_METEORS AND METEORIC OBSERVATIONS._
Ancient ideas concerning Meteors.—Meteoric
Apparitions.—Radiation of Meteors.—Identity of Meteors
and Comets.—Aerolites.—Fireballs.—Differences of
Motion.—Nomenclature of Meteor-Systems.—Meteor-Storms.—Telescopic
Meteors.—Meteor-Showers.—Varieties of Meteors.—Heights.—Meteoric
Observations.
“As oft along the still and pure serene
At nightfall, glides a sudden trail of fire,
Attracting with involuntary heed
The eye to follow it, erewhile it rest;
And seems some star that shifted place in heaven.”
DANTE.
No one can contemplate the firmament for long on a clear moonless
night without noticing one or more of those luminous objects called
shooting-stars. They are particularly numerous in the autumnal months,
and will sometimes attract special attention either by their frequency
of apparition or by their excessive brilliancy in individual cases.
For many ages little was known of these bodies, though some of the
ancient philosophers appear to have formed correct ideas as to their
astronomical nature. Humboldt says that Diogenes of Apollonia, who
probably belonged to the period intermediate between Anaxagoras and
Democritus, expressed the opinion that, “together with the visible
stars, there are invisible ones which are therefore without names.
These sometimes fall upon the Earth and are extinguished, as took place
with the star of stone which fell at Ægos Potamoi.” Plutarch, in the
‘Life of Lysander,’ remarks:—“Falling stars are not emanations or
rejected portions thrown off from the ethereal fire, which when they
come into our atmosphere are extinguished after being kindled: they
are, rather, celestial bodies which, having once had an impetus of
revolution, fall, or are cast down to the Earth, and are precipitated,
not only on inhabited countries, but also, and in greater numbers,
beyond these into the great sea, so that they remain concealed.”
In later times, however, opinions became less rational. Falling stars
were considered to be of a purely terrestrial nature, and originated by
exhalations in the upper regions of the air. Shakespeare expressed the
popular belief when he wrote:—
“I shall fall
Like a bright exhalation in the evening,
And no man see me more.”
Another theory, attributed to Laplace, Arago, and others, was that
meteors were ejections from lunar volcanoes. But these explanations
were not altogether satisfactory in their application. The truth is,
that men had commenced to theorize before they had begun to observe and
accumulate facts. They had learnt little or nothing as to the numbers,
directions, and appearances of meteors, and therefore possessed no
materials on which to found any plausible hypothesis to account for
them.
_Meteoric Apparitions._—The occasional apparition of brilliant
detonating fireballs, the occurrence of remarkable star-showers, the
precipitation upon the Earth’s surface of stony masses, were facts
which could be verified from many independent sources, and they set
men thinking how to account for the strange and startling freaks of
nature as exhibited in such phenomena. But though records existed of
exceptionally large meteors and of meteor-showers, the descriptions
were imperfect and failed in the most important details. The observers
were usually unprepared for witnessing such events, and gave
exaggerated and inaccurate accounts of what they had seen. The vivid
brightness of a fireball (overpowering the lustre of the stars, and
even vieing with the Moon in splendour), the flaming train left in its
wake (curling itself up into grotesque shapes, as it drifted and died
away), the form of the nucleus with its jets and sparks, and the final
explosion, with the reverberations it caused, were all alluded to by
the enthusiastic observer; but it was only in rare cases that the more
valuable features were placed on record. The _direction_ and _duration_
of the meteor’s flight amongst the stars were facts of greater
significance than the mere visible aspect of the object; but they were
seldom regarded. Hence the early observations proved of little weight
in inducing just conceptions as to the phenomena of meteors.
There is, perhaps, no celestial event which can compare, as regards
its striking aspect and interesting features, with that of a meteoric
display of the most brilliant kind. A large comet, a total solar
eclipse, a bright display of aurora, have each their attractive and
imposing forms; but the effect produced is hardly equal to that during
the Earth’s _rencontre_ with a dense meteor-swarm. The firmament
becomes alive with shooting-stars of every magnitude; their incessant
flights are directed to every point of the compass for several hours;
and the scene is so animated, and one of such peculiarly impressive and
novel character, that it can never be forgotten by those who have been
among its fortunate spectators.
_Radiation of Meteors._—Heis, in Germany, was the pioneer in this
branch of practical astronomy. About half a century ago he began
systematic observations, and gathered many useful data. Schmidt, at
Bonn and Athens, followed his example; and in England Prof. Alexander
Herschel and Mr. R. P. Greg devoted themselves to the subject with
highly successful results. Their collective labours revealed a large
number of well-defined systems of meteors, and enabled them to publish
tables of the radiant-points. The investigations were more precise than
formerly, and conducted on methods ensuring more accurate and plentiful
materials. The radiation of meteors from fixed points in the sky had
been observed before in regard to the great display which occurred
in November 1833; but the meteors that fell on ordinary nights were
regarded as sporadic, until Heis and his immediate successors showed
they were reducible to an orderly arrangement and that every one of
them had its radiant-point and its origin in a definite meteor-stream.
The apparently divergent flights from a common centre are simply due
to the effects of perspective on bodies really moving in parallel
directions and collected into groups more or less scattered.
[Illustration: Fig. 52.
Radiation of Meteors
(Shower of early Perseids from 32°+53°, July 28-Aug. 1, 1878.)]
