haped like a water
tortoise, and managed by a single person. It contained sufficient air to
support respiration thirty minutes without being replenished, valves to
admit or reject water for the purpose of rising or sinking, ballast to
keep it upright, and a seat for the operator. Above the rudder was a
place for carrying a large powder magazine, constructed from two pieces
of oak timber, and capable of carrying one hundred and fifty pounds of
powder, with the apparatus for firing it. Within the magazine was an
apparatus constructed to run any proposed length of time under twelve
hours, after which it sprung a strong lock similar to that of a gun,
which gave fire to the powder. This apparatus was so secured that it
could be set in motion only by the casting off of the magazine from the
vessel.

"With this machine a skilful operator could swim so low on the surface
of the water, as to approach at night very near to a ship without being
discovered. After sinking quickly, he could keep at any necessary depth,
and row to a great distance in any direction, without coming to the
surface. Bushnell found, however, that much trial and instruction were
required for a man of common ingenuity to become a skilful manager. It
was first tried by his brother, who, unfortunately, was taken ill at the
time when he had become an able operator. Another person was procured,
and the first experiment tried upon the Eagle, a sixty-four, which Lord
Howe commanded in person. He went under the ship, and attempted to fix
the wooden screw into her bottom, but struck, as was supposed, a bar
of iron running from the rudder-hinge. Not being well skilled in the
management of the machine, he lost the ship in attempting to move to
another place; and, after seeking her in vain for some time, rowed a
little distance and rose to the surface. Daylight had now advanced so
that the attempt could not be renewed, and, fearing he was discovered,
he detached the magazine from his vessel and escaped. In an hour the
powder exploded, throwing a vast column of water to an amazing height,
and leaving the enemy to conjecture whether it was caused by a bomb, a
water-spout, or an earthquake. Want of resources obliged Mr. Bushnell to
abandon his schemes for that time; but, in 1777, he made an attempt from
a whale-boat against the Cerberus frigate, by drawing a machine against
her side with a line. It accidentally became attached to a schooner and
exploded, tearing the vesse