Washington standard. [volume] (Olympia, Wash. Territory) 1860-1921, 1882-05-26
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? If the tides are caused by the
moon, the energy they possess must
also be derived from the moon. This
looks plain enough, but unfortunately
it is not true. Would it be true to as
sert that the finger of the riheman
which pulls the trigger supplies the en-
ergy with which the rifle-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 is merely the means by
which that energy is liberated. In =
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 fiy-wheel of an en-
gine. The tiy-wheel is sort of reser-
vOir into which the engine pOurs its
power at each stroke of the piston.
The various machines in the mill mere
ly draw off the power from the store
accumulated in the fly-wheel. The
earth is like a gigantic fiy-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
a stupeadous 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 fy-wheel of the
engine in very important point. As
the energy is withdrawn from the fly
wheel by the machines in the mill, so 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 a consequence of the most
wonderful Importance. 1t tells us that
the speed with which the earth rotates
on its axis is diminishing. We can
state the result in a manner which has
the merits of simplicity and brevity.
The tides are increasing the length Of
the day. At present, no doubt, the eff
feet of the tides in changing the length
Of the day is very small. A day now is
not appreciably longer than a day q
hundred years ago. Even in q thou
sand years the change in the length of
the day is only fraction of q second.
But the importance arises from the fact
that the change. slow though it is, lies
always in one direction. The day is
continually increasing. In millions OF
years the accumulated effect becomes
not only appreciable, but even of start
ling magnitude.
The change in the length of the day
must involve corresponding change in
the motion of the moon. If the moon
acts on the earth, SO, conversely, does
the earth react upon the moon. The
earth is tormented by the moon, so it
strives to drive away its prosecutor. At
present the moon revOlves round the
earth at distance of about 100000
miles. The reaction of the earth tends
to increase that distance, and to force
the moon to revOlve in an orbit which
Is continually getting larger and larger.
As thousands of years roll on, the
length of the day increases second by
second. and the distance of the moon
increases mile by mile. A million years
ago the day, probably, contained some
minutes less than our present day of
twenty-four hours. Our retrospect does
not halt here; we at once project our
view back to an incredibly remote
. epoch which was a crisis in the history
OF our system. 1t must have been at
least 5O,OOO,OOO years ago. 1t may
have been very much earlier This
crisis was the interesting occasion
when the moon was born. The
length of the day was only very few
hours. If we call it three hours
we shall not be far from the
truth. Perhaps you may think that if
we booked back to still earlier epoch,
me day would become still less, and
hny hhnally disappear altogether! This is,
however not the case. The day can
never have been much less than three
nours In the present order of things.
Everybody knows that the earth is not
spnere, put there is protuberapce at