_Identity of Meteors and Comets._—The mystery concerning these
fugitive objects and their vagaries of appearance was not always to
remain concealed. Denison Olmsted had, in his work on ‘The Mechanism
of the Heavens,’ published in 1850, stated that the constitution of
the body to which the meteors of 1833 belonged bore “a strong analogy
to comets.” Reichenbach, in 1858, wrote a paper in which it was sought
to prove that a comet is a swarm of meteorites. Prof. Kirkwood, in
1861, also concluded that “meteors and meteoric rings are the debris
of ancient but now disintegrated comets, whose matter has become
distributed around their orbits.” But it remained for Schiaparelli, of
Milan, in 1866, to demonstrate the identity of meteoric and cometary
systems. Others had reasoned up to it, and observers had amassed many
useful observations bearing on the subject; but absolute proof was
wanting until Schiaparelli supplied it. He computed elements for a
well-known shower of meteors occurring on August 10th, and found the
orbit presented a very close resemblance to that of Comet III. 1862;
and he detected a similar analogy between the November meteors and
Comet I. 1866. The orbit of the April meteors was afterwards shown
by Galle and Weiss to agree with the path of Comet I. 1861; and a
meteor-shower occurring at the end of November was found to coincide
with Biela’s Comet. Facts like these could not be disproved. Comets
were thenceforth known to be the parents—the derivative source—of
meteors. Thus two important classes of objects became as one, the
differences observed being merely those of aspect due to the variable
conditions under which they were presented. The great meteor-shower of
November was found to be the dispersed materials of Tempel’s Comet of
1866 seen in detail and from a near standpoint. Every meteoric display
was known to be the visible effects of the collision of the Earth with
a comet or with the great stream of planetary fragments describing a
cometary orbit.
[Illustration: Fig. 53.
1. Double meteor, Dec. 29, 1886. 2. Curved meteor, Dec. 25, 1886.
3. Fireball, Sept. 7, 1888.
]
[Illustration: Fig. 54.
Meteorite found in Chili in 1866.]
[Illustration: Fig. 55.
Meteorite which fell at Orgueil in 1864.]
_Aerolites._—Meteors enter our atmosphere with such great velocity
that the friction induced by their impact is sufficient to destroy
them by combustion. They rarely approach the Earth’s surface within 15
miles. Occasionally, however, a slow-moving meteor of large size, and
formed of a very compact substance, will penetrate entirely through the
air-strata and fall upon the Earth’s surface. Many instances of the
kind have been recorded, and a few of these are quoted below:—
1478 B.C. The Parian chronicle records that an aerolite or
thunder-stone fell in the island of Crete. This appears to be the
earliest stone-fall described in history.
654 B.C. A shower of stones descended near Rome.
465 B.C. A stone, surrounded with fire, fell in Thrace. This stone is
referred to by several ancient writers. It was termed the “Mother of
the Gods” and is said to have fallen at the feet of the poet Pindar.
52 B.C. A shower of iron descended at Lucania, in the time of Crassus.
1492 A.D. A stone weighing 262 lb. fell at Ensisheim, in Alsace.
1642. A stone of 4 lb. fell near Woodbridge, in Suffolk.
1795, Dec. 13. A stone of 56 lb. fell at Wold Cottage, Thwing,
Yorkshire.
1860, July 14. A shower of aerolites fell at Dhurmsala, in India. A
tremendous detonation attended their descent, and the natives became
greatly alarmed. They supposed the stones to have been thrown by some
of their deities from the summit of the Himalayas, and many of them
were preserved as objects of religious veneration.
1864, May 14. A very large meteor was observed in France. At Montauban
and the neighbourhood deafening explosions occurred, and showers of
stones fell near the villages of Orgueil and Nohic.
1876, April 20. A piece of iron weighing 7-3/4 lb. fell at Rowton,
Shropshire.
1881, March 14. A stone weighing 3 lb. 8-1/4 oz. fell at
Middlesborough, Yorkshire, on a part of the North-Eastern Railway
Company’s branch line. The descent of the aerolite was witnessed by an
inspector and three platelayers, who were working about fifty yards
distant. At first they became aware of a whizzing or rushing noise in
the air, immediately followed by the sudden blow of a body striking
the ground near. The hole, 11 inches deep, which the stone made was
found directly after, and the stone was extracted.
Many other examples might be given, but the above will be sufficient
for our purpose. Records of this nature were discredited in former
times; but more modern researches have long since placed their reality
beyond all question. The fall of stones from the sky is no longer
regarded as a mere legendary tale, but as one of the well-assured
operations of nature.
Meteoric stones and irons have been classified according to the
ingredients of their composition. Those in which iron is found in
considerable amount are termed siderites, those containing an admixture
of iron and stone, siderolites, and those consisting almost entirely of
stone are known as aerolites. The siderite which fell in Shropshire on
April 20, 1876, forms only the seventh recorded instance where a mass
of meteoric iron has been actually seen to fall.
_Fireballs._—The table on p. 268 gives the dates, heights, &c. of
fifteen fireballs observed during the last quarter of a century.
Fireballs are sometimes detonating, though more often silent. The
fireball of Nov. 23, 1877, gave a sound like salvoes of artillery,
and doors and windows were shaken violently. At Chester the noise of
its explosion was compared to loud but distant thunder. Lieut.-Col.
