New-York tribune., 1872-05-08
THE NEBULAR HYPOTHESIS
A LECTURE BY PROF. JOHN FISKE OF HAIR
WARD UNIVERSITY.

SOLAR sYsrEM-THE MOON A " DEAD PLANET
-HRAT AS AN ASTRONOMICAL AGENT-Ihh
EARTH DOOMED TO FALL INTO THE SUM-
Prof. John Fiske delivered his lecture on
,.rhe Nebular Hypothesis" yesterday afternoon anu
again in the evening intelligent audiences Nv ~
rooms of the American Geographical ooeioV, 100 ,ano
Institute. The lecturer began by menuohns 1870 u -
tary revolutions which have become so iamii'. " Is
that VIC commonly overlook them atoee'no' ,ne
sheer tnateutiyeness failing to realize their
though their harmonious relations us i'"p".o "
shovn prove that the various meinoers Vi 'i' s 0
tam have had common origin. Inc ciue W "'''e e
mon origin may be sought IN 'ac.s wh'0n "iV o"'iy
occurring before our very eyes Every nlemDer OF
- planetary system is constantly parting with
molecular motion the shape OF heat Our earthl III
tlv pouring out heat into surrounding space
and although the loss temporarily made good py sonar
radiation not permanently made good as Is proved
nv the fact that during many millions Of years the earth
has been slowly cooling. The evidence is overwhelming
which that the earhs surface was once hotter
than the fame of an oxy hydrogen bow-ppe Inc moon
also is cooler than formerly is shown by the TACT that
the supeudous forces which once upheaved ts great
volcanoes now quescent The sum- too' Is pouring
away heat at such rate tha-accordng to Hersehei-
ma cylinder Of miles in length and As miles IN
diameter were darted into the sun every second IL
would be melted as fast as it came.
PLANETARY GENESIS
There Is every reason for believing that sun, moon, aud
earth as the other members OF our system, nave
been from mmemorial losing moro heat than they
have received in exchange As in losing heat all bodies
contract ii that the various members of the solar
system must all be much smaller than they were at the
outset Though they increased IN mass by appro
prating large quantities of meteoro dust they must at
the same time have greatly decreased IN volume %
yiousy therefore, il to go back far enough we
shoud find the earth filing the moons orbit 80 tnat
the matter composing the moon wouio
then have formed part OF the equatorla
region Of the earth. At period still more
remote the earth itself must have formed tiny portion
Of the equatorial region OF the SUM- when then ned Cuc
earth's orbit ti earlier date tue solar system
ust have consisted simply of the which, than
nling Nepune's orbit and consisting OF widely -dfused
vapors merited the name Of nebula rather than OF
star In slow concentration OF this solar nebua the
present pecuarites Of the solar system may find their
explanation The loss of heat radiaed into the
surrounding space caused steady contraction OF the
collar mass; WHILE the other hand, the increasing
rapidtY Of its rotation impressed upon those parts
of IL nearest the surface a tendency TO NY
off into space, least to remain behind instead
of accompanying the central portion of the body IN its
contraction. AS in every rotating spheroid, this cen
trfugal force greatest where velocity is greatest
at the equator-a time came the history OF vapor
when the bulging equatorial portion no longer
able to keep pace with the rest In ITS contraction was
left behind a detached ring surrounding the central
which ring soon broke up into many fragments OF
uneoual dimensions. At this stage, then, we have
host of satellites surround the solar EQUATOR revolv
ing in the direction of the solar rotation following each
other in the orbit and gradually becom
ing ngglomerated, by gravitative force into a sphe
roidal body, having o velocity compounded OF the
several veocites of the fragments and rotation made
up OF their several rotations. Meanwhile the central
the sun, cooling and contracting, left behind
second equatorial be which, breaking and consolidating
after the became the planet Uranus. Ia
like manner were formed all the planets and their
satellites Such is the grand theory OF nebular genesis
in Which, as Mill reminds us, is unknown substance
introduced suppositon unknown property OF
law ascribed q known substance" 1t involves none
but established mechanical and dynamical principles.
SIZE OF THE PLANETS.
According 10 the nebular theory, the outer planets
ought in general to be much larger than the inner plan
ets because the ancestral rings which concided with
the immense orbits of Uranus and Neptune must Of
course been larger than the stra rings which
conceded the smaller orbits Of Mars and the Earth
But this is a complete explanation; for the case
stands there ought to be regular gradaton in the
sizes planets The four outer planets indeed
much larger the four inner But OF the inner
group the largest Mars but the Earth while n the
outer group find Jupiter 81 times large Saturn,
which in turn is times larger than Uranus. The
cause OF these apparent anomalies is 10 be sought the
shapes OF the rings from which the respective planets
we're formed, Neptune and Uranos were formed from
thin hoopke rings, period when the solar equator
protruded but little AS the solar spherod continued 20
contract increasing equatorial velocity rendered
more and obAte in figure, % TIA, The rags next
detached quoltsbaped- Hence the resulting planet
not only had their major bat lille lc4ae
their orbit planes. but they we're also aFrpr
After the formation OF Jupiter, - attraction With that
Of other planets already formed exsrted upon tie
solar equatorial zone. entailed a different
series vhich, n the absence
OF external force, must have been thick quoits be-
cause Of the stI Increasing oblSsness Of the solar
spheroid detached prema tUrely by JupIters at
traction that they again sppro1iated to the hoop
shape The extreme smaIlness OF the planets is
thus due 70 the smalness Of their orbits cOnbBed with
the slightly hooped shapes Of their ancestral rngs that
Of Mars having been the most slender OF the four.
Curiousy enough, il examine the different systens
of satellites We mud the general contrast in size
between the members OF outer and inner groups.
PLANETARY DISTANCES
Further evidence In behalf OF this theory OF nebuar
genesis is furnished Bodies law Of planetary distances
Though the case OF Neptune affords apparent excep
ton, the remaining planets exhibit remarkable serial
uniformity distances from the center Of the
fem ANY given planet is nearly twice far from
sun as the next planet. Another confirmation OF
The hypothess found in the distribution OF satel
htes. Since the detachment OF a mo0nfOrmlng ring
from contracting planet depends the excess of cen
frfuga force at the equator, il s evident that rings will
he most frequently detached those planets which
the centrifugal bears the highest ratio TO gravi-
tation Such planets will have the greatest number OF
moons And SUCH fact is the OF the four inner
planets which slowly, and in which the centrfu-
gal force Is small, only the Earth (and perhaps
yenus) is known 10 have satellite; but Jupiter
whose centrifugal force is twenty times greater
than that Of the inner planets, has four
satellites; Uranus with still greater centrifugal force
has four, and probably six eight moons; and
finally Saturn in which the centrifugal force is one
sixth Of gravity being nearly fifty times greater than
Earth has eight besides his three unbroken
han Naattt. f1a fpaYna ifv nff