speedily followed, in 1826, by that of another, Biela's comet, whose period
of revolution is 6 3/4th years, and which is likewise planetary, having its
aphelion beyond the orbit of Jupiter, but within that of Saturn. It has a
fainter light than Encke's comet, and, like the latter, its motion is
direct, while Halley's comet moves in a course opposite to that pursued by
the planets. Biela's comet presents the first certain example of the orbit
of a comet intersecting that of the Earth. This position, with reference to
our planet, may therefore be productive of danger, if we can associate an
idea of danger with so extraordinary a natural phenomenon, whose history
presents no parallel, and the results of which we are consequently unable
correctly to estimate. Small masses endowed with enormous velocity may
certainly exercise a considerable power; but Laplace has shown that the mass
of the comet of 1770 is probably not equal to 1/5000th that of the Earth, or
about 1/2000th that of the Moon.*
[footnote] *Laplace, 'Expos. du Syst. du Monde', p. 216, 237.
We must not confound the passage of Biela's comet through the Earth's orbit
with its proximity to, or collision with our globe. When this passage took
place, on the 29th of October, 1832, it required a full month before the
Earth would reach the point of intersection of the two orbits. These two
comets of short periods of revolution also intersect each other, and it has
been justly observed,* that amid the many perturbations experienced by such
small bodies from the largr planets, there is a 'possibility' -- supposing a
meeting of these comets to occur in October -- that the inhabitants of the
Earth may witness the extraordinary spectacle of an encounter between two
cosmical bodies, and possibly of their reciprocal penetration and
amalgamation, or of their destruction by means of exhausting emanations.
[footnote] *Littrow, 'Beschreibende Astron.', 1835, s. 274. On the inner
comet recently discovered by M. Faye, at the Observatory of Paris, and whose
eccentricity is 0.551, its distance at its perihelion 1.690, and its
distance at its aphelion 5.832, see Schumacher, 'Astron. Nachr.', 1844, No.
495. Regarding the supposed identity of the comet of 1766 with the third
comet of 1819, see 'Astr. Nachr.', 1833, No. 239; and on the identity of the
comet of 1743 and the fourth comet of 1819, see No. 237 or the last
mentioned work.
Events of this nature, resulting either from deflection occasioned by
disturbing masses or primevally intersecting orbits, must have been of
frequent occurrence in the course of millions of years in the immeasurable
regions of ethereal space; but they must be regarded as isolated
occurrences, exercising no more general or alternative effects on cosmical
relations than the breaking forth or extinction of a volcano within the
limited sphere of our Earth.
A third interior comet, having likewise a short period of revolution was
discovered by Faye on the 22d of November, 1843, at the Observatory at
Paris. Its elliptic path, which approaches much more nearly to a circle
than that of any other known comet, is included within the orbits of Mars
and Saturn. This comet, therefore, which, according to Goldschmidt, passes
beyond the orbit of Jupiter, is one of the few whose perihelia are beyond
Mars. Its period of revolution is 7 29/100 years, and it is not improbable
that the form of its present orbit may be owing to its great approximation
to Jupiter at the close of the year 1839.
If we consider the comets in their inclosed elliptic orbits as members of
our solar system, and with respect to the length of their major axes, the
amount of their eccentricity, and their periods of revolution, we shall
probably find that the three planetary comets of Encke, Biela, and Faye are
most nearly approached in these respects, first, by the comet discovered in
1766 by Messier, and which is regarded by Clausen as identical with the
third comet of 1819; and next, by the fourth comet of the last-mentioned
year, discovered by Blaupain, but considered by Clausen as identical with
that of the year 1743, and whose orbit appears, like that of Lexell's comet,
to have suffered great variations from the proximity and attraction of
Jupiter. The two last-named comets would likewise seem to have a period of
revolution not exceeding five or six years, and their aphelia are in the
vicinity of Jupiter's orbit. Among the comets that have a period of
revolution of from seventy to
p 109
seventy-six years, the first in point of importance with respect to
theoretical and physical astronomy is Halley's comet, whose last appearance,
in 1835, was much less brilliant than was to be expected from preceding
ones; next we would notice Olbers's comet, discovered on the 6th of March,
1815; and, lastly, the comet discovered by Pons in the year 1812, and whose
elliptic orbit has been determined by Encke. The two latter comets were
invisible to the naked eye. We now know with certainty of nine returns of
Halley's large comet, it having recently been proved by Laugier's
calculations*, that in the Chinese table of comets, first made known to us
by Edward Biot, the comet of 1378 is identical with Halley's; its periods of
revolution have varied in the interval between 1378 and 1835 from 74.91 to
77.58 years, the mean being 76.1.