Tupman says that “thunder, to be loud, must be within five miles;
hence it appears that the violence of the explosion must have been at
least a hundred times greater than a peal of thunder, the intensity of
sound-waves diminishing as the square of the distance.” “The explosion
of a 13-inch bomb-shell, consisting of some 200 lb. of iron, would not
have produced a sound of one hundredth part of the intensity of the
meteor-explosion.” This fireball must therefore have been an object of
considerable mass before its dissolution; and it is fortunate that such
bodies are usually destroyed by the effects of combustion before they
reach the Earth’s surface.
These phenomena exhibit many varieties of appearance.
+——————————————+——————+————————————————————+————————+——————+
| | | Height. | Real | |
| Date of | +——————————+————————-+ Length |Velo- |
| Apparition. |G.M.T.| At Ap- |At Disap-|of Path.|city. |
| | |pearance. |pearance.| | |
+——————————————+——————+————————————————————+————————+——————+
| | h m| miles. | miles. | miles. |miles.|
|1865, April 29| 12 42| 52 | 37 | 75 |20 |
|1868, Sept. 5| 8 5| 250 | 85 | 1200 |28 |
|1869, Nov. 6| 6 50| 90 | 27 | 170 |35 |
|1872, July 22| 8 55| 77 | 37 | 88 | |
|1874, Aug. 10| 11 53| 77 | 33 | 105 |17 |
|1875, Sept. 3| 9 55| 75 | 40 | 35 |27 |
|1875, Sept. 14| 8 28| 52 | 13 | 104 |13 |
|1876, Sept. 24| 6 30| 58 | 16 | 45 |15 |
|1877, Nov. 23| 8 25| 95 | 14 | 135 |17½ |
|1878, June 7| 9 53| 65 | 37 | 160 |19 |
|1879, Feb. 23| 14 53| 60 | 7 | 102 |14½ |
|1886, Nov. 17| 7 18| 96 | 21 | 123 |17½ |
|1887, May 8| 8 22| 70 | 14 | 110 |18 |
|1888, Aug. 13| 11 33| 78 | 47 | 46 | |
|1889, May 29| 10 44| 58 | 23 | 76 | 8½ |
+——————————————+——————+————————————————————+————————+——————+
+——————————————+————————-+————————————————+
| |Radiant- | |
| Date of | Point. | |
| Apparition. | | Authority. |
| |R.A. Dec.| |
+——————————————+————————-+————————————————+
| | ° ° | |
|1865, April 29| 73 +47 |A. S. Herschel. |
|1868, Sept. 5| 14 -2 |G. von Niessl. |
|1869, Nov. 6| 62 +37 |A. S. Herschel. |
|1872, July 22|246 -11 |T. H. Waller. |
|1874, Aug. 10|325 -17 |W. H. Wood. |
|1875, Sept. 3|311 +52 |G. L. Tupman. |
|1875, Sept. 14|348 -0 |G. L. Tupman. |
|1876, Sept. 24|285 +35 |A. S. Herschel. |
|1877, Nov. 23| 62 +21 |G. L. Tupman. |
|1878, June 7|247 -25 |A. S. Herschel. |
|1879, Feb. 23|310 +55 |J. E. Clark. |
|1886, Nov. 17| 34 +19 |W. F. Denning. |
|1887, May 8|191 -5 |W. F. Denning. |
|1888, Aug. 13| 43 +56 |W. F. Denning. |
|1889, May 29|216 7 |D. Booth. |
+——————————————+————————-+————————————————+
[Illustration: Fig. 56.
Fireball of Nov. 23, 1877, 8^h 24^m, emerging from behind a cloud.
(Drawn by J. Plant, Salford.)]
Sometimes there is no visible explosion; the bright nucleus slowly
dies out until reduced to a faint spark before final disappearance.
Several outbursts of light are often noted; and a curious halting
motion has been observed in regard to large slow-moving meteors. I have
occasionally remarked a succession of four brilliant flashes given by
individual fireballs. These flashes, though sometimes of startling
intensity, are somewhat different to the transient vividness of
lightning; they come more softly, and remind one forcibly of moonlight
breaking suddenly from the clear intervals in passing clouds.
Fireballs differ vastly from shooting-stars in point of size; but their
origin is identical. The August meteor-shower yields the smallest
shooting-stars and the largest type of fireballs. The great display of
meteors on Nov. 27, 1885, not only presented us with large and small
members, but it also furnished us with a siderite or piece of iron,
presumably from Biela’s Comet. This fell at Mazapil, Mexico; and as
considerable interest is attached to the case, I quote a part of the
discoverer’s statement:—
“It was at about 9 o’clock on the night of November 27th, when I went
out to the corral to feed certain horses: suddenly I heard a loud
sizzing noise, exactly as though something red-hot was being plunged
into cold water; and almost instantly there followed a somewhat loud
thud. At once the corral was covered with a phosphorescent light;
while suspended in the air were small luminous sparks, as though from
a rocket.... A number of people came running towards me; and when we
had recovered from our fright we saw the light disappear, and bringing
lanterns to look for the cause found a hole in the ground, and in it a
ball of light. We retired to a distance, fearing it would explode and
harm us. Looking up to the sky, we saw from time to time exhalations of
stars, which soon went out without noise. We returned after a little,
and found in the hole a hot stone which we could barely handle; this,
on the next day, we saw looked like a piece of iron. All night it
rained stars; but we saw none fall to the ground, as they all seemed to
be extinguished while yet very high up.”
