descent, four blocks of lead, weighing fifty pounds, are slung
over his shoulders; and a water-proof bag containing a hammer, a chisel,
and a dirk-knife is fastened over his breast.

He is transferred from the steamer that has brought him from the city to
a small boat, which is rowed to a spot over the wreck, and a short iron
ladder is put over the side, down which he steps; and when the last rung
is reached, he lets go, and the water bubbles and sparkles over his head
as he sinks deeper and deeper.

The immersion of the diver is more thrilling to a spectator than it is
to him. The rubber coil attached to his helmet at one end is attached at
the other to an air-pump, which sends him all the breath he needs, and
if the supply is irregular, a pull at the cord by his right hand secures
its adjustment. He is not timid, and he knows that the only thing he has
to guard against is nervousness, by which he might lose his presence of
mind. The fish dart away from him at a motion of his hand, and even a
shark is terrified by the apparition of his strange globular helmet. He
is careful not to approach the wreck too suddenly, as the tangled
rigging and splinters might twist or break the air-pipe and signal line;
when his feet touch the bottom, he looks behind, before, and above him
before he advances an inch.

Looming up before him like a phantom in the foggy light is the ship; and
now, perhaps, if any of the crew have gone down with her, the diver
feels a momentary horror; but if no one has been lost, he sets about his
work, and hums a cheerful tune.

It may be that the vessel has settled low in the sand, that she is
broken in two, or that the hole in her bottom can not be repaired. But
we will suppose that the circumstances are favorable, that the sand is
firm, and the hull in an easy position.

The diver signals to be hauled up, makes his report, and in his next
descent he is accompanied by several others, who help him to drag
massive chains of iron underneath the ship, at the bow, at the stern,
and in the middle. This is a tedious and exhausting operation, which
sometimes takes many days; and when it is completed, the pontoons are
towed into position at each side of the ship.

The pontoons, simply described, are hollow floats. They are oblong,
built of wood, and possess great buoyancy. Some of them are over a
hundred feet long, eighteen feet wide, and fourteen feet deep; but their
size, and the number of them used, depend