they are refined in one furnace and puddled
in another, to effect certain changes in the
iron; the iron, in masses of sixty or seventy
pounds, receives a few mighty thumps from a
shingling hammer weighing five or six tons;
then it is pressed between enormous rollers,
then heated again, and then rolled again to
its proper thickness as sheet-iron.  Like as
dough becomes toughened by good kneading,
does the iron become toughened by these
repeated meltings and beatings, and rollings
and pressings.  And the rivets, too, share
this quality with the sheets, for they are
formed of bar-iron or rod-iron, which has
undergone a similar course of treatment.

The well-kneaded sheets and rivets, as we
have said, take part, in a remarkable degree,
in modern engineering.  Steam-engine boilers
and steam-vessel funnels are examples familiar
to every one.  The sheets are cut to the
proper sizes by shears of most irresistible
persuasion, which sever the material as
effectually and as quietly as the clasp-knife of the
coalheaver severs his bread and cheese into
coalheaver's mouthfulls; another machine
punches rivet holes around the margin of
each sheet, quickly and cleanly; and a third
machine cuts off pieces from a rod of iron to
form tough and sturdy little rivets.  Then,
in order that the flat sheets may acquire a
curvature similar to that of a boiler or a
funnel, they are hammered on an anvil,
a gauge or pattern being used to prevent the
iron from overleaping the bounds of propriety,
and acquiring too great a convexity.  And
now comes the riveting.  The riveter has
a boy at his elbow, which boy is commander-
in-chief over a small portable forge; the
edges of two sheets are lapped one over
another, a rivet is made hot, it is put through
the coinciding holes in the two plates, and
two men batter away at the two ends of the
rivet with huge hammers, until the spreading
ends of the rivet bind with intense pressure
the two plates together.  Thus does the iron
cool, and thus do the rivets succeed each other,
and thus is a boiler or a funnel built up.  It
is hollow, but it is nevertheless strong.

As a rule, keep at least half a mile away
from a boiler factory; for, of all the wild
and bewildering noises presented by
industrial art, nothing approaches in intensity
that which results from thousands of
rivets being hammered by dozens of lusty
arms, day after day.  And yet (as extremes
meet) we would really suggest a visit to a
boiler factory, to see what our Fairbairns
and our Garforths of the busy north have
done towards the silencing of this hullabaloo.
Many may recollect the two riveting
machines which found a place in the Great
Exhibition, but which, unfortunately, could
not be shown in action; the rivets are not
hammered, but the two ends are treated with
such a loving embrace as effectually to bind
the rivet and the two plates together.  There
is a lesson also in the philosophy of "strikes"
afforded by these machines.  Mr. Fairbairn,
in the Official Illustrated Catalogue, gives us
this bit of information: "The invention of
the riveting machine originated in a 'turn-
out' of the boiler-makers in the employ of
the exhibitor about fifteen years ago.  On
that occasion the attempt was made to rivet
two plates together by compressing the red-
hot rivets in the ordinary punching press.
The success of this experiment immediately
led to the construction of the original
machine."  Improvements suggested
themselves from time to time, until, about eight
years ago, the present riveting-machine was
brought to a state of great efficiency.  "The
machine effects by almost instantaneous
pressure what is performed in the ordinary
mode by a long series of impacts.  The
machine fixes in the firmest manner eight
three-quarter-inch rivets in a minute."  And
what is more, the process is a sober, quiet
one, and the riveting is said to be better
effected than by the hammer.

It is to the humble plate-and-rivet that
we owe the magnificent Britannia tubular
bridge—beautiful in an engineering, though
not in an aesthetic sense.  The difficulties
which pressed upon Robert Stephenson in
his attempt to carry the Chester and
Holyhead Railway over the Menai Straits, have
become notorious.  He was required to
make a bridge flat at the bottom, and
rigid enough to support railway trains with
very little flexure.  At the point chosen, the
length of the whole bridge is one thousand
three hundred and fifty feet, or thereabouts;
but the fortunate existence of the Britannia
rock in the middle of the stream, causes the
entire width of the water there, nine hundred
feet and upwards, to be divided into two
spans of about four hundred and fifty feet
each.  These distances were required to be
kept open throughout their whole length, so
that vessels of large size might pass every-
where under the bridge, the bottom part of
which was to be one hundred feet, at least,
above high-water mark.  These rigorous
conditions were a sore puzzle to the engineer;
and after all other kinds of bridge were
considered and abandoned, the plate-and-rivet
principle was thought of.  Then occurred the
remarkable experiments of Mr. Fairbairn and
Mr. Hodgkinson, and the wonderful proofs of
strength which such construction afforded—
sixty-nine thousand six hundred and sixty-
four pounds of pulling force required to
separate plates kept together by a half-inch
rivet!  Then came the cutting up of nearly
six thousand tons of iron into plates, and
seven hundred tons of bars into rivets, and
the fitting of eighty miles of angle-iron, and
the punching of seven million holes for rivets
and bolts, and the gradual building up of
these enormous tubes.  Let it be regarded as
a wonderful evidence of economy of materials,
of strength produced by judicious
arrangement, that this bridge, with its half-inch