This is the first observed instance in which a meteorite has actually
reached the Earth’s surface during the progress of a star-shower.
If its identity with the meteors of Biela’s Comet is admitted, then
all classes of meteoric phenomena would appear to have a community of
origin.
_Differences of Motion._—Great differences are observed in the velocity
of meteors. An observer may notice all varieties on the same night
of observation. Some will move very slowly, others shoot quickly
across the sky. These differences are occasioned by the astronomical
conditions affecting the position of the meteor-orbit relatively to
the motion of the Earth. Thus the meteors of Nov. 13 move with great
velocity (44 miles per second), because they come directly from that
part of the heavens towards which the Earth is moving; hence the
orbital speed of the Earth (18½ miles per second) and meteors (26 miles
per second) is combined in the observed effects. But in the case of
the meteor-shower of Nov. 27 the motions are extremely slow (about 10
miles per second), as the Earth and the meteors are travelling nearly
parallel in the same direction, and the latter have to overtake the
Earth.
_Nomenclature of Meteor-Systems._—It is customary to name the showers
after the constellation from which the meteors appear to diverge. Thus
the meteors of April 20 are called _Lyrids_, the radiant being in Lyra;
the meteors of August 10 are termed _Perseids_, the point of emanation
being in Perseus. The two great streams of November are known as the
_Leonids_ (13th) and _Andromedes_ (27th). Several showers are often
visible in the same constellation; and when it is desired to name these
according to the above system, it is necessary to add the approximate
star to distinguish them. Thus, in August there are showers of μ
Perseids, ε Perseids, and α Perseids, in addition to the well-known
Perseids of August 10.
_Meteor-Storms._—On Nov. 12, 1799, Humboldt, at Cumana, in South
America, saw “thousands of bolides and falling stars succeed each other
during four hours.” On Nov. 12, 1833, this shower recurred, and was
witnessed with magnificent effect in America. One observer stated that
between 4 and 6 A.M. (Nov. 13) about 1000 meteors per minute might
have been counted! Another display occurred on Nov. 13, 1866, and on
this occasion 8485 meteors were enumerated by several observers at
Greenwich. A different system gave us a brilliant exhibition on Nov.
27, 1872, when 33,000 meteors were counted by Denza and his assistants
at Moncalieri, in Italy, between the hours of 5^h 50^m and 10^h 30^m
P.M. A repetition of this phenomenon occurred on Nov. 27, 1885, when
the same observers counted nearly 40,000 meteors between 6^h and 10^h
P.M.
[Illustration: Fig. 57.
VERTICAL.
Flight of Telescopic Meteors seen by W. R. Brooks, Nov. 28, 1883.]
_Telescopic Meteors._—Observers who are engaged in seeking for comets
or studying variable stars employ low powers and large fields, and
during the progress of their work notice a considerable number of
small meteors. At some periods these bodies are more plentiful than
at others, and appear in such rapid succession that the observer’s
attention is distracted from the special work he is pursuing to
watch them more narrowly and record their numbers. Schmidt saw 146
telescopic meteors during ten years. They ranged between the 7th and
11th mags. Winnecke in the year 1854 noticed 105 of these objects
on thirty-two evenings of observation with a 3-inch finder, power
15, and field of 3°. I have also remarked many of these objects when
using the comet-eyepieces of my 10-inch reflector[45], and find they
are apparently more numerous than the ordinary naked-eye meteors
in the proportion of 22 to 1. It would be supposed from the great
rapidity with which the latter shoot across the firmament that the
smaller telescopic meteors are scarcely distinguishable by their
motion, as they must dart through the field instantaneously and only
be perceptible as lines of light. But this impression is altogether
inconsistent with the appearances observed. They possess no such
velocity, but usually move with extreme slowness, and not unfrequently
the whole of the path is comprised within the same field of view.
The eye is enabled to follow them as they leisurely traverse their
courses, and to note peculiarities of aspect. Of course, there are
considerable differences of speed observed, but as a rule the rate is
decidedly slow and far less than that shown by naked-eye meteors. I
believe that telescopic meteors are situated at great heights in the
atmosphere, and that their diminutive size and slowness of movement
are due to their remoteness. This conclusion will hardly be avoided
by anyone who attentively studies the several classes of meteors in
their various aspects. Unfortunately no attempt appears to have been
hitherto made to determine the actual heights of telescopic meteors,
owing to the difficulty of obtaining two reliable observations of the
same object. The only way of securing such data would be for several
observers to watch certain selected regions by prearrangement either
with a low-power telescope or field-glass, and record the exact times
and paths of the meteors seen. On a comparison of the results a good
double observation of the same object might be found, in which case the
real path could be readily computed.
Future observers should note the different forms of telescopic meteors.
Safarik has divided them into four classes, viz.:—(1) Well-defined
star-like objects of very small size; (2) Large luminous bodies of
some minutes of arc in diameter; (3) Well-defined disks of a very
perceptible diameter brighter at the border than at the centre, which
gives them the aspect of hollow transparent shells; and (4) faint
diffused masses of irregular shape, considerable size, and different
colours. He has seen hundreds of meteors of every magnitude from the
2nd down to the 12th pass through the field of his 6½-inch reflector
(ordinary power 32, field 54′). On Aug. 30, 1880, 9^h to 15^h he
observed between 50 and 100 telescopic meteors, and many others were
seen on the following night. Whenever a shower of these bodies, such
as that witnessed by Brooks on Nov. 28, 1883, occurs, observers should
notice whether the objects participate in a common direction of motion;
because, if so, the radiant-point will admit of determination. The
horary rate of their apparition ought also to be ascertained. Those
who habitually search for comets should invariably make a note of
telescopic meteors, as such records would aid inquiries into the
relative frequency of these phenomena.
