e a replica of the mail-boat of to-day. The
opposition presented by the water to the passage of a vessel increases
by leaps and bounds as soon as the rate now adopted by the cargo
steamer is passed, and thus presents a natural barrier beyond which it
will not be economically feasible to advance much further.

If then we recognise clearly that steam cargo transport across the
ocean can only be done remuneratively at about one half the speed now
attained by the very fastest mail-boats, we shall soon perceive also
that the chances of the auxiliary principle, if wisely introduced,
placing the "sailer" on a level with the cargo ship worked by steam
alone, are by no means hopeless. A type of vessel which can be trusted
to make some ten or twelve knots regularly, and which can also take
advantage of the power of the wind whenever it is in its favour, must
inevitably possess a material advantage over the steam cargo slave in
economy of working, while making almost the same average passages as
its rival.

Then, also, the sailless cargo slave, in the keen competition that
must arise, will be fitted with such appliances as human ingenuity can
in future devise, or has already tentatively suggested, for invoking
the aid of natural powers in order to supplement the steam-engine and
effect a saving in fuel. One of these will no doubt be the adoption of
the heavy pendulum with universal joint movement in a special hold of
the vessel so connected with an air-compression plant that its
movements may continually work to fill a reservoir of air at a high
pressure. The marine engines of the ordinary type will then be
adapted to work with compressed air, and the true steam-engine itself
will be used for operating an air compressor on the system adopted in
mines.

The pendulum apparatus, of course, is really a device for enabling a
vessel to derive, from the power of the waves which raise her and roll
her, an impetus in the desired direction of her course. Inventions of
this description will at first be only very cautiously and partially
adopted, because if there is one thing which the master mariner fears
more than another it is any heavy moving weight in the hold, the
motions of which during a storm might possibly become uncontrollable.
When steam was first applied to the propulsion of ships the common
argument against it was that any machine worked by steam and having
sufficient power to propel a vessel would also develop so much
vibra