strengthened determined. The stresses which arise in a hollow cylinder
when it is formed of several layers forced on one upon another, with a
definite amount of shrinkage, we call the stress of built-up cylinders,
in order to distinguish them from natural stresses developed in
homogeneous masses, and which vary in character according to the
conditions of treatment which the metal has undergone. If we conceive a
hollow cylinder made up of a great number of very thin layers--for
instance, of wire wound on with a definite tension--in which case the
inner layer would represent the bore of the gun, then the distribution
of the internal stresses and their magnitude would very nearly approach
the ideally perfect useful stresses which should exist in a homogeneous
cylinder; but in hollow cylinders built up of two, three, and four
layers of great thickness, there would be a considerable deviation from
the conditions which should be aimed at.

The magnitude of the stresses in built-up cylinders is determined by
calculation, on the presumption that initial stresses do not exist in
the respective layers of the tube and of the hoops which make up the
walls of the cylinder. Nevertheless, Rodman, as early as the year 1857,
first drew attention to the fact that when metal is cast and then
cooled, under certain conditions, internal stresses are necessarily
developed; and these considerations led him, in the manufacture of cast
iron guns, to cool the bore with water and to heat the outside of the
moulds after casting. Although Rodman's method was adopted everywhere,
yet up to the present time no experiments of importance have been made
with the view of investigating the internal stresses which he had drawn
attention to, and in the transition from cast iron to steel guns the
question has been persistently shelved, and has only very lately
attracted serious attention. With the aid of the accepted theory
relating to the internal stresses in the metal of hooped guns, we can