The sun., 1895-05-26

It's stores the consequence II Inevitable. TIL
quantity of energy due TO the rotation of tn
earth must be gradually declining. statc'
In this way perhaps the intlmation Is not yer,
alarming, but placed In other words the result
at which we have arrived assume tho NOR
practical expression that the tides must III
gradually checking the speed with which til,
earth turns round. The tides must, In fact
be increasing the length Of tho day. In con
| sequence Of tho tides which ripple 10 and fro OF
our shores, and which flow In and fow out o
our estuaries and rivers, to-day is longer thar
yesterday and yesterday Is longer than the day
| before. may, however, admit at once that the
| change thus produced In not very appreciable
| when only moderate periods of time are con.
sidered. Indeed, the alteration in the length
| of the day from this cause amounts to no more
| than n fraction of a second In period of q
| thousand years. Even in the lapse of ordi-
| nary history there is no recognizable change in
| tho length of the day. But the importance of
| our argument is hardly affected by tho circum-
stance that the rate at which the day Is length
eniDg is very slow one. The really significant
point Is that this change Is always taking place,
and lies always In the same direction.
1t is this latter circumstance which gives
to the present doctrine its great Importance as
a factor in the development of the earth-moon
system We are accustomed in astronomy to
reason about movements which advance for
vast periods in one direction, and then become
reversed. Such movements rs this. however,
are not the real architects of the universe,
for that which Is done during one cycle Of
years is undone during the next. But the tides
are ever In operation and their influence tends
ever in the same direction. Consequently the
alteration in the length of the day is continu-
ally in progress, and In tho course Of illmita-
BILE ages its effects accumulate to startling
magnitude.
The earth now revolves on its axis once in
twenty-four hours. There was time, millions
Of years ago, very likely, when 1t revolved once
in twenty-three hours Earlier still 1t must
have spun on its axis In twenty-five hours,
while this succeeded a time when the day was
only twenty hours The very same arguments
applied in those times, which apply at the
present. 80 that II we strain our vision back into
the excessively remote past, we find the earth
spinning ever more and more rapidly, until at
last we discern an epoch when the length of the
day was something like five or six hours. This Is
the time when the moon s.story commences. At
this eventful period the earth accomplished
about four revolutions in the same time that
1t now requires for Il single one. We do not
attempt to assign the antiquity of this critical
moment 1t must certainly have been far ear
lier than the time when this earth became
fitted for the reception of organized life. It
must have been at least ma ny millions of years
ago. If 1t be thought that the vagueness of our
chronology is rather unsatisfactory. then it
must be remembered that even historians who
have human records and monuments to guide
them, are still often in utter uncertainty as to
the periods during which mighty empires
fourished, or as to tho dates at which great
dynasties rose or perished.
But our story has another side to 1t. Among
the profoundest laws of nature Is that which
asserts that action and reaction are equal and
opposite. We have-seen that the moon is the
cause of the tides, and we have further seen
that tides act rs a brake to check the speed
with which the earth Is rotating. This is the
action of tho moon upon the earth. and now
let us consider the reaction with which this
action must be inevitably accompanied. In our
ordinary experience We observe that man
who is annoyed by another feels an unregener-
ate impulse to push the annoying agent away
as far as possible This is exactly the form
which the reaction Of the earth assumes 1t is
annoyed by the moon. and accordingly 1t
strives to push the moon away. Just as the
moon by it's action on the earth through the
medium Of the tides, tends to check the speed
with which the earth Is rotating on its axis, SO
the earth reacts on the moon, and compels the
satellite to adopt O continuous retreat. The
moon Is, therefore, gradually rcceding. 1t Is
terday; 1t will be further tomorrow than 1t is
to-day. Tho process Is never reversed; it
never even ceases. The consequence Is q con-
tinuous growth In tho size of the track which
the moon describes around tho earth. It is
quite true that this growth Is slow one; SO,
too, the growth of the oak is imperceptible
from day to day, though in the lapse of CEN
turies the tree attains a magnificent stature.
The enlargement of the moons orbit, though
imperceptible from month to month, or even
from century to century. has revolutionized
our system in the lapse Of millions of years.
Looking back through the mists Of time, we
see tho moon ever drawing nearer and nearer
to the earth. Our satellite now revolves at a
distance Of 100000 miles, but there was a
time when that distance no more than
100000 miles. There was time, millions of
years ago, no doubt, when the moon was but
100, 900 miles away, and we look further
and further back see the moon ever
drawing closer and closer to the earth, until at
last we discern the critical period in earth-moon
history, when our globe was spinning round in
q period of about five or six hours The moons
instead of revolving whore we now find 1t, was
then actually close to the earth, earlier still it
was in fact touching our globe, and the moon
and the earth were revolving each around
the other, like q football and q tennis ball ac-
tually fastened together.
1t Is impossible to resist taking one step fur
ther. We know that the earth was at that
early period soft molten mass of matter,
spinning round rapidly. The speed seems to
have been 80 great that O rupture took place, a
portion of the molten matter broke away
from the parent globe, and the fragments coal
esced into a small globe. That the moon was
thus born of our earth uncounted millions of
years ago. Is the lesson which mathematics de-
clares II learns from the murmur of the tides
ALL HANDS DANCED,
.U,,., nuu.o. ntd 49,.