observation taken at high water one day is not directly
comparable with one taken an hour after high water the next
day, and while perhaps relatively the greatest amount of
information can be gleaned from a series of observations taken
at the same state of the tide, but on tides of differing
heights, still, every observation tells its own story and
serves a useful purpose.

Deep floats and surface floats should be used concurrently to
show the effect of the wind, the direction and force of which
should be noted. If it appears that with an on-shore wind
floating particles would drift to the shore, screening will be
necessary before the sewage is discharged. The floats should be
followed as long as possible, but at least until the turn of
the current--that is to say, a float put in at or near high
water should be followed until the current has turned at or
near low water, and one put in at low water should be followed
until after high water. In all references to low water the
height of the tide given is that of the preceding high water.

The time at which the current turns relative to high and low
water at any place will be found to vary with the height of the
tide, and all the information obtained on this point should be
plotted on squared paper as shown on Fig. 10, which represents
the result of observations taken near the estuary of a large
river where the conditions would be somewhat different from
those holding in the open sea. The vertical lines represent the
time before high or low water at which the current turned, and
the horizontal lines the height of the tide, but the data will,
of course, vary in different localities.