Evening star. [volume] (Washington, D.C.) 1854-1972, 1882-02-04
THE STORY OF THE TIDES.

u the nay anu Oh the birth OF the
Moon.
Nature.
From scientific point Of view. the work
done by the tides is of unspeakable 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
1t be true to assert that the finger of the rife
man 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 ia merely the means by
which that energy is liberated In q 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 extend itself
IN work. Let me illustrate this by COMPARE
son between the earth rotating on its axis and
the ny wheel of an engine: The fly wheel is q
sort of reservoir, into which the engine pours
its power at each stroke of the piston. The va
rious machines in the mill merely draw off the
power from the store accumulated in the fly
wheel. The earth is like gigantic fly wheel
detached from the engine. though stall con-
nected with the machines in the mill In that
mighty fly wheel stupendous quantity of en-
ergy Is stored up, and stupendous quantity of
energy would be given out before that fly wheel
would come to rest The earths rotation is the
reservoir from whence the tides draw the en-
ergy 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 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energy is withdrawn from the fly wheel by the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 iy runs
uniformly. But the earth is merely The fly
wheel without the engine. When the work
done by the tides .withdraws energy from the
earth, that energy is never restored 1t, there
fore, follows that the earths rotation must be
decreasing. This leads to a consequence Of the
most wonderful Importance. 1t tells us that
the speed with which the earth rotatcs 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 day now is not apprecably longer
than day hundred years ago. Even in a
thousand years the change i'm the length of fine
day is only fraction of second. But the inn
pOrtance arises from the fact that t,e change
slow though it is lies always in one direction.
The day is continually increasing. In millions
or years the accumulated effect becomes not
only appreciate, but even Of startling magni-
tIlde.
The change in the length OF the day must in
volve 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 re-
wolves round the earth at a distance Of about
24O,O miles. The reaction of the earth tends
to Increase that distance. and to force the moon
to revOlVe in an orbit which is continually get
ting 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 dav.
probably. contained some minutes less than our
present day OF twenty-four hours. Our retro
spect does not halt here; we at once project our
view back to an incredibly remote epoch which
was crisis in the history Of our system. 1t
must have been at least 100000 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 looked back to still earlier
epoco. the day would become still less and
finally disappear altogether This is, howe ever.
not the case The day can never have been
much Tess than three hours in the present order
OF things. Everybody knows that the earth is
not sphere. but there is protuberance at the
equator, so that as our school books tell us, the
earth is shaped like an orange. It is we'll known
that this prOtuberance is due to the rotation of
the earth on Its axis by which the equatorial
parts bulge out by centrifugal force. The
quicker the earth rotates the greater is the pro-
tuberance. If, however, the rate of rotation ex-
ceeds certain limit, the equatorial portions of
the earth could no longer cling together The
attraction which unites them would be over
come by centrifugal force, and a general break
up would occur. 1t can be shown that the ro-
tation OF the earth when on the point OF rupture
corresponds to q length of the day somewhere
about the critical value of three hours. which
we have already adopted. 1t is therefore i'm
possible for us to suppose day much shorter
than three hours.
Let US leave the earth for a few minutes and
examine the past history of the moon. We have
seen the moon revOlve around the earth in an
ever 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 much difference between the
orbit OF the moon thousand years ago and the
orbit In which the moon is now moving But
when we rise to millions of years, the difference
becomes very appreciable. Thirty OF forty mill
lions OF years ago the moon was much closer to
the earth than it is at present; very
possibly the moon was then only half its present
distance. We must, however. look still earlier
to q certain epoch not less than fifty million of
years ago. At that epoch the moon must have
been so close to the earth that the two bodies
were almost touching. Everybody knows that the
moon reyOlyes 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 must have been
of years ago the moon completed it's journey i'm
a week. instead of taking twenty eight days, as
at present. Looking back earlier still we find
the month has dwindled down to day, then
down to few hours, until at that wondrous
epoch, when the moon was almost touching the
earth, the moonspun round the earth once every
three hours
In those ancient times see our earth to be a
noble globe, as it is at present. Yet it is not
partly covered with oceans and partly clothed
with verdure. The primeval earth seems rather
fiery and half molten mass, where no organic
life can dwell. Instead Of the atmosphere which
we now have, I see dense mass of vapors in
which, perhaps, all the oceans of the earth are
suspended as clouds. l see. that the sun still
rises and sets to give the succession Of day and
of night, but the day and the night together
only amounted to three hours. instead of twen-
ty-four. Almost touching the chaotic mass of
the earth is another much smaller and equally
Chaotic body. Around the earth see this small
body rapidly rotating The two reyOlve to-
gether, as If they were bound by invisible bands
The smaller body is the moon.
Gymnastic Beans.
new use for beans has been discovered by q
Boston lady, who has gymnasium for girls,
and CureS curvature IF f!a spine nv niIipv hoan