ical
distance of say eight feet, about once in twelve hours, the waves of
the ocean will perform the same work during moderate weather once in
every twelve or fifteen seconds. It is true that the moon in its
attraction of the sea-water produces a vastly greater sum total of
effect than the wind does in raising the surface-waves, but reckoning
only that part of the ocean energy which might conceivably be made
available for service it is safe to calculate that the waves offer
between two and three thousand times as much opportunity for the
capture of natural power and its application to useful work as the
tides could ever present. In no other form is the energy of the wind
brought forward in so small a compass or in so concrete a form. A
steam-ship of 10,000 tons gross weight which rises and falls ten times
per minute through an average height of 3.3 feet is thereby subjected
to an influence equal to 22,400 horse-power. In this estimate the unit
of the horse-power which has been adopted is Watt's arbitrary standard
of "33,000 foot pounds per minute". The work done in raising the
vessel referred to is equal to ten horse-power multiplied by the
number of pounds in a ton, or, in other words, 22,400 horse-power, as
stated.

Wind-power, again, has been to a large extent neglected since the
advent of the steam-engine. The mightiest work carried out in any
European country in the early part of the present century was that
which the Dutch people most efficiently performed in the draining of
their reclaimed land by means of scores of windmills erected along
their seaboard. Even to the present day there are no examples of the
direct employment of the power of the wind which can be placed in
comparison with those still to be found on the coasts of Holland. But,
unfortunately for the last generation of windmill builders, the
intermittent character of the power to which they had to trust
completely condemned it when placed in competition with the handy and
always convenient steam-engine. The wind bloweth "where it listeth,"
but only at such times and seasons as it listeth, and its vagaries do
not suit an employer whose wages list is mounting up whether he has
his men fully occupied or not. The storage of power was the great
thing needful to enable the windmill to hold its own. The electrical
storage battery, compressed air, and other agencies which will be
referred to later on, have now supplied this want of the windmill
builder, bu