this hollow time we have altered all that;
our friend plate-and-rivet has wedged in
his hollow principles even here.  Let us look
at the Keyham steam-dock, now in process
of formation at Devonport.  Here is a
basin, the water of which is confined by a gate
eighty-two feet long, thirteen feet wide, and
forty-two feet deep; and although the flood
occasionally presses on one side of this gate, or
caisson, with a force of fourteen hundred tons,
uncompensated by any pressure on the other
side, yet is this barrier as hollow and honey-
combed as the tubular girders and bridges.
Mr. Fairbairn (the presiding genius of this
species of hollowness) has so managed matters
that this caisson will rise and sink, and permit
or obstruct the flow of water with singular
ease.  Plate-and-rivet is the magic agency,
not only to the economy of material, but
to the great furtherance of the purposes
for which the basin is intended.  And that
which is good at Devonport cannot be far
otherwise at Hartlepool, where tubular dock-
gates have just been applied.  The mightily
busy coal people of Hartlepool require enlarged
docks for their increasing trade; and they
have consequently opened recently a new dock
fourteen acres in extent.  The dock is
connected with the harbour or basin at one end,
and with the old dock at the other; and, at
these points of junction, there are lock-gates
fifty or sixty feet across, formed almost
wholly of wrought-iron plates riveted together.
Hollow as they are, they swing on their hinges,
and resist the watery pressure more bravely
than gates formed of ponderous timbers.

The gallant spirit of plate-and-rivet yields
neither to pulling nor pushing, to hanging nor
pressing, to water-impulse nor dry-impulse.
A crane, the well-known instrument for
lifting heavy weights, might reasonably be
expected to present a thorough solidity in
every part; yet Mr. Fairbairn, as if to show
that he can beat every one hollow by every-
thing hollow, now makes his cranes hollow,
and of the very self-same kind of plates and
rivets as he makes his bridges and girders,
and caissons and gates.  Sir David Brewster,
at the meeting of the British Association in
1851, took occasion to speak of these
remarkable cranes in the following terms:—

"These structures indicate some additional
examples of the extension of the tubular
system, and the many advantages which may
yet be derived from a judicious combination of
wrought-iron plates, and a careful distribution
of the material in all those constructions
which require security, rigidity, and strength.
The projection or radius of the jib of these
cranes is thirty-two feet from the centre of
the stem, and its height thirty feet above the
ground. It is entirely composed of wrought-
iron plates, firmly riveted together on the
principle of the upper side being calculated to
resist tension, and the under or concave side—
which embodies the cellular construction—to
resist compression.  The form is correctly
that of the prolonged vertebrae of the bird
from which this machine for raising weights
takes its name; it is truly the neck of the
crane."

One of the cranes, thus built up of mere
sheet-iron, has had as great a weight as
twenty tons (nearly forty-five thousand
pounds) suspended from it without any
fracture or injury.

Wherever we turn, east, west, north, or
south, in the old world and in the new, we
find a determination existing to make a
hollow time of it everywhere.  Bending sheet-
iron into flutes or hollows is the new way of
constructing portable houses—for California,
if you choose to go there.  California?
What! the tubular principle, the Fairbairn
hollowness, the plate-and-rivet, going to
California ?  Even so.  It is now almost as easy
to go to the diggings with an iron house to
your back, as to go to Alabama with a banjo
on your knee.  The Eagle Foundry at
Manchester will tell us all about this corrugated
iron.  In 1849, iron houses for California began
to be made at those works.  One such house
was twenty feet long by ten wide: it
comprised a sitting-room and a bed-room, one
outer and one inner door, and a window to
each room.  The walls and roof were formed
of sheet-iron, only one-eighth of an inch in
thickness, in sheets sixty inches by thirty.
The upright supports were of hollow rolled
iron filled up with wood; the doors had
frames of bar-iron, with panels of sheet-iron,
and the window shutters were similarly
constructed.  Every sheet, and every bit of angle-
iron and T-iron and bolt and rivet, were
numbered, so that three or four men could
put up the house in three or four days; and
thus was a fifty-pound house built in a
Manchester factory in a week, and neatly packed
off ship-wise to the far west.  Another iron
house for California was of loftier pretensions,
—and if it ever come to the hammer of a
Californian auctioneer, he will doubtless describe
it in his advertisements as "a spacious
detached residence, capable of accommodating a
family of distinction"—it was twenty-seven
feet long by twenty-two wide; was two
stories high, and had eight rooms; but still
its walls and roofs were mere sheet-iron.  The
Prince Consort admired, it is said, a little
model iron house at the Great Exhibition, and
forthwith ordered a corrugated ball-room for
Balmoral; that is, a convenient sheet-iron
detached building; which, without provision
as a living room, might be serviceable for balls
and occasional purposes.  This iron pavilion
is about sixty feet long, twenty feet wide,
and seventeen high to the ridge of the roof;
it has cast-iron pilasters (hollow, of course,)
and base plates, two plate-iron doors, eight
French windows, and corrugated sheet-iron
walls and roof.  Perhaps this is the first ball-
room, except one of canvas, which has walls
only one-sixteenth of an inch in thickness;
yet the wind is always busy; and, sometimes,