ON THE ACTION OF WAVES AND CURRENTS. 19 PA33 
as in VIII., but was mainly confined to the channels; and, although the 
experiment was continued to 57,000 tides, the condition of equilibrinm 
was far from being arrived at owing to the setting of the sand. After 
the last survey a small stream of land water (one pint per minute) was 
admitted at the top of the estuary without any perceivable effect for 1,000 
tides, wherenpon the experiment was stopped. 
Hzperiment V., B, Plan 1, Plate IV., November 21 to December 2.— 
This was the corresponding experiment in B to Experiment VIII. in A, 
the rise of tide being one-half inch (:042 foot), and the period 50 seconds, 
exaggeration 32. The characteristics were yet more definitely marked, 
rippling being entirely absent, and the action being entirely confined to 
the space between Sections 14 and 18. 
Experiment VI, B, December 5 to December 9.—In this experiment the 
conditions were exactly the same as in Experiment V., B, except that 
the sand, instead of being laid level, was laid with a slope of 1 in 124, 
the slope corresponding to the theoretical condition of equilibrium as in 
the previous experiment. After 6,757 tides with a mean period of 60°1 
seconds the sand was not moved anywhere in the slightest degree. 
Bzperiment VII., B., Plans 1 and 2, Plate V., December 9 to January 
3.—This was a continuation of Experiment VI., with the tidal period 
diminished in the ratio 1 to »/2 from 50 to 35°35, 
The effect of changing the period would be to increase the vertical 
exaggeration, so that the slope of 1 in 124 would not be the theoretical 
mean slope of equilibrium as previously determined, which would be 
1 in 87, so that any sensitiveness to the condition of equilibrium would 
be shown by the shifting up of the sand. 
This commenced at once and continued until the mean slope was 
about 1 in 100 above Section 13. 
The absolute quiescence of the sand in Experiment VI., B, when laid 
with the mean slope of equilibrium corresponding to the period, together 
with the increase of the slope with the increase of period in Experiment 
VII, B, indicates that, although, as shown in Experiment V., the 
limiting conditions under which the water could redistribute the sand 
from the level condition had been long passed, the conditions of 
equilibrium remained the same; or, in other words, that for a half-inch 
tide, with a period of 50 seconds—i.e., an exaggeration of 32—with 
the sand originally distributed, according to the theoretical slope of 
equilibrium, the sand will be in equilibrium, while if the sand be laid 
with a smaller slope the water will shift it, tending to institute the slope 
of equilibrium. 
25. Rectangular Estuaries with Land Water. Experiments X., A, and 
VIL, B, Plate VI., January 7 to March 10.—The conditions in Tank A 
were the same as in Hxperiment V., Plan 1. The sand lay 0°25 foot 
deep, height of mean tide 0°256, rise 0:176, tidal period 50:2 seconds. 
A tin saucer was placed on the sand under Section 1 in’ the middle of 
the estuary, and a stream of water (one quart per minute, about 1 in 170 
the tidal capacity of the estuary per tide) run into the pan. 
During the early distribution of the sand the land water produced no 
apparent effect, but as the sand approached a condition of equilibrium 
the effect of the fresh water in keeping a channel full of water at low 
tide from the source all down the estuary was very marked. The effect 
of this river in distributing the sand at the top of the estuary was also 
marked. The channel did not remain in one place; it gradually shifted 
