self. His plan consisted of a combined attack by sea
and land upon a scale so tremendously formidable, and assisted by such
ingenious inventions of art, that it held out a prospect of certain
success.

After a brief consideration the Court of Madrid announced its
unqualified approval of the scheme, and orders were at once issued for
its adoption. Not only was the reduction of the fort now considered
certain, but so vast were the powers to be employed, and so prodigious
the armament to be brought against the walls, that the annihilation of
every stone upon the rock was not unexpected. The plan embraced two
leading features: first, a bombardment from the isthmus, upon a scale
hitherto unknown; secondly, an attack by sea along the whole length of
the line-wall. For this purpose floating batteries of such construction
that they were to be "at once incombustible and insubmergible," were to
be employed.

Each battery was clad on its fighting side with three successive layers
of squared timber, three feet in thickness; within this wall ran a body
of wet sand, and within that again was a line of cork soaked in water
and calculated to prevent the effects of splinters, the whole being
bound together by strong wooden bolts. To protect the crews from shells
or dropping shot, a hanging roof was contrived, composed of strong
rope-work netting, covered with wet hides, and shelving sufficiently to
prevent the shot from lodging.

Not the least remarkable part of these vessels was a plan for the
prevention of combustion from red-hot shot. A reservoir was placed
beneath the roof from which numerous pipes, like the veins of the human
body, circulated through the sides of the ship, giving a constant supply
of water to every part, and keeping the wood continually saturated.

To form these powerful batteries, ten ships, from six hundred to
fourteen hundred tons burden, were cut down to the proper proportions,
and upward of two hundred thousand cubic feet of timber were used in
their construction. Each battery was armed with from eight to twenty
heavy brass cannon of new manufacture, with a reserve of spare pieces.
The crews varied in number from seven hundred sixty to two hundred fifty
men. One large sail propelled each ship.

Besides this tremendous armament which was to annihilate the line of
defence from the sea, preparations of no less magnitude were being made
for the attack on the northern front. Not fewer than twelve hundred
piec