constructed with all the skill, science, and experience which engineers
and artillerists can command, and therefore it would seem that instances
of defective strength should not arise. Such cases, however, do occur
everywhere, and irresistibly give rise to the suspicion that not only is
the system of construction of guns of large caliber faulty, but also
that the conditions of their manufacture must be considered as
defective. Bearing in mind the enormous sums of money expended by every
nation in order to secure an armament of completely trustworthy guns,
this question demands speedy and searching investigation. The first step
in this direction is the study of the internal stresses inherent in the
metal; because, if such exist, and are capable of attaining, under
certain conditions, considerable magnitudes, then it is absolutely
necessary to take advantage of them in order to increase the resistance
of the metal, instead of allowing them to act to its detriment.

The study of natural internal stresses is of importance, not only with
reference to gun making, but also in respect of other structures where
great resistance is required. All have heard of the sudden failure of
crank shafts and piston rods, of the bursting of boiler shells and
tubes, of the breaking of tires, etc. In the majority of cases the
investigations into the causes of such sudden failures have not led to
any definite results. It has usually been found that the metal possessed
a satisfactory elastic resistance, and satisfied all the conditions set
down in the specifications. Had attention been paid during these
investigations to the state of the internal stresses in the metal, the
cause of unlooked-for accidents might have been explained, and steps
would consequently have been taken to avoid them in future.

We are also familiar with the development of considerable internal
stresses in various kinds of steel articles which are subjected to