[footnote] *Laugier, in the 'Comptes Rendus des Seances de l'Academie',
1843, t. xvi., p. 1006.
A host of other comets may be contrasted with the cosmical bodies of which
we have spoken, requiring several thousand years to perform their orbits,
which it is difficult to determine with any degree of certainty. The
beautiful comet of 1811 requires, according to Argelander, a period of 3065
years for its revolution, and the colossal one of 1680 as much as 8800
years, according to Encke's calculation. These bodies respectively recede,
therefore, 21 and 44 times further than Uranus from the Sun, that is to say,
33,600 and 70,400 millions of miles. At this enormous distance the
attractive force of the Sun is still manifested; but while the velocity of
the comet of 1680 at its perihelion is 212 miles in a second, that is,
thirteen times greater than that of the Earth, it scarcely moves ten feet in
the second when at its aphelion. This velocity is only three times greater
than that of water in our most sluggish European rivers, and equal only to
half that which I have observed in the Cassiquiare, a branch of the Orinoco.
It is highly probable that, among the innumerable host of uncalculated or
undiscovered comets, there are many whose major axes greatly exceed that of
the comet of 1680. In order to form some idea by numbers, I do not say of
the sphere of attraction, but of the distance in space of a fixed star, or
other sun, from the aphelion of the comet of 1680 (the furthest receding
cosmical body with which we are acquainted in our solar system), it must be
remembered that, according to the most recent determinations of parallaxes,
the nearest fixed star is full 250 times further removed from our sun than
the comet in its aphelion. The comet's distance is only 44
p 110
times that of Uranus, while 'a' Centauri is 11,000 and 61 Cygni 31,000 times
that of Uranus, according to Bessel's determinations.
Having considered the greatest distances of comets from the central body, it
now remains for us to notice instances of the greatest proximity hitherto
measured. Lexell and Burckhardt's comet of 1770, so celebrated on account
of the disturbances it experienced from Jupiter, has approached the Earth
within a smaller distance than any other comet. On the 28th of June, 1770,
its distance from the Earth was ony six times than of the Moon. The same
comet passed twice, viz., in 1769 and 1779, through the system of Jupiter's
four satellites without producing the slightest notable change in the
well-known orbits of these bodies. The great comet of 1680 approached at
its perihelion eight or nine times nearer to the surface of the Sun than
Lexell's comet did to that of our Earth, being on the 17th of December a
sixth part of the Sun's diameter, or seven tenths of the distance of the
Moon from that luminary. Perihelia occurring beyond the orbit of Mars can
seldom be observed by the inhabitants of the Earth, owing to the faintness
of the light of distant comets; and among those already calculated the comet
of 1729 is the only one which has its perihelion between the orbits of
Pallas and Jupiter; it was even observed beyond the latter.
