The Bolivar bulletin. [volume] (Bolivar, Hardeman County, Tenn.) 1865-1888, 1882-09-28
The Story OF the Tide..


From scientific point Of view the
work done by the tides is Of unspeak-
able IMPORTANCE. Whence is this energy
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 assert
that the finger of the rifieman which
pulls the trigger supplies the energy
with which the rifle bullet is an 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 mdahs by which
that energy Is liberated. In a 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 Ia work. Let me illustrate
this by d comparison between the earth
r5tating on its axis and the i5-wheel Of
an engine. The fy-wheel is a sort of
reservoir, into which the engine Dours
its power at each stroke of the piston.
The various machines in the mill mere
~ draw of the power from the store
accumu ated in the fly-wheel. The ear
is like a gigantic fy-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 fiy-whesl would come to
rest The earth's rotation is the feser-
Foir 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 fly-wheel by the ma
chimes in the mill, so it is restored
thereto by the power of the steam-en~
CINE, and the lily runs uniformly. But
the earth is merely the hy-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-
Con 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 IT'S 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 a hundred years
| ago Even in thousand years the
| change in the length of the day is only
a fraction of a second. But the inn
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-
probable, but even of startling magni-
! tude. The change in the length of the
day must involve corresponding
change in the motion of the moon. Ii
| 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
]
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 Girls, s was
/ the interesting occasion when the moon
was born. The length of the day was
only a very few hours. If we call il
| three hours we shall not be far from the
/ truth. Perhaps you may think that if
we looked back to a still earlier period
the 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.
/ Everybody knows that the earth is not a
| 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 eluato-
rial parts bulge out by centrifugal
force. The quicker the earth rotates
the greater is the protuberance. If,
! however, the rate of rotation exceeds &
certain limit the equatorial portions Ol
the earth could no longer cling together.
The attraction which unites them would
be overcome by centrifugal force, and a
general break up would occur. 1t can
be shown that the rotation of the earth
when on the point of rupture CORE
spends to a length of the day some
| Hxrbn a. hn of h~n
hours, which we have already adopted.
1t is, therefore, impossible for us tC
| suppose a day mucl shorter than three
hours Let us leave the earth for few
minutes and examine the past history
/ of the moon. We have seen the moon
| revOlve around the earth in an evcl
widening 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 mu h
difference between the orbit of the
moon a thousand years ago and the or
bit in VIII. CHI the moon is now moving.
But when we rise to mill Ons of years
| the difference becomes very apprecia-
BILE. Thirty or forty m lions of year.
ago the moon was much closer to tho
sibly the moon was then only half its
present distance. We must, however
look stu earl r, to certain epoch not
less than fifty m Tons Of years ago. Al
that epoch the moon must have been sc
close to the eacth that the two bod es
We're almost touching Everybody
knows that the moon reYolves now
around the earth in period of twenty.
seven days. The period depends upon
the distance between the earth and the
moon. In earlier times the month mus
have been shorter than our present
month. Some m lions of years ago the
moon completed its journey in a week
rNF l.