336 EEPORT— 1889. 



after it had run 17,289 additional tides a partial survey was again taken 

 and plotted in dotted lines on the plan showing Survey IV. 



The dotted contours show a slight change, chiefly in the retreat of the 

 low-water contour up the estuary, and a change in the distribution of the 

 sand at the head of the estuary. These changes, however, are very slight 

 compared with the great difference presented between Plan IV. and all 

 the previous plans. In Plan IV. the contour '004 lies between sections 

 6 and 11, while in Plan III. it lies between 12 and 13, which shows an 

 increase from 1 to 1'47 in the general slope. The low-tide channel on the 

 left has also increased in magnitude and length, extending nearly across 

 the head of the estuary. 



Experiment 6 (tank A), August 28. — In this experiment the initial 

 conditions aimed at were precisely the same as in Experiment 5. 



The sand which had been removed was returned, and all the sand well 

 washed in the tank and then placed as before, the float having been 

 examined and straightened on a surface plate. 



After the sand was laid the water in the tank was brought as near as 

 possible to the level of the sand, and was allowed to stand for twelve 

 hours, when it was found that the sand looked drier on the right side 

 than on the left. The generator was then raised by turning the pinion 

 which, in the position the crank was, would raise the generator about 

 •008 of an inch for one revolution ; this, considering the surface of water 

 exposed, would raise the water '005 inch, in which way it was found that 

 the sand was something like '01 of an inch higher on the right all along 

 the tank. 



The model was then started at the same speed as in Experiment 5, and 

 the development carefully watched. In all respects it appeared to be the 

 same as in the previous experiment, and the daily observations showed 

 the same rate of progress ; not only did the sand gauges and the descent 

 of the sand agree, but the surface of the sand presented the same general 

 appearance. The experiment was stopped after 8,686 tides, before it had 

 reached the stage of the first survey, Experiment 5, go no survey was 

 taken. 



Experiment 1 (Tank B). August 5. — In starting this experiment it 

 was intended that the circumstances should be in every respect homologous 

 to those of Experiment 5 (tank A). 



The sand was introduced in the same way, and brought to the same 

 figure. The tank was started with a period of 365 seconds, that of 

 A having been 53 seconds, which numbers are as the square roots of the 

 dimensions of the tanks. The progressive appearances accorded identically 

 with those noted in tank A, except in one apparently minor particular. 

 And for the first 1,200 tides the downward progress of the sand was 

 nearly the same (a trifle less). 



About this stage an appearance presented itself which had not been 

 noticed in the previous experiment. The arrangement of the sand ap- 

 peared to show a greater rate of downward progression at the middle 

 of the tank towards the generator than at the sides, and this was followed 

 by a somewhat more rapid descent of the lower edge of the sand, which 

 after 5,000 tides began to accumulate in the generator, from which about 

 seven pounds was removed. 



From this stage the lower end of the tank B differed considerably 

 from that of tank A in the same stage. At the upper end the appearances 

 were almost identical, and the reading of the sand gauges agreed well. 



