72 
NATURE 
[Mov. 24, 1870 

coiled. When that is completed, it is removed from 
before the furnace, the reel or core taken out, and the coil 
allowed to cool. Afterwards it is heated in a reverbe- 
ratory furnace, and welded together by blows on the 
ends from a steam-hammer ; the edges of the coiled bar 
are melting from heat, and therefore unite when thus for- 
cibly pressed on each other, so that it forms a complete 
hollow cylinder or tube of wrought-iron, the fibre going 
round the circumference. The rough surfaces are after- 
wards turned off in powerful lathes. These coils are made 
of various sizes, and several of them are required for each 
gun. They are shrunk on, that is, the outer ones are not 
quite large enough to go over the inner ones, but are 
heated, and when thus expanded are placed over their 
smaller brethren, whom, as they cool, they clasp in a tight 
embrace. Thus all the coils are in a state of tension 
inwards, and this was supposed to increase their power 
of resisting the shock of the discharge which came from 
within outwards. However, this theory very decidedly 
admits of question. Even a little observation seem suffi- 
cient to show that anything in a state of tension is thereby 
weakened to resist a shock in any direction. A shock 
produces a kind of undulation or vibratory action, so that 
its effect returns back in the direction in which it was 
imparted. In Sir Joseph Whitworth’s guns the hoops 
were made accurately to fit each other, so that no shrink- 
ing was required ; but a little shrinkage, we believe, was 
used to ensure close fitting. It will be seen further on that 
this question of the advisability of shrinkage does not 
apply to the guns now made for the British service. 
Hitherto we have only spoken of coils, which, though a 
main part and distinctive feature of the Armstrong gun 
are not the whole of it. A gun made altogether of coils 
would lack strength in resisting the longitudinal strain, or 
tendency of the discharge to tear out the breech endways, 
and this would be an awkward event for the gunners, if 
the gun fired, so to speak, at both ends. To prevent this, 
Sir William Armstrong had a large forged piece of iron, 
like a great cap, placed on the breech end of the inner 
tube and under the coils. The fibres of this, running lon- 
gitudinally, made it.strong in that direction, and guarded 
against a catastrophe so much to be dreaded. This, how- 
ever, was a large forging, and therefore very expensive ; and, 
also, while it strengthened the gun longitudinally, it weakened 
it transversely, by taking up the space nearest the bore 
where the greatest part of the strain was sustained, and 
filling it with iron whose fibres were in the direction of 
the bore instead of around it, as those of the coils. It is 
easy to see how much this took from the power of the 
coils to resist the lateral, transverse, or bursting strain of 
the discharge. The force which the expanding gas exerts 
on the material of the gun must necessarily be inversely 
as the square of the distance from the centre of the 
bore. A coil removed from the tube by the thickness of 
the forged breech-piece cannot resist the full strain of the 
explosion nearly so effectively as if it came at once round 
the tube. Its strength is applied at a disadvantage re- 
presented by the ratio of the square of the radius of the 
coil round the forged breech-piece to the square of the 
radius of a coil round the inner tube. 
Besides, there is another large forging in the Armstrong 
gun, the trunnion-piece, which is placed round the middle, 
and carries the trunnions or short arms by which the gun 
rests on its carriage. 
An Armstrong gun may be thus summed up. (The 
section of a 600-pounder is shown in Fig. 1 as an example.) 
First there is a tube of steel (A) ; this metal is always 
used for the inner part, as its hardness and closeness of 
grain make it better adapted for the rifling—the grooves 
would be quickly worn by the friction of the studs of the 
shot in softer metal—and also better to resist the action 
of the violently expanding gas of the exploding charge of 
powder. All attempts to make the inner tube of coils were 
unsuccessful ; the gas at its enormous pressure searched 

out and took advantage of the most microscopic flaws. 
Next comes the large forged breech-piece behind the steel 
tube, and extending some distance along it. Then come 
the coils (in 5 sets, B, C,D, E, F), shrunk on one over 
another. And lastly, the trunnion piece round the middle. 
The Armstrong gun, as described in our former paper, 
was the pattern on which all our guns were made for the 
British service till 1866, when very important changes, 
which had been proposed by R. S. Fraser, member of the 
Institute for Civil Engineers, and Deputy-Assistant- 
Superintendent of the Royal Gun Factories, after a pro- 
longed series of trials, were approved and adopted by 
Government. This gentleman, not long before, introduced 
intothe manufacture of ordnance acheaper, and, at the same 
time, a better kind of wrought-iron than that before used, 
and he has imported into the construction of the Arm- 
strong gun very considerable modifications, by which 
the country is provided with a stronger gun, one-third 
cheaper, and more quickly made. 
These are three very important items of improvement ; 
viz. strength, cheapness, and rapidity, because simplicity, 
of manufacture. The saving effected is from 35 to 40 per 
cent. on the vast sums expended on heavy ordnance. Most 
of our readers have heard of the Fraser gun, but few, per- 
haps, know where or how it differs from the original Arm- 
strong gun, although all our heavy ordnance is now made 
on this pattern. The information, therefore, may be not 
uninteresting, and a comparison of Fig. 2 with Fig. 1 will 
help to make the difference clearer. Instead of the forged 
breech-piece, the many small coils, and the forged 
trunnion-piece that form the Armstrong gun over the 
inner steel tube, Mr. Fraser uses one immense coil, of 
which the trunnions are part, and which is closed behind 
the tube by a large screw forming the cascable, and 
which is the only forging used in his gun. This will 
show at once how the economy is effected. Both the 
large forgings of the Armstrong gun, the breech-piece, 
and the trunnion-piece are got rid of ; and instead of 
having many coils to be turned, and have their inner and 
outer surfaces reduced, upon which labour and time were 
expended, in addition to the waste of metal, there are only 
the two surfaces of the one great coil to be turned. In 
the 600-pounder, on the old principle, there were sixteen 
coils, and twice that number of surfaces, each representing 
labour and loss. For these reasons also the guns may be 
made much more quickly. This isa very important advan- 
tage, as in an emergency the country could be more quickly 
armed. Strength is also gained to resist the transverse 
strain in two ways, because the coiled iron comes next the 
steel tube, where the forged breech-piece used to come 
formerly, and so the coils are applied at greater advantage, 
and secondly, because the one thick coil is stronger than 
several thin coils, just as a triple deal is stronger than 
three inch deals, And further, the gun is stronger to resist 
the longitudinal strains, because the breech and trun- 
nions are all of one piece, and so the force of the discharge 
upon the gun acts through the trunnions on the carriage, 
and has not, as in the old pattern, a tendency to destroy 
it by tearing one piece or part of the gun from another. 
It is converted from a longitudinal bursting strain into 
recoil. 
It only remains to describe how this immense coil, 
which is the marked feature of the Fraser gun, is made. 
A long and thick bar, much thicker than the one used in 
the Armstrong pattern, is heated and coiled in the manner 
before described. When this has cooled, another bar, 
somewhat longer, is coiled upon it in an opposite direc- 
tion, that is, if the first coils go from right to left, the 
second go over them from left to right, just as the boa 
constrictor overlaps his coils on the prey which he is 
crushing. And then a third bar is coiled in the same 
direction as the first. The whole is then heated in a large 
reverberatory furnace, and a few blows from a powerful 
hammer weld them into a thoroughly combined mass. ; 
