rred to. A single barrel was now taken, to which a template was
fitted, in order to record its exact length. The barrel was then
subjected to a heavy internal hydrostatic pressure. Under this
treatment it expanded circumferentially and at the same time was
reduced in length. 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. at
the breech end, and were then coupled by two encircling rings joined
together as in Fig. 4, the left-hand ring only being soldered to the
barrel, very accurate shooting would be obtained. For, it was argued,
that by these means the barrel under fire would be able to contract
without affecting or being affected by the other barrel; that on the
right-hand, it will be seen by the illustration, was the one to slide
in its ring.

A pair of able 0.500 bore express rifle barrels were accordingly
fitted in this way. Fig. 3 shows the arrangement with the rings in
position. Upon firing these barrels with ordinary express charges it
was found that the lines of fire from each barrel respectively crossed
each other, the bullet from the right-hand barrel strikin