more
intermittent in its action than the windmill--excepting perhaps in a
very few localities where there is a cloudless sky throughout the
year. The windmill gathers up the power generated by the expansion of
the air in passing over long stretches of heated ground, while a solar
engine cannot command more of the sun's heat than that which falls
upon the reflector or condenser of the engine itself. The latter
machine may possibly have a place assigned to it in the industrial
economy of the future, but the sum total of the power which it will
furnish must always be an insignificant fraction.

The wave-power machine, when allied to electric transmission, will,
without doubt, supply in a cheap and convenient form a material
proportion of the energy required during the twentieth century for
industrial purposes. Easy and effective transmission is a _sine qua
non_ in this case, just as it is in the utilisation of waterfalls
situated far from the busy mart and factory. Hardly any natural source
of power presents so near an approach to constancy as the ocean
billows. Shakespeare takes as his emblem of perpetual motion the
dancing "waves o' th' sea".

But the ocean coasts--where alone natural wave-power is constant--are
exactly the localities at which, as a rule, it is the least
practicable to build up a manufacturing trade. Commerce needs smooth
water for the havens offered to its ships, and inasmuch as this
requirement is vastly more imperative during the early stages of
civilisation than cheap power, the drift of manufacturing centres has
been all towards the calm harbours and away from the ocean coasts. But
electrical transmission in this connection abolishes space, and can
bring to the service of man the power of the thundering wave just as
it can that of the roaring torrent or waterfall.

The simplest form of wave-motor may be suggested by the force exerted
by a ferry boat or dinghy tied up to a pier. The pull exerted by the
rope is equal to the inertia of the boat as it falls into the trough
of each wave successively, and the amount of strain involved in rough
weather may be estimated from the thickness of the rope that is
generally found necessary for the security of even very small craft
indeed. A similar suggestion is conveyed by the need for elaborate
"fenders" to break the force of the shock when a barge is lying
alongside of a steamer, or when any other vessel is ranging along a
pier or jetty.

A buoy of larg