breech-plug longitudinally into the barrel. This formed a little anvil
whereon the bullet was to be beaten into the grooves. But the bottom
was flattened, and the powder acted only on the periphery of the ball
instead of the centre, tending thus to give it an oblique direction.

Here Delvigne picked up the weapon for another trial. He accomplished
far the most important advance yet seen--an advance relatively as
great as Watt's separate condenser in the steam-engine. He retained
the _tige_, but he _changed the spherical ball into a cylinder with a
conical point_, as we now have it. In this he, in effect, reached the
ultimatum of progress as regards the general form of the projectile.
He assimilated it to Newton's solid of least resistance. That primeval
missile, the arrow, had for unnumbered centuries presented to the
eyes of men an illustration of a simple truth which scientific formula
succeeded, scarce a couple of centuries since, in evolving. "The
bridge was built," as the old sapper told his commander, "before them
picters" (the engineer's designs) "came." The arrow-head describes, as
it whirls through the air, a solid varying from a cone only so far as
its edges vary from straight lines. This variation serves to blend the
cone with the cylinder formed by the revolution of the arrow-head and
the feather. The difference in length between the ball and the arrow
is due to the necessities of the case. The least practicable length
is best for both. The office of the spirally-wound feather in
communicating a rotary motion, and thereby balancing, by an opposite
force, the tendency of the missile to swerve in any given direction,
is fulfilled by the spiral groove of the rifle. Of course, the
ordinary smooth musket is unfitted to the conico-cylindrical ball.
Discharged from such a barrel, there being nothing to keep the point
in the direction of its flight, it soon tumbles over, like an arrow
without a feather, and strikes wide of the mark.