Nebraska advertiser., 1882-02-16
THE STORY OF THE TIDES.

What They Tell Of the Growing Length
of the Day and of the Birth of the
Moon.
From scientific point of view, the
work done by the tides is of unspeaka-
BILE Importance. Whence is this ener-
gy derived with which the tides do their
work. II the tides are caused by the
moon, the energy they possess must
also be derived from the moon. This
looks plain enough, but unfortunately
il is not true. Would il be true to as
sert that the finger of the riiieman
which pulls the trigger supplies the en-
ergy with which the riie-bullet is ami
mated? OF course it would not. The
energy is derived from the explosion
of the gunpowder, and the pulling of
the trigger IL merely the means by
which that energy is liberated. In u
somewhat similar manner the tidal wave
produced by the moon is the means
whereby part of the energy stored in
the earth is compelled to expend itself
in work Let me illustrate this by a
comparison between the earth rotating
on its axis and the fy-wheel of an en-
gine. The fly-wheel is sort of reser-
voir into which the engine pours its
power at each stroke of the piston.
The various machines in tho mill mere
ly draw off the power from the store
accumulated in the tly-wheel The
earth is like gigantic fly-wheel de-
tached from the engine, though still con-
nected with the machines in the mill.
In that mighty fly-wheel stupendous
quantity of energy is stored up, and
stupendous quantity of energy
would be given out before that fly
wheel would come To rest. The
earth's rotation is the reservoir from
whence the tides draw the energy they
require for doing work. Hence it Is
that though the tides are caused by the
moon, yet whenever they require ener-
gy they draw on the supply ready to
hand in the rotation of the earth. The
earth differs from the fly-wheel of the
engine in II very important point As
the energy is withdrawn from the fly
wheel by the machines in the mill, 80 it
is restored thereto by the power of the
steam-engine, and the fly runs uniform
ly. But the earth is merely the fly
wheel without the engine. When the
work done by the tides withdraws ener-
gy from the earth, that energy is never
restored. 1t, therefore, follows that the
earth's rotation must be decreasing.
This leads to consequence of the most
wonderful importance. Ii tells us that
the speed with which the earth rotates
on its axis is diminishing We car
state the result in manner which ha.
the merits of simplicity and brevity
The tides are increasing the length o.
the day. AT present, no doubt, the ef
feet of the tides in changing the length
of the day is very small A day now il
not appreciably longer than u day
hundred years ago. Even in thou
sand years the change in the length OF
the day is only fraction of second
But the importance arises from the fac
that the change, slow though it is, lie
always in one direction. The day
continually increasing. In millions O
years the accumulated effect become
not only appreciable, but even of start
ling magnitude.
The change in the length of the da
must involve "a corresponding change i
the motion of the moon. Ii the moo
acts on the earth, so, conversely, doe
the earth react upon the moon. Tn
earth is tormented by the moon, so
strives to drive away its prosecutor. A
present the moon revolves round tn
earth at distance of about $4,000
miles. The reaction of the earth tend
to increase that distance, and To fore
the moon to revolve in an orbit whic
is continually getting larger and larger
AS thousands of years roll on, tn
length Of the day increases second b
second, and the distance of the moo
increases mile by mile. A million yeal
ago the day, probably, contained som
minutes less than our present day {
twenty-four hours Ourretrospect doe
not halt here: we at once project ou
view back 10 an incredibly remot