ft tide first, it will be seen that if the float started with
the current it would travel twelve miles in the tide; three and
a half from twelve leaves eight and a half miles. A vertical line
dropped from the intersection of the eight miles and a half line
with the curve of the current gives the time two hours and a half
before the end, or four hours after the start of the current at which
the discharge of the sewage must cease at the outfall in order that
the rear part of the column can reach the required point before
the current turns. As on this tide high water is about fifteen
minutes after the current, the latest time for the two hours of
discharge must be from one hour and three-quarters to three
hours and three-quarters after high water. Similarly with the
12 ft tide having a total travel of four miles: three and a
half from four leaves half a mile, and a vertical line from the
half-mile intersection gives one hour and three-quarters after
the start of the current as the time for discharge to cease.
High water is two hours and a quarter after the current;
therefore the latest time for the period of discharge would be
from two hours and a half to half an hour before high water,
but, as during the first quarter of an hour the movement of the
current, though slight, would be in the opposite direction, it
would be advisable to curtail the time of discharge, and say
that it should be limited to between two hours and a quarter
and half an hour before high water. It is obvious that if
sewage is discharged about two hours after high water the
current will be nearing its maximum speed, but it will only
have about three hours to run before it turns; so that,
although the sewage may be removed with the maximum rapidity
from the vicinity of the sea outfall, it will not be carried to
any very great distance, and, of course, the greater the