The sun., 1895-05-26
THE STORY OF TIE MOON.
TIE CTRCUMsrA vCEs or IT'S BIRTH,
WHAT IT mas DONE, AND rs DOING.
Professor or Astronomy and Goouastry
at CnrbridEo Untvsrsity, England, snd
Formerly Royal Astronomer OF IRELAND.

Related by Sir Robert Bail, Lownasa n,
Professor or Astronomy and Geomstry
at Cnu,bridEo Untvsrsity. England, ens
Formerly Royal Astronomer OF IRELAND
do not think there Is any chapter in modern
pcienco more remarkable than that which here
propose to describe. II has indeed all the ele
ments OF a romance. am 10 sketch an event
OF the very greatest moment in the history o
this universe, which occurred at period Of the
most extreme antiquity and has been discovered
In tho most remarkable manner.
Tho period OF which write Is far more an
Client than that Of the pyramids OF Egypt, or OF
any other monuments erected by human effort.
II is even more early than that very remote
time, hundreds of thousands Of years ago, when
man himself first came upon this globe. Our ret
respect has to pierce right through those vast
ly protracted cycles which the geologists have
opened up to US. We speak of period long an
terror to the ages during which our continents
were being sculptured into their present noun
tain chains and river courses. We have to look
through those periods, still earlier, when great
animals, now long extinct, fourished on this
earth. The time Of which write is more re-
mote than that very remarkable epoch In earth
history during which the great coal forests
hourished. 1t is earlier than the supreme mo-
ment, countless millions of years ago, when
living organisms first became inhabitants Of
must not stop. We have yet once more to look
back through certain anterior periods TO q time
when our earth was In its earliest youth. The
chapter of history about which write is in
deed In the very dawn of things terrestrial.
1t might be thought that 1t would be utterly
impossible for us to learn anything with regard
70 what took place ut a time 30 immeasurably
anterior to oil sources of tradition, and indeed
to all the ordinary channels for obtaining
knowledge by observation. 1t however fortu-
hatcly happens that the darkness of this early
period is illumined by bright and steady source
of light which will never deceive us IL only we
will follow it properly. Our trustworthy guide
Is to DO the pen of the mathematician, for it is
well known that, unless we are going to dispute
the fundamental proposition that two and two
make four, we cannot impugn the truths which
mathematics disclose. This science knows no
boundaries of space. It recognizes no limits in
time. 1t is ever ready for discussing operations
which take place either in the millionth part of
a second or in the-lapse of uncounted millions
of centurics. Tho processes of mathematics
are alike available for tracing out the delicate
movements in the interior of q molecule not
one-millionth part OF the size Of grain of sand
or for investigating the properties of space 30
vast that the whole solar system occupies only
an inconsiderable point by comparison. Let us,
therefore, see what this infallible guide has to
teach us about that momentous epoch In the
history Of our system when the moon was born.
Our argument proceeds from an extremely
simple and familiar matter. Every one who
has ever been on the seashore knows the daily
ebb and flow of the waters which we call the
tides. Long ere the true nature of the forces
by which the moon acts upon the sea was under
stood. the fact that there was connection be-
tween the.tides and the moon had become GER
fainlvsknOwn Indeed the dni ilv ohse inn Of
q fisherman or any one whose business was con-
cerned with the great deep would have taught
him that the time of high water and the time of
full moon stood at each place In a certain def
mite relation. The fisherman might not have
understood the precise influence Of the moon
upon tho tides, but II he had observed, as he
might in some places, that when the moon was
full tho tide was high at 10 O'Clock in the
morning, 1t would be perfectly obvious to him
that the moon had some special relation to
this ebbing and flowing of the ocean. Indeed.
We are told of some savage race who. recogniz-
ing that the moon and the tides must be asso-
ciatcd were still In some considerable doubt
as to whether it was the moon which was the
cause of the tides or the tides which were the
cause of the moon.
The ebbing and flowing of the tide opens up
this chapter in remote history, which We can
now explore mainly by the help Of the re-
searches of Professor George Darwin. For as
the tides course backward and forward, sweep
ing to and fro vast volumes of water, II is OBJ
vious that the tides must be doing work. In
fact, in some places the tides have been made to
do useful work. II the water as it rises be i'm
pounded in large reservoir, 1t can be made to
turn a water wheel as 1t enters, while another
water wheel Gun be driven as the reservoir
emptios itself q few hours later. Thus we pro-
duce tidal mill It is quite true that. long as
coal remains tolerably cheap and steam power
ts consequently readily available, 1t is not often
possible to employ the direct power of the tides
IN an economical manner. For our purpose it
is merely necessary to note that, day after day,
week after week, year after year, the tides
must be necessarily doing work Of some kind.
Every practical man knows that q certain
quantity Of work can be done only by the ex-
penditure of a certain quantity of energy. He
also knows that there Is in nature no such
thing as the creation of energy. 1t is just as
impossible to create out of nothing the energy
which should lift an ounce weight through
o single inch as 1t would be to create q loaf of
bread out of nothing. II, therefore, the tides
are doing work, it follows that there must be
some source of energy on which the tides are
enabled to draw. A steam engine Is able to put
forth power because of the energy developed
from the coal which is continually supplied to
the coal in the great tidal engineer We might
et first hazard the supposition that, as the
moon is the.cause of the tides, so..we must look
to the moon 10 provide the energy by which tho
tides do their work. This, however, is not ex-
actly the case.
The match which lights the fire under a
steam boiler is in one sense no doubt the cause
Of the energy developed, but we do not there
fore assert that the power Of the engine Is de-
rived from the match 1t comes rather from
the fuel whose consumption is started by the
match. In like manner, though the moons
attraction causes the tides, yet 1t is not from
the moon that the tidal energy is drawn. There
Is only one possible source for tho energy nee
essary 70 sustain the tides. Every one who is
conversant with mechanical matters knows the
important duty which the fly wheel performs
in q mill. Tho fly wheel, In fact. may be consid-
cred as q reservoir into which the engine pours
the power generated with each stroke Of the
piston, while the machinery in the mill draws
on this accumulated store Of power In the fly