_Meteor Showers._—The following short list includes the principal
displays of the year:—
+———————————————-+——————————————-+————————+——————————————-+——————————+
| Name of | Duration. |Date of | Radiant- | Sun’s |
| Shower. | | Max. | Point. |Longitude.|
+———————————————-+——————————————-+————————+——————————————-+——————————+
| | | | α δ | |
| | | | ° ° | ° |
|Quadrantids |Dec. 28-Jan. 4 |Jan. 2 | 229·8 +52·5 | 281·6 |
|Lyrids |April 16-22 |April 20| 269·7 +32·5 | 31·3 |
|η Aquarids |April 30-May 6 |May 6 | 337·6 - 2·1 | 46·3 |
|δ Aquarids |July 23-Aug. 25|July 28 | 339·4 -11·6 | 125·6 |
|Perseids |July 8-Aug. 22 |Aug. 10 | 45·9 +56·9 | 138·5 |
|Orionids |Oct. 9-29 |Oct. 18 | 92·1 +15·5 | 205·9 |
|Leonids |Nov. 9-17 |Nov. 13 | 150·0 +22·9 | 231·5 |
|Andromedes |Nov. 25-30 |Nov. 27 | 25·3 +43·8 | 245·8 |
|Geminids |Dec. 1-14 |Dec. 10 | 108·1 +32·6 | 259·5 |
+———————————————-+——————————————-+————————+——————————————-+——————————+
_Notes._
_Quadrantids._ Heis was the first to determine this radiant accurately.
It was subsequently observed by Masters and Prof. Herschel (1863-4).
The radiant is circumpolar in this latitude, but low down during the
greater part of the night, hence the display is usually seen to the
best advantage on the morning of Jan. 2.
_Lyrids._ Attention was first drawn to the April meteors by Herrick in
the United States. Active displays occurred in 1863 and 1884.
η _Aquarids._ Further observations are urgently required of this
stream. The radiant is only visible for a short time before sunrise.
There is a considerable difference between my results and those secured
by Lieut.-Col. Tupman, the discoverer of this system in 1870, whose
observations place the radiant at 326½—2½ April 29-May 3. These May
Aquarids are interesting from the fact that they present an orbital
resemblance to Halley’s Comet, which makes a near approach to the Earth
on May 4, twelve days before reaching the descending node.
δ _Aquarids._ The meteoric epoch, July 26-30, was first pointed out
by Quetelet many years ago. Biot also found, from the oldest Chinese
observations, a general maximum between July 18 and 27 (Humboldt).
Showers of Aquarids were remarked by Schmidt, Tupman (1870), and
others; but it was not known until my observations in 1878 that the
Aquarids formed the special display of the epoch, and that there were
many early Perseids visible at the same time.
_Perseids._ Muschenbroeck, in his work on ‘Natural Philosophy,’ printed
in 1762, mentions that he observed shooting-stars to be more numerous
in August than in the other months of the year. Quetelet, in 1835, was,
however, the first to attribute a definite maximum to the 9th-10th.
This stream is remarkable for its extended duration, and for the
obvious displacement which occurs from night to night in the place of
its radiant. It furnishes an annual display of considerable strength,
and is, perhaps, the best known system of all.
_Orionids._ Profs. Schmidt and Herschel were the first to discover
the Orionids as the most brilliant display of the October period, and
accurately determined its radiant in 1863-4-5. Herrick recorded a
shower at 99° +26°, Oct. 20-26, 1839, and Zezioli in 1868 recorded many
meteors which were ascribed to a radiant at 111° +29°; but there is no
doubt that the Orionids were observed in both these cases, though the
radiant was badly assigned.
The radiant of the Orionids shows no displacement like that of the
Perseids.
_Leonids._ Observed from the earliest times. Humboldt and Bonpland saw
it well on the night of November 11-12, 1799, and the phenomenon at its
magnificent return on November 12, 1833, was ably discussed by Olmsted.
It furnished a splendid shower in 1866, November 13, and many meteors
were seen at the few subsequent returns. I observed fairly conspicuous
showers of Leonids in 1879 and 1888. There is no doubt the meteors form
a complete ellipse, for the earth encounters a few of them at every
passage through the node. Grand displays may be expected at the end of
this century.
_Andromedes._ Observed by Brandes, at Hamburg, Dec. 7, 1798. It also
recurred in 1838; the very brilliant showers of November 27, 1872 and
1885, are still fresh in the memory. It is uncertain whether this group
forms an unbroken stream; if so, the regions far removed from the
parent comet must be extremely attenuated. Some of the meteors were
seen in 1877 and 1879. The radiant is diffuse to the extent of 7° or
10°. Returns of the shower should be looked for in 1892 and 1898.
_Geminids._ Mr. Greg first called attention to the importance of this
shower. It was well observed by Prof. Herschel in 1861-3-4, and some
later years.
