ost probably be made available for assisting in the propulsion of
sailing ships which are not furnished with machinery of any type
suitable for the driving of a screw. A very much simplified form of
the pendulous or rocking weight is applicable in this case. A
considerable amount of cargo is stowed away in an inner hull, taking
the shape of what is practically a gigantic cradle rocking upon
semicircular lines of railway iron laid down in the form of ribs of
the ship. To the sides of these large rocking receptacles are
connected the rods carrying, at their other ends, the pistons of large
force-pumps which draw the water in at one stroke and force it out to
sternwards, below the water line, at the other.

In this arrangement it is obvious that only the "roll" and not the
"pitch" of the vessel can be utilised as the medium through which to
obtain propulsive force. But it is probable that fully eighty per
cent. of the movements of a vessel during a long voyage--as indicated,
say, by the direction and sweep of its mast-heads--consists of the
roll. Each ton of goods moved through a vertical distance of one foot
in relation to the hull of the vessel, has in it the potentiality of
developing, when fourteen or fifteen movements occur per minute, about
one horse-power. A cradle containing 200 tons, as may therefore be
imagined, can be made to afford very material assistance in helping
forward a sailing ship during a calm. In such tantalising weather the
"ground-swell" of the ocean usually carries past a becalmed vessel
more waste energy than is ever utilised by its sails in the briskest
and most propitious breeze.

For sailing ships especially, the rocking form of wave-motor as an aid
to propulsion will be recommended on account of the fact that when the
weather is "on the beam" both of its sources of power can be kept in
full use. The sailing vessel must tack at any rate with the object of
giving its sail power a fair chance, and thus, when it has not a fair
"wind that follows free," it must always seek to get the breeze on its
beam, and therefore usually the swell must be taking it sideways. It
would be only on rare occasions that a sailing vessel, if furnished
with rocking gear for using the wave-power, would be set to go nearer
to the teeth of the wind than she would under present conditions of
using sail-power alone. The advantage of the wave-power, however,
would be seen mainly during the calm and desultory weather which