NABORE 
517 
THURSDAY, SEPTEMBER 30, 1886 
OUR GUNS 
WA HEN a careful engineer sets about designing a 
structure, he first determines the strain which the 
several parts of it will have to withstand ; he then selects 
his material and proportions it so that it will be able 
to carry the strains safely ; in determining the margin 
which should be allowed he uses judgment based upon 
his own experience or that of others who have designed 
similar structures ; and if the strains be difficult to deter- 
mine, or if they be of the nature of severe and sudden 
shocks and complicated cross strains he increases his 
margin in proportion. Experience has shown, for ex- 
ample, that wrought iron in the form of a railway bridge 
may be worked safely at a load equal to one-fourth of 
that which will break it down, a cast-iron bridge to one- 
sixth. The builder of a steam-engine rarely loads those 
parts of his machinery which have to endure sudden and 
reverse strains to more than one-eighth or one-tenth of 
their ultimate strength. If his structure fail, the first 
thing the engineer does is to re-calculate his strains and 
the dimensions he has given to the various parts, and if 
these should prove correct he seeks for the cause of 
failure in unlooked-for defects in his material ; and if 
failure in the same class of structure, of various sizes, 
recur repeatedly in the same place, he comes to the con- 
clusion, either that he has under-estimated the strains, or 
that the margin of safety which he has allowed is not 
sufficient. An engineer accustomed to act in this manner 
must look with dismay upon the report of the Committee 
appointed to examine into the cause of the failure of the 
12-inch gun of the Collingwood, and of other guns of 
similar construction. It is possible, of course, that the 
Committee have been able to calculate the strains which 
tend to destroy the guns, and have satisfied themselves 
that sufficient metal has been provided for the purpose ; 
but, if so, it is much to be regretted that they have not 
seen fit to make the results of their investigations public, 
because it would have been instructive to know how the 
stresses are arrived at and what margin of safety is con- 
sidered sufficient for a gun. When Colonel Maitland 
read his paper on our new guns at the United Service 
Institution in the middle of 1884, the strains certainly 
were not known to the Ordnance Committee, because the 
pressure curves, purporting to represent one-fourth of the 
bursting pressure of the guns, and which were given on 
the official drawings, were incompetent to account even 
for the muzzle energy which the shot was supposed to 
possess, and consequently provided nothing whatever for 
other important work which has to be performed during 
the discharge. This fact was pointed out by the Zugineer 
early in 1885, in an article commenting on one of the 
Howard Lectures which had just been delivered at the 
Society of Arts, and the weak point in our guns was 
actually indicated before any failures had taken place ! 
How much has the knowledge of the Ordnance Com- 
mittee advanced in the meantime, and is four still con- 
sidered a sufficient factor of safety ? Any careful engineer 
who reflects on the strains a gun is subjected to would 
certainly class it among steam-engines, subject to the | 
VOL. XxXxXIV.—No, 883 
Toughest work, and not to the class of railway bridges, 
which have well-defined and simple strains to stand. 
What takes place when a gun is discharged? First, 
there is the direct pressure of the gases, which is still 
very imperfectly known. Next, this pressure travels 
along the bore at a very rapid rate, producing.a shearing 
strain between the material in advance of, and in rear of 
the base of the shot, and this strain is intensified at each 
point where a sudden change of thickness takes place. 
Thirdly, there is the reaction to the force producing 
rotation of the shot, which tends to twist the barrel. 
Fourthly, there are the strains produced by the momentary 
presence of a white-hot body pressing against the walls 
of the bore with a pressure ranging from 25 tons to 1 ton 
per square inch; and, lastly, there is the longitudinal 
strain representing the reaction between the pressure on 
the base of the bore and the inertia of the gun itself. 
What engineer would dream of counteracting such strains 
as these with a less margin than eight or ten, if he were 
perfectly unfettered, and if he were certain of the manner 
in which the strains were transmitted through the metal 
of the gun ; but even on this point there are grave doubts, 
for it seems almost certain that the strains travel as pulses 
or vibrations, in a manner which sets at defiance all 
ordinary modes of calculation. No engineer would be 
surprised if guns, with a factor of safety of only four, 
burst frequently. 
But it will, no doubt, be argued that guns of the strength 
suggested would be impracticable. We do not hold that 
opinion, because weight ina gun, even for naval purposes, 
is not objectionable, since the force of recoil diminishes 
with the increase of weight, and the metal appropriated 
to the gun would be saved in the carriage and structure 
of the ship ; while, for land service, weight can be no 
objection whatever. The Committee make no allusion to 
a necessity of keeping down the weight of guns, hence it 
must be supposed that they would not sacrifice safety to 
this end, although it is well known that there is a kind of 
race among gun-makers to produce the greatest amount 
of shot-energy per ton of gun. It seems to us, therefore, 
most unfair that the whole blame of our failures is to rest 
on the Royal Gun Factory, that is, on the quality of 
material and on the manufacture, when it is certain that 
the faults are faults of design—a want of sufficient metal 
—a view which the Committee adopt by their acts, though 
not by their words ; for they are adding largely to the 
weight of the guns in the very parts which experience 
and the investigations of outsiders have proved to be 
deficient in strength. 
But although the Ordnance Committee are reticent as 
to the scientific views which they hold respecting the 
structure of guns, they have a way of taking the public 
into their confidence, through the instrumentality of a 
lecture delivered by one of their body, whose talents as 
an agreeable expounder of popular science are well known, 
and they show much wisdom in making these manifesta- 
tions take the form of lectures instead of papers read 
before scientific Societies. The advantage of a lecture is 
that no awkward questions can be asked, and no fallacies 
or errors pointed out. Thus, when the 7hunderers gun 
burst, Sir Frederick Bramwell delivered a very pleasant 
lecture at the Royal Institution, and the other day the 
same gentleman selected the subject of our guns as the 
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