of resistance with the largest quantity of
materials."

The result of the inquiry was the determination
which is now being followed out to
construct for the great harbour in Dover
Bay a breakwater upon the second principle,
that of the upright wall. This does not
convert the deep sea undulations into breakers.
General Sir Harry Jones observed with
interest how the same sea rose and fell without
violence against the upright circular head of
the eastern arm of Kingston breakwater,
while on the long-slope it was breaking with
great fury. Sir H. De la Beche noticed the
same effects produced by the varying nature
of the shore near Fishguard. The same on-
shore sea, which produced a mere flop on the
vertical cliffs, caused heavy rolling breakers
on the beaches. Professor Airey has testified
that he once rowed out of Swansea Harbour
at high water when very high sea was
running, and without risk even of the boat's
touching, passed so near a pier-head that it
could be struck with an oar. Two hundred
yards farther on, he passed a shoal, where
the sea broke so heavily that it carried two
rowers out of the boat and nearly filled it.
The summit of the upright wall breakwater
is exposed to the broken crests of the deep
water waves; but, as we have seen, these are
not dangerous. This, therefore, is the form
of breakwater advocated by the greater
number of the men of science in our day. Its
only drawback, as a sea wall, is the necessity
of building on a bottom levelled by help of
the diving bell, with none but best materials,
facing throughout with heavy blocks well
jointed and cemented. It is liable to wreck
from bad workmanship or fault in the
foundation, and it is a costly structure.

Floating breakwaters have been
condemned so generally for their insecurity;
that, although they do meet one of the great
obstacles to good harbour construction and
allow free passage to the tidal streams, so
keeping the bottom clear of silt, they have
few friends.

The process of silting is the ruin of most
harbours. Here and there, as at Kingston,
blue sea water comes in so free from deposit,
that there is no settlement inside; but
generally the waves and currents keep a
considerable mass of matter in suspension, and
with this the water comes into the closed
harbour, whether protected by a long-slope
or an upright breakwater, to stand and settle.
Our artificial harbours are now mud-traps.
All the cinque ports have been choked in
course of time. It is the shutting out of that
strong movement in the water which stirs up
the muddy sand into its mass that causes
the deposit.  In the Royal George, after it
had been for some time submerged, General
Pasley found little or no accumulation in the
free water about its sides; but inside where
the water had been harboured and stilled, it
was silted up twenty-nine feet.  Thus it is
found that a bay is sandy and shallow;
but a headland round which currents sweep,
is steep.

Dover Refuge Harbour is to be a close
harbour on a grand scale, enclosing by
upright-wall breakwaters a space of seven
hundred acres. Only a weak tidal current will
come in through the narrow entrances from a
sea charged highly with matter whenever
the weather becomes boisterous.  It is
calculated that the deposit within the harbour
will reduce the depth throughout by six
inches annually.  But the yearly cost of
removing those six inches of deposit would be
twenty thousand pounds. Either this cost
must be incurred, or in the long course of time
the Refuge Harbour must needs go the way
of the old cinque ports. In Ramsgate
Harbour, with an area of forty-two acres, the
yearly deposit is two feet in depth. At
Folkestone, with an area of fourteen acres,
the silting is not less. Again, such break-
waters act like groynes upon the outer sea,
and cause an advance of coast, as at Lowestoft,
where the shore, north-eastward of the
harbour, has advanced outwards from the
heel to nearly the line of the head of the wall,
a distance of about five hundred feet. The
approach to Grimsby dock is to be maintained
only at a great annual cost. The Harbour
of Refuge Commissioners accepted the fact in
a sort of despair, that from the stilled water
in harbours sediment must fall to the bottom.
Plymouth breakwater has cost a million and
a half, Cherbourg three millions.

Captain Vetch said in his Dover evidence,
"I have been led to form a strong opinion
that none of our existing modes of construction
are commendable or advisable, and that
if anything is to be done, we must look to
new contrivances and discoveries, all of which
will require to be tested by satisfactory
experiments before adoption."

One of these new contrivances is that of
Mr Calver.  Briefly, it is a stretch of paling
which he calls the Wave Screen—of material
and structure duly considered with regard to
strength and durability, crossing the tide-
way as nearly as possible so as freely to admit
the tide, and to reduce the waves one half
while breaking their crests.  A twelve foot
wave would thus pass through the paling as
a six foot wave into the harbour, and become
further stilled in proportion to the expanse;
but there would still be the scour of the
currents and the stir of the water to keep
the harbour's bed clean, and the hold silt in
suspension. The general idea is not
absolutely new. Sir John Rennie, says Mr.
Calver, seemed almost to be describing the
wave screen, when in allusion to the moles
of Porto Giulio and Misenum, and the
ports of Astium, Astia, and Ancona, he
remarked: "They were all constructed on
arches, and their object was to produce
sufficient circulatiion of currents through the
arches, and at the same time to have sufficient