tion as to pull her to pieces--to say nothing of the risk of
having her hull shattered at one fell blow by the explosion of the
steam boiler. These undoubtedly are dangers which have to be provided
against, and probably the occasional lack of care has been the cause
of many an unreported loss, as well as of recorded mishaps from broken
tail-shafts and screws, or from explosions far out at sea.

The air-compressing pendulum will no doubt be constructed on such a
principle that, whenever there is any danger of its weighty movements
getting beyond control or doing any damage to the vessel, its force
can be instantly removed at will, and the apparatus can be brought to
a standstill by the application of friction brakes and other means.
The weight may be made up of comparatively small pigs of iron, which,
through the opening of a valve controlled from the deck by the stem of
the pendulum, can be let fall out into the hold separately. The
swinging framework would then be steadied by the friction brake
gripping it gradually.

Auxiliary machinery of this class can only be made use of, as already
indicated, to a certain strictly limited extent, owing to the tendency
of any swinging weight in a vessel to aggravate the rolling during
heavy weather. Some tentative schemes have been put forward for
tapping a source of wave-power by providing a vessel with flippers,
resting upon the surface of the water outside her hull, and actuating
suitable internal machinery with the object of propulsion. A certain
amount of encouragement has been given by the performances of small
craft fitted in this way; but it is objected by sea-faring men that
the behaviour of a large vessel, encumbered with outlying parts
moving on the waves independently, would probably be very erratic
during a storm and would endanger the safety of the ship itself. No
kind of floating appendage, moving independently of the vessel, could
exercise any actual force by the uprising of a wave in lifting it
without being to some extent sunk in the water; and, accordingly, when
the waves were running high there would be imminent risk that heavy
volumes of water would get upon the apparatus and prevent the ship
from righting itself. Many of the schemes that have been put forward,
by patent and otherwise, for the automatic propulsion of ships have
entirely failed to commend themselves by reason of their taking little
or no account of the behaviour of a ship, fitted with the propo