injury inflicted in this way is to be found in the method adopted for
hooping cast iron tubes cast by Rodman's process. If we take into
consideration the undoubted fact of the existence to a considerable
extent of useful initial stresses in these tubes, then the hoops should
be put on them either with very little shrinkage or none at all, whereas
ordnance authorities everywhere have applied to this case methods which
are only correct for tubes which are free from initial stresses.

[Footnote 3: In certain cases this, of course, may be an
advantage, as, for instance, when the inner tube is under
injurious initial stresses; but then, in order to be able to
apply the necessary shrinkage, we must know the magnitude of
these stresses.]

[Illustration: Fig. 2]

During the process of hooping guns it is very important to know how to
take into account the value and mode of distribution of the prejudicial
stresses in the inner tube, should such exist. Knowing these stresses,
it is possible, by regulating the tension of the hoops, to reduce the
compression of the metal at the surface of the bore to the proper
extent, thus doing away with the previously existing tension, and by
that means removing a source of weakness in the tube. In precisely the
same way in the shrinkage of gun hoops attention must be paid to the
character and value of the stresses which arise in the course of their
manufacture; otherwise it will be impossible to hoop the barrel
throughout in a proper manner. If prejudicial stresses exist in the
metal of a hoop before it is put in its place, then, when the gun is
fired, if it had been shrunk on with the degree of tension usually
allowed, the layer situated in the internal radius will be extended