so that, among the several parts of the one piece
of metal, unequal forces are exerted, and the
whole suffers a strain in its texture by which it
is the more likely to be burst. It happens, also,
that the iron guns, cast formerly in one piece and
then bored, cooling and contracting first upon
the surface, and last in the centre, became in the
centre least contracted; that is to say, had least
power of bearing tension where the greatest
tension was to be applied. This great defect is
partly met by the new practice of casting hollow
guns, and has been most completely recognised
in the plan instituted by Captain Rodman, of
the American service. That gentleman not
only established the casting of guns hollow, but
after they were cast, maintained the outside heat
by fires, and caused the contraction to begin on
the inside by passing a stream of cold water
sixty times the weight of the casting, night and
day for three whole days, through the core of the
gun. A solid and a hollow eight-inch gun, both run
from the same furnace, and made from the same
metal, being tested, one burst at the seventy-third
discharge, the other endured one thousand five
hundred discharges, and then did not burst.

Now, therefore, says theory, instead of casting
a gun in one piece of metal, build it so as that
the stretching power of its inmost part shall
exceed the utmost strain of gunpowder explosion,
and see that the stretching power of each layer
of its substance, counted from within outwards,
shall diminish in exact proportion to the
diminution of the strain. Then when the gun is
fired, the tearing force will be the same at every
point throughout its substance. Artillery so
made, if there were no joints in it to be rent
asunder, could not burst. But how to make it
so, is one question; and how far it is worth
while to make it so, is another.

There was independent application, with full
recognition of the theory, by Captain Blakely
and others, at the time when Mr. Longridge,
working it out for himself, produced what he
thought to be its best solution. Around an
inner tube he tells us to wind coils of wire.
The stretching power of wire is to be calculated
easily, and the use of it can be regulated by
machinery. In the Armstrong gun, and others, the
same end is sought by the use of hoops: each, set
in its place while hot, and compressing that
below it as it cools. Mr. Longridge argues that
the gradation or stretching power is, in the
substance of guns, contracted from hoop to hoop
by abrupt jumps, but that in his wire coils it
may be made to follow the desired curve more
exactly. It is urged by others that, after a
time, rings will be loosened by the frequent
shock of discharges; while against Mr.
Longridge's wire coils, it is urged especially that
they do not protect the breech, but that the
guns as he would construct them, have the
breech so clumsily attached that it may be too
easily blown off. His wire also, if there be one
break in it, may be uncoiled by the explosion. Of
course, also, in assertion or denial of the power of
adjusting properly the tensile power of successive
rings or coils of wire, all shades of opinion appear.

And if it can be done, what then? The tide
of fashion is now strong against cast-iron
artillery, but even cast-iron artillery has doughty
supporters. Some speak of it as if it were glass,
and would have us understand that the cast-iron
guns are habitually blowing themselves up. An
artillery officer rises and says that he has had
twenty years' experience, and has not yet seen a
gun burst. Sir Charles Fox thinks that the best
guns will be those made of iron mixed with some
other metals, such as wolfram and titanium, so
as to ensure the greatest strength and density.
Much again is to be urged on behalf of the great
elasticity of steel. A steel gun cast in one mass
by Mr. Krupp at Essen in Prussia, has been
tested in this country and found almost impossible
to be burst. The Prussian rifled field guns
are now all made of cast steel, with every
expectation that they will equal the guns built in
France or England. As for the old gun metal
(an alloy of copper and tin), that is now becoming
altogether obsolete; but the chemist to the
War Department avers that a far superior metal,
and one that might have come into use but for
the great recent improvements in the construction
of field guns, is made by adding to copper
two or four per cent. of phosphorus.

Not only the gun and its powder, but the
shot used, must be well considered in relation to
the great question of strength. The shot of
the ordinary unrifled service gun is round, as
everybody knows, and does not fit tightly to the
barrel. It runs home to its place easily in loading,
and that would be a great advantage, say
in a sea fight. It is easily projected, but, of
course, with windage, does not perfectly pen up
the gases of explosion till it leaves the muzzle,
and is therefore less liable to be accessory to
any bursting of the gun. But for the same
reason it requires almost double allowance of
gunpowder, and it is less certain of aim: because
the course it takes, will be determined by its
parting touch upon one side or other of the
muzzle. Again, though it leaves the cannon's
mouth more swiftly than any of the close fitting
projectiles, its force is sooner spent; in other
words, its range is more confined. And it is not
even universally admitted that the gun suffers
less damage from a shot that beats against the
sides as it runs out, than from powder that
explodes behind a tightly fitted shot.

It is possible to fit a new-fashioned
projectile to this old-fashioned gun. Mr. Britten
has one method, and Mr. Haddan has two
methods, of converting service guns. But these
gentlemen stand forward with others in the
debate among engineers, civil and military,
opened by Mr. Longridge's account of his
applied theory. It was a learned and practical
debate, summed up by the president's statement
of the fact that we are in the year eighteen sixty
"before anything has been realised in the true
science and practice of gunnery, although,
thanks to Whitworth and Armstrong, the
mechanical department is fast approaching perfection."
We seem to be upon the verge of getting
exact practical knowledge, but we really do not