ON THE ACTIOK OF WAVES AND CURRENTS. 



Table I. 



341 



mean distances of the contours measured in miles, from "which the curve of 

 reduced mean slopes shown in fig. 2, Plate II., have been plotted. 



Considering the character of the investigation, the agreement between 

 the slopes is quite as close as could be expected, and there is nothing to 

 argue from the divergences except that the effect of the bottom resist- 

 ances has here been too small to affect the results. 



The Length of the Foreshore. — The interval between mean high and 

 low water, about 12-5 miles according to the kinetic scale for a 30-feet tide, 

 cannot readily be compared with any actual case, since there are no sandy 

 foreshores subject to a 30-feet tideway except those which are in a sea- 

 way and subject to longitudinal currents, while in the deep bays and mouths 

 of estuaries, slopes are cut up with low-water channels besides a want 

 of regularity in the lateral boundaries. In such bays as Morecambe Bay, 

 Lynn deeps, and Sol way Frith, the mean distance from the shore to the foot 

 of the sands at low water must be 8 or 10 miles, and even taking this as 

 the actual length it leaves no great margin for the resistance of the bottom, 

 which would be 50 or 100 times greater in the actual case than with a 

 model with a distortion of 50 or 100 times. 



The only divergences of importance occur at the top and bottom of 

 the slopes. That at the bottom of the curve for Experiment 5 A, Plan 1, 

 is probably owing to the proximity of the generator, as in this plan the 

 survey was continued to the end of the pan. 



Such results, with regard to low- water channels, as have been obtained 

 from the experiments already made are not discussed in this report, 

 because they have been incidental to the immediate purpose of the experi- 

 ments ; they have, however, been carefully recorded for future reference. 

 The same might be said of the manner of action of the water on the sand, 

 were it not that these experiments have revealed a part taken by one of 

 these actions, the importance of which docs not appear to have been 

 hitherto observed. This is the action known as rippling of the sand. In 

 these experiments this action is seen to play an essential part in deter- 

 mining the rate at which the distribution of the sand is effected, while 

 the result of this action— the ripple marks — forms a most conspicuous 

 feature in the final distribution, as seen on the plans, as well as at all 

 preceding stages. 



The ripple marks on the strands are too well known to need descrip- 