Since scientific knowledge, although frequently blended with vague and
superficial views, has been more extensively diffused through wider circles
of social life, apprehensions of the possible evils threatened by comets
have acquired more weight as their direction has become more definite. The
certainty that there are within the known planetary orbits comets which
revisit our regions of space at short intervals -- that great disturbances
have been produced by Jupiter and Saturn in their orbits, by which such as
were apparently harmless have been converted into dangerous bodies -- the
intersection of the Earth's orbit by Biela's comet -- the cosmical vapor,
which, acting as a resisting and impeding medium, tends to contract all
orbits -- the individual difference of comets, which would seem to indicate
considerable decreasing gradations in the quantity of the mass of the
nucleus, are all considerations more than equivalent, both as to number and
variety, to the vague fears entertained in early ages of the general
conflagration of the world by 'flaming swords', and stars with 'fiery
streaming hair'. As the consolatory considerations which may be derived
from the calculus of probabilities address themselves to reason and to
p 111
meditative understanding only, and not to the imagination or to a desponding
condition of mind, modern science has been accused, and not entirely without
reason, of not attempting to allay apprehensions which it has been the very
means of exciting. It is an inherent attribute of the human mind to
experience fear, and not hope or joy, at the aspect of that which is
unexpected and extraordinary.*
[footnote] *Fries, 'Vorlesungen uber die Sternkunde', 1833, s. 262-267
(Lectures on the Science of Astronomy). An infelicitously chosen instance
of the good omen of a comet may be found in Seneca, 'Nat. Quest.', vii., 17
and 21. The philosopher thus writes of the comet: "Quem nos Neronis
principatu latissimo vidimus et qui cometis detraxit infamiam."
The strange form of a large comet, its faint nebulous light, and its sudden
appearance in the vault of heaven, have in all regions been almost
invariably regarded by the people at large as some new and formidable agent
inimical to the existing state of things. The sudden occurrence and short
duration of the phenomenon lead to the belief of some equally rapid
reflection of its agency in terrestrial matters, whose varied nature renders
it easy to find events that may be regarded as the fulfillment of the evil
foretold by the appearance of these mysterious cosmical bodies. In our own
day, however, the public mind has taken another and more cheerful, although
singular, turn with regard to comets; and in the German vineyards in the
beautiful valleys of the Rhine and Moselle, a belief has arisen, ascribing
to these once ill-omened bodies a beneficial influence on the ripening of
the vine. The evidence yielded by experience, of which there is no lack in
these days, when comets may so frequently be observed, has not been able to
shake the common belief in the meteorological myth of the existence of
wandering stars capable of radiating heat.
This material taken from pages 111- 147
COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1
by Alexander von Humboldt
Translated by E C Otte
from the 1858 Harper & Brothers edition of Cosmos, volume 1
--------------------------------------------------
From comets I would pass to the consideration of a far more enigmatical
class of agglomerated matter -- the smallest of all asteroids, to which we
apply the name 'aërolites', or 'meteoric stones',* when they reach our
atmosphere in a fragmentary condition.
[footnote] * (Much valuable information may be obtained regarding the
origin and composition of aërolites or meteoric stones in Memoirs on the
subject, by Baumbeer and other writers, in the numbers of Poggendorf's
'Annalen', from 1845 to the present time.) -- Tr.
If I should seem to dwell on the specific enumeration of these bodies, and
of comets, longer than the general nature of this work might warrant, I have
not done so undesignedly. The diversity existing in the individual
characteristics of comets has already been noticed. The imperfect knowledge
we possess of their physical character renders it
p 112
diifficult in a work like the present, to give the proper degree of
circumstantiality to the phenomena, which, although of frequent recurrence,
have been observed with such various degrees of accuracy, or to separate the
necessary from the accidental. It is only with respect to measurements and
computations that the astronomy of comets has made any marked advancement,
and, consequently, a scientific consideration of these bodies must be
limited to a specification of the differences of physiognomy and
conformation in the nucleus and tail, the instances of great approximation
to other cosmical bodies, and of the extremes in the length of their orbits
and in their periods of revolution. A faithful delineation of these
phenomena, as well as of those which we proceed to consider, can only be
given by sketching individual features with the animated circumstantiality
of reality.
Shooting stars, fire-balls, and meteoric stones are, with great probability,
regarded as small bodies moving with planetary velocity, and revolving in
obedience to the laws of general gravity in conic sections round the Sun.
