who could be assembled and placed under arms at a few days'
notice. This kind of defense would also prove a delusion, for a
hundred acres of soldiers armed with rifles and field artillery would
be powerless to drive away even the smallest ironclad or stop a single
projectile from one. In fact, neither of these plans, nor both
together, would be much more effective than the windmills and
proclamations which Irving humorously describes as the means adopted
by the early Dutch governors of New York to defend that city against
the Swedes and Yankees.

Having considered some of the means of defense that will _not_ answer
the purpose, we may inquire what means _will be_ effective. And here
it should be noted that our defenses should be so effective as not
only to be reasonably safe, but to be so recognized by all nations,
and thus discourage, if not actually prevent, an attack upon our
coast.

In the first place, we must have heavy guns in such numbers and of
such sizes as to overmatch those of any fleet likely to attack us.
These guns must be securely mounted, so as to be worked with facility
and accuracy, and they must be protected from the enemy's projectiles
at least as securely as his guns are from ours. Merely placing
ourselves on equal terms with the enemy, as in case of a duel or an
ancient knight's tournament, will not answer, first, because such a
state of things would invite rather than discourage attack, and
secondly, because the enemy would have vastly more to gain by success
and vastly less to lose by failure than we would. This can be
accomplished much easier than is generally supposed, either by earthen
parapets of sufficient thickness or by iron turrets or casements. It
is evident that the weight of metal used in these structures may be
vastly greater than could be carried on shipboard. Great weight of
metal is no objection on land, but, aside from its cost, is a positive
advantage. This is evident when we consider the enormous quantity of
energy stored in the larger projectiles moving at high velocities. For
example, we often hear of the sixteen inch rifle whose projectile
weighs about one ton, and this enormous mass projected at a velocity
of 2,000 feet per second would have a kinetic energy of 60,000 foot
tons, or it would strike a blow equal to that of ten locomotives of 50
tons each running at 60 miles an hour and striking a solid wall. Any
structure designed to resist such ponderous blows must, therefo