The Providence news. (Providence [R.I.]) 1891-1906, 1897-03-01
The Astronomical Future of the Earth
aud the Moon.

Perhaps the most interesting accom-
plishments of mathematical astronomy
from mundane standpoint, at any rate
are those that refer to the earth's own
satellite. That seemingly staid body was
long ago discovered to have propensity
to gain little on the earth, appearing at
eclipscs an infinitesimal moment ahead
of time. Astronomers were sorcly puzzled
by this act Of insubordination; but at last
Laplacc and Lagrange explained it as due
to an oscillatory change in the earth's
orbit, thus fully exoncrating the moon,
and seeming to demonstrate the absolute
stability and permanence of our planetary
system, which the moons misbehavior
had appeared to threaten.
This highly satisfactory conclusion was
an orthodox belief of celestial mechanics
until 1858, when Professor Adams Of
Neptunian fame, with whom complex
analyses We're n pastime, reviewed
Laplace's calculation, and discovered an
error, which, when corrected, left about
half the moons accelcration unaccountcd
for. This was a momcntous discrepancy,
which at first no one could explain. But
presently Professor Hclmholz, the great
German physicist, suggested that key
might be found i'm tidal friction, which,
acting rs perpetual brake on the carth's
rotation, and affecting not merely the
waters but the entire substance Of our
planet, must i'm the long sweep of time
have changed its rate of rotation Thus
the seeming acccleration Of the moon
might bc accounted for as actual rctarrla-
ton of the earth S rotation-a lcngthening
of the day instead of shortening of the
month.
Again the earth was shown TO bc mt
fault, but this time the moon could no
bc exoneratcd while the estimated sta
bilty Of our system, instead of being re-
established, was quite upset. For the
tidal retardation is not an oscillatory
change which will presently correct itself,
like the orbital wobblc, but perpetual
change, acting always i'm one direction.
Unless fully counteractod by some oppos-
ing reaction therefore Gas IL seems not to
bel, the effect must De cumulative, the
ultimate consequences disastrous The
exact character of these consequences was
first estimated by Professor q. III Darwin.
in 1870. He showed that tidal frictionlin
rctarling the earth must also push the
moon out from the parent planet on
spiral orbit. Plainly, then, the moon
must formerly have been nearer the earth
than at present. At some very remote
period IL must have actually touched the
I'm ..tl
thrown Off from the then plastic mass OF
the earth. ms "a polyp buds out from its
parent polyp. At that time the earth was
spinning about in day from two tn four
hours.
Now, the day has been heightened to
twenty -four hours, and the moon has been
thrust out to distance Of n quarter
million miles; but the end is not yet.
The same progress Of events must con.
tinuc, till, at some remote period in the
future, the day has come to equal the
month, lunar tidal action has ceased, and
one face Of the earth looks out always mt
the moon, with that same fixed stare even
now the moon has been brought TO assume
toward her parent orb. Should We choose
To take even greater liberties with the
future. IL may be made To appear
Though some astronomers dissent from
this prcdiction) that, as solar tidal action
still continues. the day must finally cx-
cccd the month. and lcngthcn out little
by little toward coincidence with the
year; and that the moon meantime must
pause I'm its outward flight, and come