The Iola register. [volume] (Iola, Allen County, Kansas) 1875-1902, 1882-09-29
The Story Of the Tides.

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 assert
that the finger of the rifleman which
pulls the trigger supplies the energy
with which the rifle bullet is animated?
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 some
what similar manner the tidal wave
produced by the moon is the means
whereby large part of the energy
stored in the earth is compelled to ex-
pend itself in work. Let me illustrate
this by comparison between the earth
rotating on its axis and the fly-wheel of
an engine. The fy-wheel is a sort of
reservoir, into which the engine pours
its power at each stroke of the piston.
The various machines in the mill mere
Iy draw off the power from the store
accumulated in the fly-wheel. The earth
is like a gigantic tiy-wheel detached
from the engine, though still connected
with the machines in the mill. In that
mighty fy-wheel stupendous quantity
of energy is stored up, and a stupen-
dous quantity of energy would be given
out before that fy-wheel would come to
rest. The earth's rotation is the reser-
yoir 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 energy 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 a very impor-
tant point. As the energy is with
drawn from the tly-wheel by the ma
chimes in the mill, so it is restored
thereto by the power of the steamer
CINE, and the fly runs uniformly. But
the earth is merely the tly-wheel with
out the engine. When the work done
by the tides withdraws energy from the
earth, that energy is never restored. 1t
therefore follows that the earth's rota-
ton must be decreasing. This leads to
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 manner which has the merits of
simplicity and brevity. The tides are
increasing the length of the day. At
present no doubt the effect of the tides
in changing the length of the day is
very small. A day now is not appreci-
ably longer than day hundred years
ago. Even in thousand years the
change in the length of the day is only
a fraction of a second. But the i'm
portance arises from the fact that the
change, slow as it is. lies always in one
direction. The day is continually in
creasing. In millions of years the accu-
mulative effect becomes not only ap-
preciable, but even of startling magni-
tude. The change in the length of the
day must involve a corresponding
change in the motion of the moon. If
the moon acts on the earth and retards
the rotation of 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 entire earth at distance of about
two hundred and forty thousand miles.
The reaction of the earth tends to in
crease that distance and to force the
moon to revolve in an orbit which is
continually getting larger and larger.
AS thousands ofyears 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
fifty million years ago. 1t may have
been very much earlier. This crisis was
.ihe interesting occasion when the moon
Eas born. The length of the day was
&nly a very few hours. If we call it
si,ree hours we shall not be far from the
truth. Perhaps you may think that if
We looked back to still earlier period
she day would become still less and
finally disappear altogether! This is,
however, not the case. The day can
never have been much less than three
hours in the present order of things.
Every body knows that the earth is not
sphere, but there is a protuberance at
the Equator, SO that as our school books
tell us, the earth is shaped like an Or
ange. 1t is well known that this pro-
tuberance is due to the rotation of the
earth on its axis, by which the equato-I
rial parts bulge out by centrifugal1
force. The quicker the earth rotates
the greater is the protuberance If,
however, the rate of rotation exceeds
certain limit the equatorial portions of
the earth could no longer cling together.
The attraction which unites them would
be overcome by centrifugal force, and
general break up would occur. 1t can
be shown that the rotation of the earth
when on the point of rupture CORE
spends to length of the day some
where about the critical value of three
hours, which we have already adopted.
1t is, therefore. impossible for US to
suppose day much shorter than three |
hours. Let us leave the earth for few |
minutes and examine the past history
af the moon. We have seen the moon |
revolve around the earth in an ever
orbit, and consequently the |
moon must in ancient times have been
nearer the earth than it is now. No doubt |
the change is slow. There is not much |
1iffprpnce hatween tho orbit IF tho