There are an enormous number of minor systems, but these are generally
feeble, and interesting only to the regular observer of meteors. Many
showers are so slightly manifested that they yield but one visible
meteor in 6 or 7 hours, and on the same night of observation there are
often as many as 50 or 60 different systems in operation. I gave a list
of 918 radiant-points of showers observed at Bristol in the ‘Monthly
Notices,’ May 1890, and other catalogues will be found in the ‘British
Association Reports’ for 1874 and 1878.
_Varieties of Meteors._—The amateur who systematically watches for
meteors will occasionally remark instances of anomalous character.
I have sometimes observed meteors which are apparently very near,
and move with enormous velocity. They are mere gleams of pale light,
which have little analogy to ordinary shooting-stars, and suggest an
electric origin, though I do not know whether the marvellous quickness
with which they flash upon the eye is not to be held responsible for
the impression of nearness. They are somewhat rare, and one may watch
through several entire nights without a single example, but as far as
my memory serves I must have witnessed some scores of these meteoric
flashes.
One of the most interesting class of meteors includes those which
move so slowly that the eye is enabled to note the details of their
appearance. Some of these objects are small when first seen, but
enlarge considerably under the increasing temperature, and after a
great slackening of speed (due to atmospheric resistance) their nuclei
are finally spent in thick streams of luminous dust. On Dec. 28, 1888,
I recorded a meteor which on its first apparition was tolerably bright,
small, and compact. It moved slowly, and I had an excellent view of
its passage. The nucleus quickly expanded, though with no increase of
brilliancy. Towards the end it assumed a sensible disk, and at the
last phase the mass spread or deployed itself into a wide stream of
fine ashes and disappeared. The whole phenomenon was so curious, and
observed with such distinctness, that I made the above sketch of it
directly afterwards.
[Illustration: Fig. 58.
Meteor of Dec. 28, 1888, 6^h 17^m.]
_Heights of Meteors._—Usually the height of meteors at their first
appearance is less than 90 miles, and at disappearance more than 40
miles. From a comparison of a large number of computations I derived
the following average values:—
Beginning height 76·4 miles (683 meteors)
End height 50·8 ” (756 ” )
But if fireballs and the smaller shooting-stars are separated I
find the usual heights at disappearance are:—fireballs, 30 miles;
shooting-stars, 54 miles. Fireballs therefore approach much nearer to
the Earth’s surface before disruption than the ordinary falling stars.
[Illustration: Fig. 59.
Large Meteor, and successive appearances of its streak, seen at Cape
Jask, in the Persian Gulf, on June 8, 1883, 7^h 51^m to 8^h 33^m.]
A very slight acquaintance with trigonometry will enable anyone to
compute the real path of a meteor if two or more observations, made at
distant stations, are available for the purpose. The observed courses
of the meteor should be marked upon a celestial globe, and extended
backwards to the point where they mutually intersect; this will be the
_radiant-point_. The globe having been set for the time and latitude,
the apparent tracks should also be prolonged in a forward direction
until they meet the horizon, this will indicate the _Earth-points_, or
azimuths of the place where the meteor would have been precipitated
on the Earth had it been enabled to continue its flight so far. The
azimuths and altitudes of the beginning and end of the path, and the
azimuths of the Earth-point should then be read off, and by means of
a reliable map and a protractor their points of intersection over the
Earth’s surface may be readily found by lines drawn from the two
places of observation. From the spot where the Earth-points intersect a
straight line should also be drawn in the direction of the radiant, and
it is along this line the meteor’s motion was directed. The coordinates
of the observed points of appearance and disappearance of the meteor,
at the two stations, would intersect this line at identical points were
the observations perfectly accurate, but this is rarely the case. The
distance between the observer’s station and the places over which the
meteor began and ended is easily derived from the map, and the height
of the object may be found by adding the logarithm of the distance to
the log. of the tangent of the altitude. Thus, if the end of a meteor
is witnessed from London in azimuth 130° W. of S. (alt. 25°), and from
Bristol in azimuth 216° W. of S. (alt. 30°) the place of intersection
on the map will be at Warwick, so that the meteor must have disappeared
when vertically over this city. London is distant from Warwick about
86 miles, and from Bristol 70 miles, and the resulting height of the
meteor is:—
London. Bristol.
86 log. 1·93450 70 log. 1·84510
25° tan 9·66867 30° tan 9·76144
———- ———-
1·60317 = 40·1 1·60654 = 40·4
so that the observations accord very closely in fixing the height at a
little exceeding 40 miles at disappearance, but a slight correction is
necessary to allow for the Earth’s curvature. There are other methods
of computing the heights, one of which is explained by Prof. A. S.
Herschel in a paper entitled “Height of a Meteor” (‘Monthly Notices,’
vol. xxv. p. 251).
_Meteoric Observations._—A large number of meteor-showers still await
discovery, and there are features even in connection with the best
known streams which remain to be elucidated. Such doubts as now exist
are only to be cleared away by assiduous observation made with the
utmost accuracy possible both of the _directions_ and _durations_ of
meteors.
