Evening star. [volume] (Washington, D.C.) 1854-1972, 1881-07-03
IHE NATURE OF COMETS.

| W et2hed-Tbefr Orbtts-rke Nebu.
lar Hypothesis.
In the Lowell lectures OF the late Professo,
Benjamin Piece, OF Harvard College, recently
| published IA book form under the title o,
"iGeality In the PHYSICAL Sciences" Is a chap
ter treating OF the nature OF comets, from
/ Which the following extracts are made as be! ng
| CT special interest az the present time wheS
| evtry one is talking OF the new visitor which
| made such a brilliant entrance to our skies last
week:
The fin al stage of the nebulas history Is the
cor Sealed star, OF which planet satein,sa comet
and meteor are special forms and which IA O, ,s-
Ihed TO become again. at last. Oh aouc m ss-
iney are Simultaneous In existence. aud not
Ssa1ngi1g 10, 10 successive stages OF The history
passed through process OF different alton.
ara are ntted fsr different functions They
may may al De regarded as bol,d.s; and they MI
the Gel stial spaces With every c,ncelvao.e
variety OF magnitude, motion and physical as.
Iect.
The comet, from the strangeness of Its ap
pedIance In the Inaccessible firmament has
been the immemorial wonder AMI dreii o
mankind lt has been the beard or tail Of so ne
insis DE monster. Ii has been the sword OF
some angry go1. Ii has been the pen or tn,
turies. writiL 8 10 the book OF fate the death q
sfngs, the fail OF empires the speedy coming o.
,amlhes and lestilences and destru ,ttva wars.
IL mas oSen ..gst which has tllled the souls
philosophers with darkness Even the great
ARISTOTLE, with his GEAR b lief In nature AN
his contempt for superstition could propose n
Inep,y which was rot q tissue of gratuitou.
AID lhconseQuent HYPOTHESIS He thought the
comet, with lis regular motions, TO be pie
nunenon like the flGting and uncertain iJass
Jo.nes, an exhslation from the ear b.
Nevertheless even In cumstology. whers
ncdeln progress has been - essentially aid d
oy the discovery OF gravita' ion and the in
oennon OF the telescope. the instinct OF the
resuts- Passing by the researches of the
fythagoresns, we need ouly refer TO the
writings of Seneca In the first century of The
Christian era Il KNOW" writes Seneca mo
nooler research, nor a more useful science
than that which undertakes the study of the
slaIs; cut TO perfect this science is 1t not ex-
comets differs from that OF the other celestial
pooies? III We reflect on their motions on
.ueir VlclssitudeS OF rising and setting. on
tbtlr light and brilliancy, we shall be strucl,
with the analogy which we perceive between
them and these other bodies. We need an
exact history OF the comets which have
nltne,so appeared; for II Is their rarity OF
az pearance which prevents our deciding upon
The regularity Oh their movement We are 10
ncrant whether, describing liked orbits, they
90 not Iealpsar at periodic and determtnate
intervals OF Time" THIS was the predlct of
!hOught!ui genius. Modern astronomy, pron--
ng by the ancient suggestion, mas demon
stfated this, like many other truths. The
dwarf OF To- day who stands on thu sn )uIders of
the giant OF yesterday can see grea er distance
than the giant.
The perfect comet combines nucleus and
Ii unsubatantial and temporary; while the mass
ana density reside Ia the almost Invisible bur
Permanent nucleus. The solid nucleus moves
aSut the sun 10 nearly parab)ic orbit OBJ,
dient 10 the same law OF attraction which
governs the MOI ions OF any one of the planets.
whereas each particle OF the train moves In iJs
OWL % pefpolic orbit, In conssq hence OF a re-
puisich iicm the sun, often Two or three times
as great as the ordinary SOAR attraction. These
particle OF the Train are electrified DO Ies and
have the same .lecuiclty as that OF the sun:
IN nSf m 10 nrr
advance TO the front edge OF the tail while
those which are the least eeclrifi u fan backto
The rear. Some OF the particles are electrified
just enough TO balance the solar grayttarfon.
so thar, after separating from the nuc;eu rney
bic me neutral to the suns action aud m)ya
uniformly In straight lines but without ceas-
are less highly electrified remain attracted by
the sun, but move In hyperbolic orbits-iu the
opposite branch OF the hyperbola, however, to
'h All, 10 , walca th ~ repelea particles move
applied by Bessel TO the tail OF Halley's comet.
