This, it was considered, gave a clew to the
solution of the problem. A pair of barrels was now taken and a
template fitted accurately to the side of the right-hand one. As the
template fitted the barrel when the latter was not subject to internal
pressure, upon such pressure being applied any alterations that might
ensue in the length or contour of the barrel could be duly noted. The
right-hand barrel was then subjected to internal hydrostatic pressure.
The result is shown in an exaggerated form in Fig. 2. It will be seen
that both barrels are bent into an arched form. This would be caused
by the barrel under pressure becoming extended circumferentially, and
thereby reduced in length, because the metal that is required to
supply the increased circumference is taken to some extent from the
length, although the substance of metal in the walls of the barrel by
its expansion contributes also to the increased diameter. A simple
illustration of this effect is supplied by subjecting an India-rubber
tube to internal pressure. Supposing the material to be sufficiently
elastic and the pressure strong enough, the tube would ultimately
assume a spherical form. It is a well known fact that heavy barrels
with light charges give less divergence than light barrels with heavy
charges.
After the above experiments it was hoped that, if a pair of barrels
were put together parallel and soldered only for a space of 3 in.
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