Hunt — On the Action of Waves on 8ea-beaches, S^c. 255 



cliff to water margin, and the distance from water margin to the 

 plunging line, were measured at five equi-distant points, viz. at the 

 two sides of the tank, at the centre, and at the two intermediate 

 points, with the following result, viz. : — 



In this experiment the waves were furnished with a cliff of soft 

 sand to work on, and formed their own beach and along-shore bot- 

 tom, which, as in nature, was a comparatively flat one. 



Subsequently I made some special experiments, to ascertain the 

 point of plunging relative to the point of furthest reach of waves 

 breaking on a beach. A large roofing slate, with parallel lines 

 ruled across it one inch apart, was employed. 



This slate being laid on the artificial beach, with one of the cross 

 lines coincident with the margin of the water, enabled the ob- 

 server to see at a glance how many inches " seaward " of the margin 

 of repose the waves plunged, and how many inches shoreward of 

 the same margin they reached. One particular line was always used 

 for marking the water-level, and was distinguished by the letters 

 W. L. From this line the remainder were numbered 1, 2, 3 ... , 

 in each direction. In an experiment made in February, 1883, the 

 highest reach of the waves, as defined by a row of light chips 

 washed on to the slate, was just under three inches above the water- 

 line, whilst the line of plunging (rapidly scratched on the slate 

 during the progress of the experiment) was over eight inches below 

 the water line. The slope of the slate was not measured. 



On a subsequent occasion the experiment was repeated, with the 

 slate inclined at an angle of 6 degrees, and with waves at the rate 

 of 98 per minute. In this case the waves plunged about eight 

 inches short of the margin of repose, whilst their furthest reach was 

 about five inches beyond it. In both these experiments the line of 



