ON THE ACTION OF WAVES AND CL'RUKMS. 393 



while above these limits the applicability of the simple hydrokinetic law 

 to these experiments has been abundantly verified in models varying in 

 scale from six inches to a mile to an inch and a half to the mile, and with 

 vertical exaggerations, as compared with a 80-foot tide, ranging from 60 

 to 100. 



The laws of the distribution of the sand in a tideway under circum- 

 stances of progressing complexity have been determined and have been 

 verified, not only by repetitions of the same experiment but also by pro- 

 ducing similar distributions under different circumstances, which circum- 

 stances, however, conformed to the laws of hydrokinetic similarity. 

 Thus the distributions of sand in simple rectangular estuaries, V-shaped 

 estuaries, and V-shaped estuaries with a long tidal river, have all been 

 investigated and found to be definite. 



Investigations have also been made with definite results of the separate 

 effects of land water in moderate quantities, and of the length of the 

 tidal river on the depth of water in the river and estuary, and of the 

 effect of bold irregularities in the configuration of the lateral boundaries 

 of the estuaries, also of training walls in deep water. And, lastly, the 

 comparative rates and ultimate action of uniform tides and tide varying 

 from spring to neap have been determined. 



It thus appears that this system of investigation has been tested over 

 a great portion of the ground it is likely to cover, and that most of the 

 difficulties that are likely to occur have been met and the necessary pre- 

 cautions found. 



It would seem, therefore, by carefully observing these precautions, the 

 method may now be applied with confidence to practical problems. 



§ III.— The Appar.vius. 



11. General Woi-ling of the Apparatus. — All the apparatus has worked 

 well, although certain repairs have been rendered necessary by wear ; thiis, 

 the motor has required new pins, not much, considering it has made over 

 200 million revolutions. The knife edges, on which the generator of the 

 large tank rests, which are of cast-iron, and 2 inches long, and each carry 

 about 1,000 lb., were found to have, after one million oscillations, worn 

 down ^ of an inch, until they had become so locked in the Vs as to stop 

 the motor. 



12. The viodificatioiis in the Tanks have this year been confined to the 

 introduction of ti-aining walls and groins. These have been made of paper 

 saturated with solid paraSin (which gradually became warped by the 

 pressure), sheet ziuc, and sheet lead or wood, as was most convenient. In 

 the last experiment the large tank was modified by taking out the parti- 

 tion boards and stopping the opening at the end so as to reproduce the 

 original rectangular tank A. 



13. Gearing for the Spifing and Neap Tides, Plate II. — This arrangement, 

 designed by Mr. Greenshields, accomplished the result very neatly and 

 effectually with a minimum of new appliances. It admits of any degree 

 of adjustment in the ratio of maximum and minimum tides, and works 

 easily and well. 



On commencing the work with spring and neap tides it was found 

 essential to have an indicator of the phase of the tide, which would be 

 easily visible without having to examine the gearing. For this a counter, 

 having twenty-nine teeth in the escapement wheel, which carried a long 