This attractive field of investigation has certainly been neglected
in recent years, and the reason of this may perhaps be found in the
complications inseparable from it, in the need of great patience
and scrupulous care in observation, and the necessity of gaining
experience before the observer can feel a reliance on his work,
and draw safe conclusions. Meteors are so fugitive, so diverse and
erratic in their apparitions, as to be quite beyond the scope of
instrumental refinements. They must necessarily be observed under many
disadvantages. Positions have to be fixed from very hurried and often
imperfect impressions. But these drawbacks, formidable as they at
first appear, may be severally overcome by practice, by careful regard
for the conditions under which meteors are displayed, and the marked
differences of aspect induced by these conditions. When the observer
has acquired a practical knowledge he will proceed with confidence in
his work, and avoid many of the difficulties surrounding it.
In recording meteor-tracks for the purpose of discovering the
radiant-points, the chief feature in which precision is essential is
the _direction_ of flight. A perfectly straight wand, held in the hand
for the purpose, should be projected upon the path of every meteor
directly it is seen, and then when the eye has quickly noted the
position and slope relatively to the fixed stars near, it should be
reproduced on the chart or celestial globe. The time, mag., estimated
duration, and details of appearance should be registered in a tabular
form, with the R.A. and Dec. of the beginning-point and probable
radiant. The end-point and length of path may be left until next day,
in order to save valuable time. The wand is a great assistance to the
eye in retaining the approximate directions and noting the places.
If a meteor belongs to the slow, trained class, or if it belongs to
the swift, streak-leaving order, the path may be very accurately
noted, for the wand can be adjusted to its direction before the meteor
or its visible offcome has died away. In the case of short, quick
meteors, devoid of either streaks or trains, and generally shooting
from radiants at high altitudes, they are more difficult to secure, as
they vanish before one may turn, and the observer must rely upon the
mere impression he received. But even these succumb to experience, and
will be found to resolve themselves into a number of sharply defined
radiants scarcely less certain than the positions derived from the
streaked or trained meteors.
These positions are only to be fixed by the exercise of much cautious
discrimination on the part of the observer, for the direction of the
flight is not sufficient, alone, to indicate it. The visible aspect of
the meteor has to be equally considered, for the place of its radiant
imparts certain peculiarities to it which are rarely to be mistaken.
First, _the astronomical position_ of the radiant. If the radiant is
at, or within 50° of, the Earth’s apex (a point 90° preceding the Sun
along the ecliptic, and towards which the Earth’s motion is directed)
the meteors generally leave streaks, especially the brighter ones, and
move with great speed. They are usually white, exhibiting a high degree
of incandescence. If the radiant is near the anti-apex or anywhere
in the anti-apex half-sphere the meteors are streakless, they travel
slowly or very slowly, and often leave trails of yellowish sparks.
Bearing these facts in mind the region may be assigned in which any
radiant is situated, if not the exact position of the radiant itself.
If, say, on Aug. 10, at midnight a swift, streaked meteor is seen
shooting from the Pleiades towards Aldebaran, just risen, the radiant
is either in Musca, Triangulum, or Andromeda. But if the meteor is
slow, with a train, then we must go further back in the direction of
its flight, and seek the radiant in the S. or S.W. sky. If the motion
is very slow, the radiant may be as far away as Aquila. Second, _the
sensible position of the radiant_. A low radiant yields long-pathed
meteors, characterized by slowness of speed and a flaky appearance
either of the streaks or trains. A radiant near the zenith gives
short, darting meteors, with rather dense streaks or trains. These
nearly vertical meteors have a less extensive range of atmosphere to
penetrate than the horizontal meteors, which are sometimes abnormally
long. In the case of brilliant meteors, however, the paths occasionally
extend over considerable arcs though the radiant may be high. Third,
_the position of the radiant relatively to the path of a meteor_. If a
meteor is close to its radiant its track is usually slow, and appears
greatly foreshortened by the effects of perspective. It is travelling
(approaching) nearly in the line of sight, and the streak or offcome
of sparks is especially dense because it is seen through its entire
depth; and the nucleus in such a case has a brushy diffused appearance.
Such meteors often traverse sinuous, or curved paths of 2°, 3°, or 4°,
and they are readily distinguishable from other meteors far from the
radiants to which they belong.
A good method of tabulating meteor-tracks is that adopted by
Lieut.-Col. Tupman in his catalogue published by the British
Association in 1874. I have adopted the same form, and herewith append
a copy of my register of a few isolated bright meteors observed in the
autumn of 1890:—
+————————+——————+——————+————————————————————-+——————+————-+
| | | | Observed Path | | |
| Date |G.M.T.| Mag. +————————-+——————————-+Length|Dura-|
| 1890. | | | From | To | of |tion.|
| | | |R.A. Dec.| R.A. Dec | Path.| |
+————————+——————+——————+————————————————————-+——————+————-+
| | h m| | o o | o o | o | sec.|
|Oct+. 17| 10 37| >1 | 219+61 | 255+65 | 16 | 3·5 |
| 19| 10 35| 1 | 61½+26 | 44½+27½ | 15½ | 0·7 |
| 19| 12 0| ½ ☽ | 326-8 | 319-10 | 7 | 0·5 |
| 25| 17 18| >♃ | 168+34 | 180+24 | 14½ | 0·8 |
| 26| 7 33| ♃ | 329+69 | 243+51 | 42 | 4·0 |
|Nov. 1 | 7 1| >1 | 278+49 | 244+11½ | 46 | 6·0 |
| 1 | 9 17| >1 | 345+11 | 307+1½ | 39 | 4·0 |
| 5 | 10 40| >♀ | 28½-25 | 25½-29½ | 5½ | 0·7 |
| 16 | 11 15| ♃ | 274+77 | 265½+67 | 10 | 1·5 |
+————————+——————+——————+————————————————————-+——————+————-+
+————————+—————————————————————+————————+
| | | |
| Date | Appearance. |Probable|
| 1890. | |Radiant.|
| | | |
+————————+—————————————————————+————————+
| | | o o |
|Oct+. 17| V. slow, B. train. | 204+56.|
| 19| Swift, streak. | Orion. |
| 19| Swift, streak. | Orion. |
| 25 |Swift, streak. | Lynx. |
| 26| Slow. | 32+18. |
|Nov. 1 | Very slow. | 50+15. |
| 1 | Slow. | 50+15. |
| 5 | Swift, strk. 15 sec.| Taurus.|
| 16 | Not very swift. | Auriga.|
+————————+—————————————————————+————————+
The _duration of flight_ is a most important element to estimate
correctly, as it affords data wherewith the real velocity may be
computed, and enables the nature of the orbit in which the meteor is
moving to be definitely assigned. This feature is, however, one of the
most difficult of all to derive with satisfactory precision. In the
case of very slow meteors lasting several seconds, it is easy by means
of a stop-watch, or by other methods, to get the times of flight within
narrow limits of error, but the swifter class of meteors complete their
visible trajectories in the fraction of a second, and are gone before
any effort can be made to gauge their durations, so that a value has to
be attributed which is little better than a mere guess.
