New-York daily tribune. [volume] (New-York [N.Y.]) 1842-1866, 1850-11-19
THE HEAVENS-THE MOON:
A LECTURE.
Lsketched for The Tribune
By PRor. o. NJ. Mitchell, OF CIScINSA7


Among the number of orbs which fill the Heay.
ems. said Prof NJ there is no one which has ex-
cited so much interest or so absorbed the atten.
ton of it's behoders the Moon. From the ear
Hest ages, in which we have any accounts OF the
observation Of the celestial phenomena it has
gagged the attention of the Astronomer, and prob
ably the first observation OF the movements Of the
Heavenly bodies made by man was caused by
her changes. When history begins to shed light
upon the world it shows the greatestminds en-
gagged in the investigation oil her phenomena,
and from the days of Ptolemy down to the pres
ent day the interest excited by the Moons
movements has not abated.
w 18th three bodies are we specially and more
Immediately concerned; the Sun, the Earth and
the Moon, When the Astronomer first directed
his attention to the starry vault, he saw that the
Sun maintained its position that each day it pre-
sented the same appearance but the Moon was
constantly changing. One night he saw It III the
direction OF particular cluster OF stars, but the
next night it had gone up in direction contrary
TO the general movement OF the Heavens.
But not only did it change its position but also
its form From the SLENDER silver crescent rising
but little behind the Sun,lt gradually becomes iuii-
olbed and appears as the Sun goes down; then
by the same degrees loses its size till 1t is gone
We, to whom the causes of the phenomena are
familiar cannot appreciate the difficulties which
they must have caused III the minds OF the nrst
Observers. The Sun shone with a uniform hight,
while the Moon appeared and disappeared, chang
ing her form and br1lliancy. Were they not both
self-umnous Then why the variance This 1t
was not practicable to explain till more striking
phenomena had been observed and accounted
for. The solar and lunar ecHpses, so terrific to the
untaught ancients We're the key to unlock the
mystery.
Let US said Prof NJ. follow the train by which
the causes of the cclipses were arrived at, and
see how they explained the phases of the Moon,
1t was all performed without the aid OF inst'u-
ments by simple observation of the Stars, and by
the same method any one can,Wlthout the ali OF
book perform that great feat of early science, pre-
dict an eclipse.
Tie Moon by observing her position in regard
to the fixed Stars, was found to change her place
from day to day, that in about month she
made complete circuit OF the Heaven. BY the
stars, as waymarks, her track was laid down.
and by watching revolution after revolution, her
periodic time was computed.
1t was next observed that while the liked Stars
moved round the Earth, apparently, IN parelled
courses the Moons track was obhque to them.
By continued observation! 1t was found that
the Moons path was oblique from that of the
Sum- and that il both were to leave luminous
track behind them the two rings would cross IN
two points.
The Astronomer notices that whenever a solar
eclipse takes place, the Moon is absent that Just
before the eclipse takes place, it is but little
before the Sun and exhibiting its narrow and
fast diminishing crescent; after the eclipse he
sees it again Just behind the Sun as the new
Moon. He computes the time between the two
appearances and the conclusion is inevitable that
the Moon must have been between him and the
Sun at the moment the eclipse took place Now
how shall he be able to compute the time before
the circumstance shall again occurl He has no.
tced that the track of the Moon and Sun touch
each other III only two points, called the nodes.
And the Moon can only be between him and the
Sun at that point in her orbit. Neither can an
eclipse occur except at the new Moon, when the
Sun and Moon rise together Knowing the time
from new Moon to new Moon and from node to
node could he not combine them together He
watches each revolution, and finds the new Moon
comes nearer and nearer till they coincide and the
time counted. The lunar eclipse he explains
IN the same manner, finding that it occurs only at
the iull Moon when the Sun and Moon are on Cd.
poste sides OF the Earth and that that too only
happens at the node. The truth is thus inevita.
bly, thrust upon the observer that the Moons
light is borrowed from the Sun, and knowing this
the explanation OF the phases is easy.
These simple observations We're to be made
with the eye alone, but when Instrumental aid
was brought in, various Irregularities were exhib.
tied The nodes were found to change their posi-
ton making complete circuit in nineteen wears;
the orbit oil the Moon was found to be Irregular
IN form, her speed not to be uniform and other
disturbances were shown which have required
the most profound analy sis to explain
When the Earth was dethroned by Copernicns
the only faithful attendant was the moon, and the
system which made her an exception gave the
reasons ior her pecullarites. keplers three laws
explained many OF her phenomena These laws
are that the orbits of all the planets are eliptica
that the area passed over by line drawn from
planet to the sun is equal in equal times and
that consequently they move more RAPIDLY when
/ III the nj 1 IL:
thal the periodic times OF planets varied according
70 'her distance from the SUM- the squares Of their
times increasing as the cubes OF their distances
increase 1t was found that the Moons orbit
vas but slightly ehptical, since her apparent dia
meter was not much varied What keens her
there THIS question was answered bv Newton
by means OF a law which the Moon revealed to
him. He conceived the idea that bodies exerted
an attractive influence upon each other in aD in.
verse ratio with the square OF the distance which
separated them NO elevation whichhe could at.
tam was sufficient to test the theory
tie appealed 10 the Moon and received nm nm.
sWer from our distant neehbor. He made n cal
Culatlon CT the force which the earth ol1Sht IN
exert upon the Moouat her distance accordjn., 10
ms theory and proceeded TO drop tile Noon to the
Earth To see whether the truth corresponded win
1t, In other words he calculated the momentum,
OF sueh body moving with its speed-and fonod
thai Tue power required to turn 1t out of straight
aue 10 circle was equal to the computed attrac.
t.an.
Having discovered this law, he applied it to the
operations OF the Planets. Were the sooner put in
motion and no disturbing influence exerted, the
orbit would remain unchanged. but syor,s nloY,et
IS drawing ii toward Itself, and the orbit is con.
stantly moved about, and is figure is constantly
changing The revolution OF the line of nodes
was accounted Tor by the attraction OF the Sun
mon mon tie Moon Some ii the changes IN the
MoeA orbit Newton considered ;uexplicable BY
his newly discovered law. but after long contr6.
ve1sy they We're rendered clear.
By a comparison Of the accounts Of ecpses by