Evening star. [volume] (Washington, D.C.) 1854-1972, 1881-07-02

teOrS-The Electrified Train-T0il.
less Cemets-HOvy They Are
Weighed-Their Orbits-The Nebu-
lar Hypothesis.
In the Lowell lectures Of the late Professor
Benjami Pierce, of Harvard College, recently
published In book form under the title OF
"ideality in the Physical Sciences" Is a chap
ter treating OF the nature Of comets from
which the following extracts are made as being
Oh special interest at the present time, when
every ore is talking Of the new visitor which
made such bl f'liaht entrance TO our skies last
week:
The fio al stage OF the nebular history Ia tho
CONCEALED star, OF which planet, satellite, comet
ana met cor are special forms, and which is de5-
tnt0 10 become again, az last, Oh A0tlc IN 49,.
They are simultaneous In existence, and not
belonging TO successive stages OF the history.
StartiLg from common origin. they have
passed through process Of differentiation
aid are fitted for different functions They
may all be regarded rs bold. 8; and they I'LL
the col stial spaces with every c)nce.vao
variety OF magnitude, motion and physical as.
Iect.
The comet, from the strangenes, of Its ap-
pearance In the Inaccessible firma h IS
been the immemoriai wonder AMI dreai O
manKlnd. lie has oeen the beard or tail OF soma
inslsl PIE monster. It has been the sgord OF
turfes. writing 10 the book OF fate the death
kings, the fall OF empires the speedy coming of
,am1nes and pestileaces and destru Give wars.
tt has been light which has filed tn, s,u.Io
philosophers With darkness. Even che greli
Aristotle, With his clear b slief Ia nature an
his contempt for superstition, could propose n
theory which was not tissue of .gratuttou
and incOrsequent hypothesis. He til )uynt the
comet, with lts regular motions, to De phe
nomenon like the fitting and uncertain tynti
Nevertheless. even in comstology. wnere
modern progress has been Sd essentially aided
by the discovery OF gravita'ion and the in
vention OF the telescope. the instinct OF the
ancient thinkers achieved some memorable
resuts- Passing by the researches Of the
Pythagoreans, we need only refer 20 the
Christian era. Il KNOW" writes Seneca. mi
noDler research nor more useful science
tran that which undertakes the study OF the
stars; but to perfect this science is it not ex:
comets differs from that OF the other celestial
bodies? II We reflect on their notions on
their vicissitudes OF rising and setting. on
their light and brillIancy, we shall be struck
With the analogy which we perceive between
them and these other bodies. We need an
exact history OF the comets which have
appearance which prevents our deciding uoon
the regularity Of their movement We are IL.
norant whether, describing fixed orbits, they
90 not reappear at periodic and discriminate
thoughtful genius. Modern astronomy, profii-
iIg by the ancient suggestion, has demon
stIated this, like many other truths. The
dwarf OF to- day who stands On the sh builders OF
the giant OF yesterday can see grea1 er distance
than the giant.
The perfec. comet combines nucleus and
tIaiD: The beauty belongs to the train, which
Is uIsubstantial and temporary; while the mass
and density reside IN the almost invisible bu5
permanent nucleus. The solid nucleus moves
about the sun In nearly parab0ic orbit, obs
governs the mo- ions of any one OF the planet:
whereas each particle of the train moves In IFS
own hyperbollc orbit, In consequence OF a re-
puislon from the sun, often two or three times
rV or tfr, IN,
particles OF the train are electrified bodies, AID
have the same electricity as that OF the sun:
the particles which are most highly electrif19 ii
advaLce to the front edge of the tall, while
those which are the least electrified fan back to
the rear. Some OF the particles are electrified
just enough to balance the solar gravitatlon;
become neutral 10 the suns action aud move
uniformly In straight lines, but without ceas-
II 10 De part of the tail. The particles which
are less highly electrified remain attracted by
the sun, but move in hy periodic 0rbitS-in the
opposite branch OF the hyperbola, however, 10
that In which the repeiled particles move.
This theory. In an imperfect state, was rud ely
applied by Bessel TO the fail OF Halley's comet,
tn 1885. But the comet discovered by Donatt In
1888 Oneled as fine an opportunity as can b3
desired for Its full veriflcation. How grand was
=, sae neau.y OF tnaI comet! Az the world stopped
IN the street, when It became visible after LWi-
light, and wondered at iJ with bated breath A
Few centuries ago 1t would have caused uni
versal dismay, and men would have paled a,
the fr1gntful portent. Bu5 the Christian OF To-
day beholds 1t as the lOveiest messenger of
Divine wisdom. A multitude Of ob5erv Alton
were made upon the train as we'll as the head
In all civilized countries and the theory of the
train was sustained In every detail The ELL
gance OF the shape strictly conformed to the
ideal construction OF the geOmeter.
II me nucleus OF a comet were taken away
the train would continue to move of through
space. undisturbed by the loss of its head. Sin.
guar as tnls phenomenon may seem IL has been
actually observed. At midday OF the 2S.h Of
- nj nlo ty&yv
towns Of New England, especially &C Portland
collected at the corners Of the streets gaZIUg
up toward the sun. Protecting their eyes In
the ShaCoV 5 OF the houses they saw brilliant
OBJECT few degrees from the sun. Such mar
Vicious spectacle had never before been behe,d
A lew days later wonderfully brilliant tail OF
a comet :" as seen skirting the horizon soon at
Ter sunset and reaching more than one third OF
The Way round the sky. What we now saw was
tall without head. as we had before seen he I'd
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 OF miles from
the sun as far as TO the earth's orbit? There
have been those Who have actually adopted tins
IL CT edible-l may say the mpossible-hypothe-
Sis that the 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 pract1-
cally left its tau behind IL and began to grow
were thus two tails, nearly side by side, stretch
Ing from opposite sides of the sun In ne rly the
same direction. The new tail began at the
be ad OF the comet; whereas the old deserted
all began without any head at some distance
from the nucleus and extended further from
the sun than the new tail.
The LucleuS or the comet Is surrounded by a
mist. which Is called the coma, OF hair; the
name comet Signifying q hairy star. Toe
height OF the coma above the nucleus depends
on the mass OF the nucleus, and gives tina
measure Of its weight; or, more ex actly. the
least Init OF weight which will suffice to m Ia
tain such height Of atmosphere Tue nucleus
Is usually so closely surrounded by the dense
mist that Its diameter cannot be measured; but at
UneS the mist rises, uncOverS the nucleus and
leaves IL with sharp stellar aspect. The least
diameter determined at such times may be larger
tban the actual one, but cannot be smale".
From The combination OF mass and diameter, the
density CT the nucleus can be computed. In the
case OF Donatfs comet, the diameter Of the
nucleus was perhaps not more than hundred
miles. While the height OF the atmosphere ex-
terde d to eighteen thousand miles. You may
be surprised to learn that the corresponding
that OF iron. What an unexpected contrast is
here presented to the prevalent notions con-
ctrning the sun and the comets! The solid sun
Is reduced by science to the state of gas. while
the substance Of the ETHEREAL comet is solid
and heavy metal
In its approach to the sun the surface OF the
nucleus Is rapidly heated; 1t Is melted and vap.
oIlzed and subjected to frequent explosions;
lne vapOr rises In It's atmosphere with we'll
defined upper surface, which Is known to OBJ
servers as an envelope. Various enyalnpea in