394 EEPOET — 1891. 



finger over the face, was constracted by Mr. Greensliields, and worked 

 well, proving a great convenience. 



§ lY. — Description of the Experiments on the Movement op Sand 

 IN A Tideway, from September 4, 1890, to August 1891. 



14. JExperiment III., Plan 1, Tanls E and F, Plate V. — These 

 experiments were intended as a repetition of Experiments I. (Second 

 Report, p. 528), which were only continued to 36,000 tides. The only 

 difference in the conditions being that, while in Experiment I. the sand 

 was initially laid up to the top of the river, Section 38, in Experiment III, 

 the sand was only laid up the river to Section 13. These experiments 

 were carried on during the vacation, Mr. Foster kindly keeping the tanks 

 running and reading the counters daily. In this way 47,000 tides were 

 ran in tank E, and 66,000 in F, when the surveys for Plan 1 were taken. 



These surveys show a rather more advanced state than is shown in 

 Plan 2, Experiment I., but they present exactly the same characters. 

 In tank E the sand in the estuary is slightly lower in the longer experi- 

 ment than in the shorter, but shows the same distribution. In both 

 experiments in tank E the level of the sand at the mouth of the river is 

 that of mean tide, and in both experiments the level of the sand reaches 

 the H.W.L. in the generator at Section 11, or 13 miles up from the mouth, 

 and in both the tide continued to rise to the top of the river. 



In tank F, also, both experiments show the same general distribution 

 of sand in the estuaries and river. In the estuary the phenomenon pre- 

 viously observed with a low value for the criterion, namely, the large 

 ripple, is more pronounced in the longer experiment ; bat in both 

 experiments the river has become barred at an early stage, showing that 

 the conditions in F during the formation of the estuary have been below 

 those essential for similarity. 



The rise of tide observed at the end of the Experiment III. in both 

 E and F is below those observed at the earlier stages. In tank E the 

 rise of tide with the same rise in the generator has fallen to 0"125 foot at 

 47° tides, though it was 0-140 foot at 32,000, and 0-095 foot at 60,000 in F, 

 against 0-096 foot at 32,000. This phenomenon, which becomes more 

 pronounced in some of the later experiments, is accounted for by the im- 

 proved tideway as the experiment gets older, allowing the estuary to 

 empty itself more completely. It requires notice, since it renders esti- 

 mates, such as the value of the criterion of similarity based upon the rise 

 of tide, difficult. The same quantity of water passes up and down the 

 estuary, but does not effect the same rise of tide at the generator, which 

 falls as the experiment gets older, while the rise of tide up the estuary 

 increases at the same time. 



15. Experimenfs on Increased Length of Tidal River. Experiments TV., 

 E and F, luitli Land Water, Plates VI., X., and IV., October 22 to 

 November 17, 1890.— The sand laid 0-333 foot in E, and 0-187 in Ffrom 

 Section 13 up the river to Section 26 down the estuary. Mean rise of 

 the tide, 0310 in E, 0'197 in F. Rise of the generators the same as 

 before, periods 33-47 in E, 22-21 in F. 



The conditions were thus the same as in Experiment III., with the 

 exception that the tidal periods were reduced in the ratio 1 to «/2. As 

 i*educed to a 30-foot tide, this would have the effect of increasing the 

 horizontal scales in the ratio v/2 to I. Thus, while in Experiment III. 



