, but as these were the directions in
which the wind least frequently blew it might safely be reckoned that
not one-eighth of the possible working hours of a swivel-windmill were
really lost in the fixed machine.

With the type adapted to the working of a dynamo as already described,
it will, in most cases, be convenient to construct two spirals on
uprights set in three holes in the ground, forming lines at right
angles to each other, but both engaging, by suitable gearing, with the
electric current generator situated at the angle. This will be found
cheaper than to go to the expense of constructing the mill on a swivel
so that it may follow the direction of the wind. At the same time it
should be noticed that the adoption of the high speed wind-wheel,
consisting of some kind of spiral on a very long axis, may be made
effective for improving even the swivel windmill itself, so as to
adapt it for electric generation and conservation of power through the
medium of the storage battery. Supposing that a number of small
oblique sails be set upon an axis lying in the direction of the wind,
the popular conception of the result of such an arrangement is that
the foremost sails would render those behind it almost, if not
entirely, useless.

The analogy followed in reaching this conclusion is that of the sails
of a ship, but, as applied to wind-motors, it is quite misleading,
because not more than one-third or one-fourth of the energy of the
wind is expended upon the oblique sails of an ordinary wind-wheel.
Moreover, in the case of a number of such wheels set on a long axis,
one behind the other as described, the space within which the shelter
of the front sail is operative to keep the wind from driving the next
one is exceedingly minute.

The elasticity of the air and its frictional inertia when running in
the form of wind cause the current to proceed on its course after a
very slight check, which in point of time is momentary and in its
effects almost infinitesimal. This being the case, and the principal
expense attendant upon the construction of ordinary wind-engines being
due to the need for providing a large diameter of wind-wheel, with all
the attendant complications required to secure such a wheel from
risk, it is obvious that as soon as the long axis and the very short
sail, or the metallic spiral, have been generally introduced as
adjuncts to the dynamo storage battery, an era of cheaper wind-motors
will have been en