate. The areas a, b„ c, and c. d, ej, show the distances which 

 the wster particles move forward in the crest ox" the wave and backward 

 in the trou^ of the wave. These areas must be equal in sise, hit 

 the speeds are not the same» Let us imagine that the bottom of 

 the ocean is horizontal and that V-rain is the slowest speed which the 

 water must have to move a partible of a certain weight and size. Then 

 it is obvious that such a particle will be moved forward a distance 

 which is equal to the space f-b-g, and then backward a little, equal to 

 the space h-d-i. As these two spaces are not of the same size (the 

 first one is the largest) the particles will be moved forward a distance 

 which is as long as the difference between the spaces. It follows 

 that if the waves are so large that the speed along the bottom is 

 greater than V-min, the particles of the diirensions mentioned will be 

 moved toward the shore. 



In this connection there must be noted a theory proposed 40 years 

 ago (1898) by the Italian engineer Paolo Cornaglia. The background 

 for Mr. Cornaglia' s theory is the well-known observation that on 

 certain parts of a coast no material is deposited, and if the coast 



