West-Jersey pioneer., 1881-07-07

of comets can be determined, the periods o
their revolutions calculated, and the time
of their appearing predicted. Other grea
comets were seen in 1744, 1853, 1871 ant
1S43. The last named was probably iden
tcal with that of 1889; it was visible IL
broad daylight, without the aid of glasses
and approached to within 600, 900 miles o
the sun, being the ''closest shave" on record
Donati's comet appeared in 1858, and was
remarkably brilliant. It's period of revolu'
tion is 1850 years, so those who missed see
ing it then will probably not have another
opportunity. Other large comets were seen
in 1861 and 1874.
| The perfect comet combines nucleus and
train. The beauty belongs to the train.
which is unsubstantial and temporary, while
the mass and density reside in the almost in
visible but permanent nucleus. The solid
nucleus moves about the sun nearly para
bolic orbit, obedient to the same law of at
traction which governs the motions of any
one of the planets; whereas each particle of
| the train moves in it's own hyperbolic orbit,
in consequence of repulsion from the sun,
often two or three times as great as the Or
dinary solar attraction. These particles of
the train are electrified bodies, and have the
same electricity as that of the sun; the par
ticles which are most highly electrified ad-
vance to the front edge of the tail, while
those which are the least electrified fall back
to the rear. Some of the particles are elec-
trified just enough TO balance the solar grav-
itation; so that, after separating from the
nucleus they become neutral to the suns ac-
ton and move uniformly in straight lines,
but without ceasing to be part of the TAIL
The particles which are less highly electri-
fed remain attracted by the sun, but move
in hyperbolic orbits-in the opposite branch
of the hyperbola, however, to that in which
the repeled particles move.
This theory, in an imperfect state, was
rudely applied by Bessel to the tail of Hal
ley's comet, in 1885. But the comet dis
covered by Donati in 1858 offered as tine an
opportunity as can be desired for it's full
verification. How grand was the beauty of
that comet. All the world stopped in the
street, when it became visible after twi-
light, and wondered at it with bated breath.
A few centuries ago it would have caused
universal dismay, and men would have
paled at the frightful portent. But the
Christian of to. day beholds it as the love-
liest messenger of Divine wisdom. A null
titude of observations 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 elegance of
the shape strictly conformed to the ideal
construction of the geometer
If the nucleus of a comet were taken away
the train would continue to move off through
space, undisturbed by the loss of its head.
Singular as this phenomenon may seem, it
has been actually observed, At midday on
the 2Sth of February, 184S, groups of peo-
pie in many of the towns of New England,
especially at Portland, collected at the cor
ners of the streets, gazing up toward the
sun. Protecting their eyes in the shadows
of the houses they saw brilliant object a
few degrees from the sun. Such marvel
GUS spectacle had never before been beheld.
A few days later wonderfully brilliant tail
of comet was seen skirting the horizon
soon after sunset, and reaching more than
one-third of the way round the sky. What
we now saw was the tail without head, as
we had before seen head almost destitute of
tail. But head and tail were members OF
the same comet.
In about two hours the comet of 1S43
went round the sun, from one side to the
other. What could have become of the tail,
which was reaching out about a hundred
million of miles from the sun as far as to
the earth's orbit? There have been those
who have actually adopted the Incredible
l may say the Observation-Disclosures that
the tail rotated through this immense cir
cult, developing centrifugal force which
all the united powers of the universe could
not have sustained. But no! The comet
practically left it's tail behind it and began to
grow new tail as it receded from the sun,
There were thus two tails, nearly side by
side, stretching from opposite sides of the
sun in nearly tie same direction. The new
tail began at the head of the comet; where
as the old deserted tail began without any
head at some distance from the nucleus, and
extended further from the sun than the
new tail.
The nucleus of the comet is surrounded
by a mist, which is called the coma, or hair;
the name comet signifying hairy star.
The height of the coma above the nucleus,
depends on the mass of the nucleus, and
gives the measure of its weight; or, more
exactly, the least limit of weight which will
suffice to maintain such height of atmos-
phere. The nucleus is usually so closely
surrounded by the dense mist that it's diam
eter cannot be measured; but at times the
mist rises, uncovers the nucleus and leaves
it with a sharp stellar aspect. The least
diameter determined at such times may be
larger than the actual one, but cannot be
smaller. From the combination of mass
and diameter the density of the nucleus can
be computed. In the case of Donati's
comet the diameter of the nuclens was per-
haps not more than hundred miles, while
the height of the atmosphere extended to
eighteen thousand miles. You may be sur
prised to learn that the corresponding den
sity of the nucleus was at least equal to that
of iron. What an unexpected contrast is
here presented to the prevalent notions con-
cerning the sun and the comets! The solid
sun is reduced by the science to the state OF
gas, while the substance of the ethereal
comet is solid and heavy metal.
In it's approach to the sun, the surface o.
the nucleaus is rapidly heated; it is melted
and vaporzed and subjected to frequent ex
plosions; the vapor rises in it's atmosphere
/ with we'll defined upper surface, which il