National Republican., 1873-12-11
MODERN ASTRONOMY.
PROF. NEwcouB.s FIFTH Lp,ru


The nah lecture on astronomy was delivered by
Professor Ncwcomb before the Columbian INT
Norsity. The Professor began by stating that the
present lecture Of his course would he devoted TO
an account OF the results Of the theory OF Erayita
tion as they had been worked out by the great
mhthomnticlans since Newton. The achievements
Of these men may justly he regarded az the great.
est OF the human intellect. Among problems nd.
mitting Of solution none could he presented more
completely hopeless than that Of determining, by
purely mathematical rcnsonlng. the motions Of
such system Of bodies NJ that Of the SUN and
planets arising from the attractions of each
pnc hyall the others. In fact, the problem was
beyond the powcr Of any buc mind, It's solution
having taxed the powers Of .ucccssiyc generations
Of mathcmntIcians ffum Newton forward, and
beIng s;ill In an incomplete stats.
MENTIONS "rR.NCIriA."
=. The lecturer then prosecuted To explain how
Newton gitaekcd The problem In his Principal"
" was well known that the moon did not move in
exact accordance with kcplcr's laws, and Newton
lTgan by showing that the deyiutiUns were due 10
The attractions oi the sun on the moon. II the
move exactly In an in,arnble cllipsc. But the at
traction OF the sun on the moon Il really much
grenter than that Of the earth on the same body,
sothat u might at hrst sight appear ns II tie
moon ought TO be wholly pulled away FROM The
earth, But the sun attracts the earth also nn, il
the attraction on the earth and moon were the
sa,nc they would continue to move around each
other lust as IL the attraction did not exist The
quantity or direction, and The difference OF the
two acts as disturbing force, tending to change
the relative positions Of the two h"dlcs a dia-
gram was crhlbited, showing how these forces
ac,ed, and In what way they tended to make the
moon move.
FierRK OF THE EARTH.
The next subject to which Newton applied his
was held in place by the earths attraction, and il
the latter were at rest, It's surface would be
spherical. Set the earth revolving on It's axis
TO bulge out, while the poles will be nattcncd
Moreover, bodies will be lighter at the equator
SS'n oeesnse , Of The centrifugal iorcc generated
from the cnrlh's centre. Therefore white the
Theory OF grar'ation was stll In doubt, It became
very important to know, by actual measurement
whether the gure Of the earth was really what
Newton sad must be. Tho requisite mca sure-
mcnts were n,,dcrtnken by the French Goycrn.
m.ni, under the auspices Of the Academy Of
Sciences, hut the result seemed to show that
within the limits Of France the earth showed no
such deviation from the spherical form as Newton
announced, hut rather seemed 10 be elongated in
the direction OF the poles. This result arose en-.
urciy from the impcriections Of the instruments
used to uetcrminc the latitudcs OF the several sta
iiahs The advocates of Hrayitstion would not
vivc up the question on such Insufficient data and
one to Lapland aud the othcr 10 Peru, Inc meas
ures made by these expeditions proved concIu.
si'ely that the degrce OF latitude was longer
In Lapland than In France, and therefore that ihe
result Ot the theory of graytgtion was correcI
II Is now known that the equatorial diameter OF
the earth is about twcnty y.seven miles longer thnn
the polar diameter. hut the exact lcnai6 Il stni
somewhat IN doubt, owing to the difficulties In Inc
way OF an exact determination. Indeed, there is
reason To believe that the equator itself Is not a
perfect circle hut has many irregularities and
perhaps, n slight elilptIcity.
Anintsrr,t,ng consequence Of the nattening Of
the earth at tue poles Is that II pendulum clock
which keeps time at Washington will lose nearly
two mnutesa day at the equator owing TO the |
,a,mlniton Of the effect Of gravity on the pendu.
fRlcEssloSs OF TuE rauISaSEs.
The motion Of the earth's axe which .iyes rise |
to the procession OF the cquinoNes. was tR-n sx:
planned to he due to the attraction uf the sun sud
inooa on the excess Of matter ~ the earth equa-
tor. II the earth were perfectly round, llspYis !,
would always point absolutely III the saline direc.
Ion IN space, and the same star would always b,
form OF the earth, the attractions OF the s,,n and
moon eausc It's pole to describe circle Of about
time Of each revolution being nearly twenty.6ye
thousand years.
c.ocys OF kr.nx,rY.
The variations of the planetary orbits In the |
cour,e OF ages were next explained. The cnrth's |
time Of Hipparchus, but Is more nearly circle. |
The orbits Of other planets have been growing |
continue to do so for thousands OF years 10 come
II this change Is to continue the planets Will |
tnally deyate so widely from their present |
ncarly circular orbits US 10 be thrown luost into
the sun at one time, and carried far away like |
comets at another time, the present order Of the
ture Of the human race to know what the futurr
form OF the earth's orbit Ia to be- 10 trace effect.
50 complicated and remote was entirely beyond |
the power OF mathematical analysis In the time Of
Newton. but the great French mathe enAtc cians.
la Place and Lagrange, were able to show that |
the changes ln question would not 90 Ql forever,
but that all the planetary orbits would lofeycr |
oseulate between narrow limits, and they even
set bounds outside Of which no planet eoui ever
pass. But the times Of these oscillations are most
enormous, ranging up to half a million Of years.
The earths orbit has been widening out for |
2D,0D years past, and will csntinue TO do SO for |
S,Wp years to come. II will then begin TO con. |
tract, aud will continue to do for $1,000 years
The cecentrlcity Of Mercury has been steadily
Increasing for the last hundred Thousand years
but has now nearly attained Its limit. In about
hye Thousand years II will begin to dinlnish and
Will continue to do so Tor more than q hundred
thousand years The orbits Of the planets must
go on oscillating IN this manner as long as the |
laws Of nature remain unchanged, forming what
a French writer has called great clocks al cter-
nty. which beat ages US Osrs heat seconds"
The lecture Terminated with short account of |
thc labors of the mathema,ieans to perfect the
Know ledge oi the moons motions. Although our |
lunar TABLES were now much more accurate than |
iorneriyI the! did not entirely correspond to the
SiaSSity WI stitf oTsSSfs. '"u '"s cause 0' the