When these masses meet the Earth in their course, and are attracted by it,
they enter within the limits of our atmosphere in a luminous condition, and
frequently let fall more or less strongly heated stony fragments, covered
with a shining black crust. When we enter into a careful investigation of
the facts observed at those epochs when showers of shooting stars fell
periodically in Cumana in 1799, and in North America during the years 1833
and 1834, we shall find that 'fire-balls' can not be considered separately
from shooting stars. Both these phenomena are frequently not only
simultaneous and blended together, but they likewise are often found to
merge into one another, the one phenomenon gradually assuming the character
of the other alike with respect to the size of their disks, the emanation of
sparks, and the velocities of their motion. Although exploding smoking
luminous fire-balls are sometimes seen, even in the brightness of tropical
daylight,* equaling in size the apparent
p 113
diameter of the Moon, innumerable quantities of shooting stars have, on the
other hand, been observed to fall in forms of such extremely small
dimensions that they appear only as moving points or 'phosphorescent
lines.'**
[footnote] *A friend of mine, much accustomed to exact trigonometrical
measurements, was in the year 1788 at Popayan, a city which is 2 degrees 26'
north latitude, lying at an elevation of 5583 feet above the level of the
sea, and at noon, when the sun was shining brightly in a cloudless sky, saw
his room lighted up by a fire-ball. He had his back to the window at the
time, and on turning round, perceived that great part of the path traversed
by the fire-ball was still illuminated by the brightest radiance. Different
nations have had the most various terms to express these phenomena: The
Germans use the word 'Sternschnuppe', literally 'star snuff' -- an
expression well suited to the physical views of the vulgar in former times,
according to which, the lights in the firmament were said to undergo a
process of 'snuffing' or cleaning; and other nations generally adopt a term
expressive of a 'shot' or 'fall' of stars, as the Swedish 'stjernifall', the
Italian 'stella cadente', and the English 'star shoot.' In the woody
district of the Orinoco, on the dreary banks of the Cassiquiare, I heard the
natives in the Mission of Vasiva use terms still more inelegant than the
German 'star snuff.' ('Relation Historique du Voy. aux Régions Equinox.',
t. ii., p. 513.) These same tribes term the pearly drops of dew which cover
the beautiful leaves of the heliconia 'star spit.' In the Lithuanian
mythology, the imagination of the people has embodied its ideas of the
nature and signification of falling stars under nobler and more graceful
symbols. The Parcæ, 'Werpeja', weave in heaven for the new-born child its
thread of fate, attaching each separate thread to a star. When death
approaches the person, the thread is rent, and the star wanes and sinks to
the earth. Jacob Grimm, 'Deutsche Mythologie', 1843, s. 685.
[footnote] ** According to the testimony of Professor Denison Olmsted, of
Yale College, New Haven, Connecticut. (See Poggend., 'Annalen der Physik',
bd. xxx., s. 194.) Kepler, who excluded fire-balls and shooting stars from
the domain of astronomy, because they were, according to his views, "meteors
arising from the exhalations of the earth, and blending with the higher
ether," expresses himself, however, generally with much caution. He says:
"Stellæ cadentes sunt materia viscida inflammata. Earum aliquæ inter
cadendum absumuntur, aliquæ verè in terram cadunt, pondere suo tractæ.
Nec est dissimile vero, quasdam conglobatas esse ex materia fæculentâ, in
ipsam auram ætheream immixta: exque aëtheris regione, tractu rectilineo,
per aërem trajicere, ceu minutos competas, occultâ causa motus
utrorumque." -- Kepler, 'Epit. Astron. Copernicanæ', t. i., p. 80.
It still remains undertermined whether the many luminous bodies that shoot
across the sky may not vary in their nature. On my return from the
equinoctial zones, I was impressed with an idea that in the torrid regions
of the tropics I had more frequently than in our colder latitudes seen
shooting stars fall as if from a height of twelve or fifteen thousand feet;
that they were of brighter colors, and left a more brilliant line of light
in their track; but this impression was no doubt owing to the greater
transparency of the tropical atmosphere*, which enables the eye to penetrate
further into distance.
