r bombardment of the piston by steam or the gases of
combustion runs his engines and propels his cars. The first man who
wanted to kill another from a safe distance threw the stone by his arm's
strength. David added to his arm the centrifugal force of a sling when
he slew Goliath. The Romans improved on this by concentrating in a
catapult the strength of a score of slaves and casting stone cannon
balls to the top of the city wall. But finally man got closer to
nature's secret and discovered that by loosing a swarm of gaseous
molecules he could throw his projectile seventy-five miles and then by
the same force burst it into flying fragments. There is no smaller
projectile than the atom unless our belligerent chemists can find a way
of using the electron stream of the cathode ray. But this so far has
figured only in the pages of our scientific romancers and has not yet
appeared on the battlefield. If, however, man could tap the reservoir of
sub-atomic energy he need do no more work and would make no more war,
for unlimited powers of construction and destruction would be at his
command. The forces of the infinitesimal are infinite.

The reason why a gas is so active is because it is so egoistic.
Psychologically interpreted, a gas consists of particles having the
utmost aversion to one another. Each tries to get as far away from every
other as it can. There is no cohesive force; no attractive impulse;
nothing to draw them together except the all too feeble power of
gravitation. The hotter they get the more they try to disperse and so
the gas expands. The gas represents the extreme of individualism as
steel represents the extreme of collectivism. The combination of the two
works wonders. A hot gas in a steel cylinder is the most powerful agency
known to man, and by means of it he accomplishes his greatest
achievements in peace or war time.

The projectile is thrown from the gun by the expansive force of the
gases released from the powder and when it reaches its destination it is
blown to pieces by the same force. This is the end of it if it is a
shell of the old-fashioned sort, for the gases of combustion mingle
harmlessly with the air of which they are normal constituents. But if it
is a poison gas shell each molecule as it is released goes off straight
into the air with a speed twice that of the cannon ball and carries
death with it. A man may be hit by a heavy piece of lead or iron and
still survive, but an unweighable a