you will see the
water copiously charged with sediment which the tide is bearing along.
Engineers are well aware of the potency of the tide as a vehicle for
transporting stupendous quantities of sand or mud. A sand-bank impedes
the navigation of a river; the removal of that sand-bank would be a
task, perhaps, conceivably possible by the use of steam dredges and
other appliances, whereby vast quantities of sand could be raised and
transported to another locality where they would be innocuous. It is
sometimes possible to effect the desired end by applying the power of
the tide. A sea-wall judiciously thrown out will sometimes concentrate
the tide into a much narrower channel. Its daily oscillations will be
accomplished with greater vehemence, and as the tide rushes furiously
backwards and forwards over the obstacle, the incessant action will
gradually remove it, and the impediment to navigation may be cleared
away. Here we actually see the tides performing a piece of definite
and very laborious work, to accomplish which by the more ordinary
agents would be a stupendous task.

In some places the tides are actually harnessed so as to accomplish
useful work. I have read that underneath old London Bridge there used
formerly to be great water-wheels, which were turned by the tide as it
rushed up the river, and turned again, though in the opposite way, by
the ebbing tide. These wheels were, I believe, employed to pump up
water, though it does not seem obvious for what purposes the water
would have been suitable. Indeed in the ebb and flow all round our
coasts there is a potential source of energy which has hitherto been
allowed to run to waste. The tide could be utilized in various ways.
Many of you will remember the floating mills on the Rhine. They are
vessels like paddle steamers anchored in the rapid current. The flow
of the river makes the paddles rotate, and thus the machinery in the
interior is worked. Such craft moored in a rapid tide-way could also
be made to convey the power of the tides into the mechanism of the
mill. Or there is still another method which has been employed, and
which will perhaps have a future before it in those approaching times
when the coal-cellars of England shall be exhausted. Imagine on the
sea-coast a large flat extent which is inundated twice every day by
the tide. Let us build a stout wall round this area, and provide it
with a sluice-gate. Open the gate as the tide rises, and the great
po