[footnote] *'Relation Historique', t. i., p. 80, 213, 527. If in falling
stars, as in comets, we distinguish between the head or nucleus and the
tail, we shall find that the greater transparency of the atmosphere in
tropical climates is evinced in the greater length and brilliancy of the
tail which may be observed in those latitudes. The phenomenon is therefore
not necessarily more frequent there, because it is oftener seen and
continues longer visible. The influence exercised on shooting stars by the
character of the atmosphere is shown occasionally even in our temperate
zone, and at very small distances apart. Wartmann relates that on the
occasion of a November phenomenon at two places lying very near each other,
Geneva and Aux Planchettes, the number of the meteors counted were as 1 to
7. (Wartmann, 'Mém. sur les Etoiles filantes', p. 17.) The tail of a
shooting star (or its 'train'), on the subject of which Brandes has made so
many exact and delicate observations, is in no way to be ascribed to the
continuance of the impression produced by light on the retina. It sometimes
continues visible a whole minute, and in some rare instances longer than the
light of the nucleus of the shooting star; in which case the luminous track
remains motionless. (Gilb., 'Ann.', bd. xiv., s. 251.) This circumstance
further indicates the analogy between large shooting stars and fire-balls.
Admiral Krusenstern saw, in his voyage round the world, the train of a
fire-ball shine for an hour after the lluminous body itself had disappeared,
and scarcely move throughout the whole time. ('Reise', th. i., s. 58.) Sir
Alexander Burnes gives a charming description of the transparency of the
clear atmosphere of Bokhara, which was once so favorable to the pursuit of
astronomical observations. Bokhara is situated in 39 degrees 48' north
latitude, and at an elevation of 1280 feet above the level of the sea.
"There is a constant serenity in its atmosphere, and an admirable clearness
in the sky. At night, the stars have uncommon luster, and the Milky Way
shines gloriously in the firmament. There is also a never-ceasing display
of the most brilliant meteors, which dart like rockets in the sky; ten or
twelve of them are sometimes seen in an hour, assuming every color -- fiery
red, blue, pale, and faint. It is a noble country for astronomical science,
and great must have been the advantage enjoyed by the famed observatory of
Samarkand." (Burnes, 'Travels into Bokhara', vol. ii. (1834), p. 158.) A
mere traveler must not be reproached for calling ten or twelve shooting
stars in an hour "many," since it is only recently that we have learned,
from careful observations on this subject in Europe, that eight is the mean
number which may be seen in an hour in the field of vision of one individual
(Quetelet, 'Corresp. Mathém.', Novem., 1837, p. 447); this number is,
however, limited to five or six by that diligent observer, Olbers. (Schum.,
'Jahrb.', 1838, s. 325.)
p 114
Sir Alexander Burnes likewise extols as a consequence of the purity of the
atmosphere in Bokhara the enchanting and constantly-recurring spectacle of
variously-colored shooting stars.
The connection of meteoric stones with the grander phenomenon of fire-balls
-- the former being known to be projected from the latter with such force as
to penetrate from ten to fifteen feet into the earth -- has been proved,
among many other instances, in the falls of azzzuerolites at Barbotan, in
the Department des Landes (24th July, 1790), at Siena (16th June, 1794), at
Weston, in Connecticut, U. S. (14th December, 1807), and at Juvenas in the
Department of Ardèche (14th June, 1821). Meteoric stones are in some
instances thrown from dark clouds suddenly formed in a clear sky, and fall
with a noise resembling thunder. Whole districts have thus occasionally
been covered with thousands of fragmentary masses, of uniform character but
unequal magnitudes, that
p 115
have been hurled from one of these moving clouds. In less frequent cases,
as in that which occurred on the 16th of September, 1843, at Kleinwenden,
near Mühilhausen, a large aërolite fell with a thundering crash while the
sky was clear and cloudless. The intimate affinity between fire-balls and
shooting stars is further proved by the fact that fire-balls, from which
meteoric stones have been thrown have occasionally been found, as at Angers,
on the 9th of June, 1822, having a diameter scarcely equal to that of the
small fire-works called Roman candles.
The formative power, and the nature of the physical and chemical processes
involved in these phenomena are questions all equally shrouded in mystery,
and we are as yet ignorant whether the particles composing the dense mass of
meteoric stones are originally, as in comets, separated from one another
when they become luminous to our sight, or whether in the case of smaller
shooting stars, any compace substance actually falls, or, finally, whether a
meteor is composed only of a smoke-like dust, containing iron and nickel;
while we are wholly ignorant of what takes place within the dark cloud from
which a noise like thunder is often heard for many minutes before the stones
fall.*