Every adopted radiant-point should be based on at least five paths,
unless the conditions are special, and these must show a very definite
centre, and present family resemblances. It is often possible to detect
a good centre from very few paths, when the radiant is low on the
horizon, or when it occupies an isolated position.
In recording meteors the details of their appearances should also be
appended to the paths. Foreshortened and crooked courses, fluctuations
of brightness, halting motion, spark-trains, phosphorescent streaks,
broken streaks, and other features must be invariably noted when
observed, as likely to assist in fully comprehending these bodies. A
streak will sometimes brighten up perceptibly after the head has died
out.
One of the principal aims of future observers should be to ascertain
the visible duration of meteor-showers, and the displacement or fixed
position of the radiants during the period of their continuance. The
Perseids seem to endure for forty-six nights (July 8-August 22) while
the radiant moves from 3° +49° to 76° +57°. The Lyrids also exhibit
a shifting radiant, and it is highly probable some other showers are
to be included in the same category. In investigating these, the
observations of single nights should be kept separate, and the radiant
determined from each set of paths. The positions when compared will
then exhibit the rate and direction of the displacement. As to radiants
which are apparently stationary[46] during long intervals, these should
be closely observed. Are the centres of radiation, as successively
determined, identical, allowing for the slight errors of observation?
Are they continuously in operation, or intermittent? Meteors with
motions in declination and near their radiants will be specially
valuable in settling these questions, and if observed at more than one
station will possess great significance. If it can be proved that a
radiant is fixed and continuous during a few weeks, there can be no
reason why it may not be stationary for a much more lengthy interval,
unless the circumstances are exceptional.
Though I have pointed out the urgency of noting the directions and
durations of meteors, there are other features in such observations
that must not be disregarded. If the paths are being recorded for the
particular purpose of getting duplicate observations and calculating
the heights, then it is desirable to note the beginning-and end-points
of the flights as exactly as possible, for unless this is done the
combined paths will show great discordances. Those who have acquired
a familiar knowledge of the constellations will, however, experience
little trouble in insuring accuracy in these records.
Observers, particularly those residing in towns, must be constantly on
their guard against mistakes in identifying meteors from terrestrial
objects such as fire-balloons and the various forms of pyrotechnic
display. That such caution is necessary will be admitted when we read
the two following letters, which were published in the ‘Times’ some
years ago:—
“SIR,—
“A large meteor was seen to-night at 8.27, moving very slowly along
the northern horizon, from west to east, at an altitude of about 8
deg. It was at least three times as brilliant as Venus, remaining
visible for nearly five minutes, moving slower than any hitherto
observed. I should be glad to receive observations made at more
favourable stations....
“I remain, Sir, your obedient Servant,
“THOMAS CRUMPLEN.
“Mr. Slater’s Observatory, Euston Road, August 10th.”
“SIR,—
“The ‘large meteor’ seen by Mr. Crumplen on Monday evening at 8.27,
three times as brilliant as Venus, and moving from west to east,
was a fire-balloon sent up shortly after 8 o’clock from the Eton
and Middlesex Cricket Ground, Primrose Hill, as a _finale_ to some
athletic sports which had taken place during the afternoon.
“I am, Sir, your obedient Servant,
“B. C. C.
“St. John’s Wood, August 12th.”
In concluding this chapter I may briefly mention that an old idea
concerning meteors was that they originated gales of wind, and that, in
fact, they were the usual precursors of stormy weather. This belief is
thus expressed in Dryden’s ‘Virgil’:—
“Oft shalt thou see, ere brooding storms arise,
Star after star glide headlong down the skies,
And, where they shot, long trails of lingering light,
Sweep far behind, and gild the shades of night.”
FOOTNOTES:
[45] During the seven months from May to November 1890 I noted
ninety-five telescopic meteors while engaged in comet-seeking.
[46] A list of these was published in the ‘Monthly Notices,’ vol. 1. p.
466. See also ‘Monthly Notices,’ vol. xlv. pp. 93 _et seq._