In 1885. But the comet discovered by Donatf IN
lsss oIeied as me an opportunity as can be
the Beauty OF that comet! All the world stopped
In the street, when II became visible after tWI-
light, and wondered at it with batei breath A
velsal d1Smay. and men would have pilei az
the frigbtful porCent. But the Christian OF to-
day beholds it as the love lest messen ger of
Divine wisdom. A multitude of obsery Itions
were made upon the train as we'll as tns head
In al CivlilZed cOuni rieS and the theory or the
t'a'n was sustained In every detail The ele-
gaLGe OF inc shape strictly c,nformed to the
iceal construction OF the geometer.
IL the nucleus OF comet were taken away
Tie train would continue to move of through
space. uiidisturbed by the loss OF its head SIN
guar a. this phenomenon may seem 1t has be IN
actually observed. At midday on the 2S n OF
February. lSi3, groups OF people In many OF the
towns OF New England, especially at PJrtla I'd.
collected at the corners OF the streets gazIag
up toward the sun. Protecting their eyes Ia
the shaCeN OF the houses they saw brtlu3n
ohJsct feW degrees from the sun. Such amar
Vicious spe ctecle had never before been beheli
few days later wonderfully brilliant TAN OF
comet was 81 en- skfrtiDg the horizon soon af-
ter sunset and reaching m IRE than one third of
the way round the sky. What We now saw vas
tall without head. as we had before seen head
most destitute OF tail But head and tall were
members OF the same comet.
In ABOUT TWO hours the comet OF 1913 went
round the sun, from one side to the other. What
could have become OF the TAIL which was reach
ing out about hundred millions o. miles from
the sun as far as to the earth's orbit? There
have been those who have actu ally adopted the
tic: edibie-l may say the mposslble-hypothe
Sis that tie tail rotated through this immense
circuit, Developing centrifugal force which all
the united powers OF the universe couli not
have sustained. But no! The comet practi-
cally left its taii behind iG and began to grow
rev tall as 1t receded from the sun. There
were thus Two tails, nearly side by s1de stretch
Ing from opposite sides OF the sun In ne arly the
sane direction. The new tail began at the
head OF The comet; whereas the cid deserted
tail began without any head at some distance
from the nucleus and eXtenied further from
the sun than the new tall
The bucleuS or the comet Is surrounded by
mist, Which Is called the coma, or hair; the
name comet signify1ng a hairy star. Tae
height OF the coma above the nucleus d epends
on the mass OF the nucleus, and gives The
measure OF It's weight; or, more exactly the
least Limit OF weight which will sufr1ce to mala.
tain such height OF atmosphere. The nucleus
is usually SO closely surrounded by the dense
mist that its diameter cannot be measured: but at
times the mist rises, uncovers the nucleus and
leaves IL with sharp stellar aspect. Tue lie ,St
diameter determined az such times may laryer
than the actual enc, but cannot bs smaller
Front he combination OF mass and diametpr'th
density Il The nucleus can be computed 10 the
case OF Donati's comet, the diameter OF the
nucleus was perhaps not more than hundred
mites while the height OF the atm oSphsre eX-
tended to eighteen thousand miles, You may
be surprised TO learn that the corresponding
density OF The nucleus was at least equal TO
that OF iron. What an unexpected contrast is
here prtfented to the prevalent notions con-
G. rntLg the sun and the comets The soid sun
the substance of the ETHEREAL comet Is sohd
and heavy metal
In It's approach to the sun the surface OF the
nucleus Is rapidly heated; 1t Is melted and vap.
oiizet and subjected to frequent explosions;
the VapOr rises In its atmosphere with q well
defined upper surface, which is known to OBJ
servers as an envelope. Various envelopes In.
GLIDING each other, are often observed.
The identification OF the cOmeCary mist Is
analogous to that OF our own thuncer-cloud.
Any portion Of the coma which has received