36 
NATURE 
| Vou. 9, 1882 
a a ee eee eee 
Now if we consider the case of any one coil, such as 
that at the position K, we see that when the gun is com- 
pleted it is under considerable compression, but whilst the 
construction is proceeding, when the coil at this point is 
being laid on, it is laid on under ¢exszon, which tension is 
reduced by every successive additional coil until it 
attains the state of compression shown in the diagram of | 
the finished structure. The question therefore to be 
solved is this, What is the proper tension for putting on 
the coil at K, so that when all the other coils are put on, it 
may be in the required state of compression? This 
problem must be solved for every individual coil. This | 
having been done, each coil is laid on by automatic 
machinery with its proper tension, and the final result is 
that shown in the diagram. 
When the full internal pressure of the explosion 
operates, the result is as follows :—Every coil is brought 
up to the same tension simultaneously and exerts the | 
same resistance per square inch of section throughout the 
whole thickness of the gun as denoted by the line Ho. 
Fic. 
The ultimate strength therefore of such a gun increases 
in the simple ratio of the number of coils, a result not 
attainable by any other mode of construction, and this is 
the first advantage over the hoop system. The second 
is, that there is no fear of error through inaccurate work- 
manship or unequal shrinkage. The tensions of the wire 
coils are actually measured by the machine by which they 
are laid on, instead of being zxferred from presumed 
accuracy of workmanship or uniform shrinking power of 
the material. In the next place there is no danger from 
| latent defects. The wire is not subject to such defects as 
thick hoops are, and can moreover be easily tested before 
it isapplied. Then again the process of construction is 
simple and expeditious, it is the substitution of accurate 
| automatic machinery for very highly skilled labour. 
Beyond this it is much less costly, for although the wire 
itself costs a high price per ton as compared with the 
raw material used in the hoops of the Woolwich guns, yet 
when the labour and work in the latter is taken into 
account, it will be found that it largely exceeds that of 
I. 
the wire gun ton for ton, and as was before pointed out, | 
the wire gun of equal strength can be made very much 
lighter. 
In a paper read before the Institution of Civil Engineers 
in 1879 the writer estimated the cost of a muzzle- 
loading 20-inch gun weighing 150 tons, constructed on 
the wire principle, at £5,041, or £33 16s. per ton. We 
believe that the price paid by Government to Sir Wm. | 
Armstrong for the 1o00-ton guns produced from his firm 
was £16,000 each, or £160 per ton. 
We now proceed to the question of longitudinal strength. 
In the old guns, as well as the present Woolwich guns, 
the Armstrong, Whitworth, and Krupp guns, the longi- 
tudinal strain between the breech and the trunnions is | 
borne by the chase of the gun itself, that is to say, that 
the same material which kas to resist the enormous cir- 
cumferential strain has at the same time to resist a very | 
intense longitudinal strain. Now it has been generaily | 
maintained that although this is very large in the gross, | 
yet when it is divided by the sectional arm of the chase, | 
it is comparatively small per square inch of section. This | 
is a very great mistake as was pointed out several years 
ago by the late Sir William Palliser. The fact is, that 
this strain is no more uniformly divided over the sectional 
area of the chase than is the circumferential strain between 
the inner and outer circumferences. 
Sir Wm. Palliser devised a method of breech construc- 
tion which has since been adopted at Woolwich, by means 
of which the longitudinal strain is much more equally 
distributed, and since then the accident of a breech blow- 
| ing out has been comparatively rare, and we believe has 
| never occurred in Sir Wm. Palliser’s own guns. 
It has 
always been a difficulty with many people to understand 
how the breech is to be secured in a wire gun. It is 
obvious that the coils of wire afford no longitudinal 
strength, and the general idea has been that it was there- 
fore necessary to resist the whole longitudinal strain by 
the inner tube. . 
The writer has always maintained that no real diffi- 
culty exists, and that the connection between the breech 
and the trunnions should be by means of material quite 
independent of and placed outside of the coils of wire. 
