g the target
10 in. to the left of the bull's eye, while the left barrel placed its
projectile a similar distance in the opposite direction; or, as would
be technically said, the barrels crossed 20 in. at 100 yards, the
latter distance being the range at which the experiment was made.
These last results have been accounted for in the following manner:
The two barrels were rigidly joined for a space of 3 in., and for that
distance they would behave in a manner similar to that illustrated in
Fig. 2, and were they not coupled at the muzzles by the connecting
rings they would shoot very wide, the charges taking diverging
courses. When the connecting rings are fitted on, the barrel not being
fired will remain practically straight, and, as it is coupled to the
barrel being fired by the rings, the muzzle of the latter will be
restrained from pointing outward.

The result will be as shown in an exaggerated manner by the dotted
lines on the right barrel in Fig. 3.

It would appear from these experiments that when very accurate
shooting is required at long ranges with double-barreled rifles, they
should be mounted in a manner similar to that adopted in the
manufacture of the Nordenfelt machine gun, in which weapon the barrels
are fitted into a plate at the extreme breech end, the muzzles
projecting through holes bored to receive them in a metal plate. No
unequal expansion would then take place, and the barrels would be free
to become shorter independently of each other. We give the above
experiments on the authority of their author, who, we believe, has
taken great pains to render them as exhaustive as possible, so far as
they go.--_Engineering._

* * * * *

BALL TURNING MACHINE.

The distinguishing feature in the ball turning machine shown opposite
is that the tool is stationary, while the work revolves in two
directions simultaneously. In the case of an ordinary spherical
object, such as brass clack ball, the casting is made from a perfect
pattern having two small caps or shanks, in which the centers are also
marked to avoid centering by hand. It is fixed in the machine between
two centers carried on a face plate or chuck, with which they revolve.
One of these centers, when the machine is in motion, receives a
continuous rotary motion about its axis from a wormwheel, D. This is
driven by a worm, C, carried on a shaft at the back of the chuck, and
driven itself by a wormwheel, B, whi