PHENOMENA OF METEORS, OPTIC DELUSIONS, SPECTRA, ETC.
The meteors known to the ancients were called [Greek: Lampdes Pithoi]
Bolides, Faces, Globi, etc. from particular differences in their shape
and appearance, and sometimes under the general term of comets. In the
Philosophical Transactions, they are called, indiscriminately,
fire-balls, or fiery meteors; and names of similar import have been
applied to them in the different languages of Europe. The most material
circumstances observed of such meteors may be brought under the
following heads: 1. Their general appearance. 2. Their path. 3. Their
shape or figure. 4. Their light and colour. 5. Their height. 6. The
noise with which they are accompanied. 7. Their fire. 8. Duration, 9.
Their velocity. Under these different heads meteors have been
investigated by the scrutinizing of philosophy, and many superstitious
notions, long entertained concerning them, entirely exploded. Meteoric
phenomena, it has been demonstrated, all proceed from one common
cause--irregularity in the density of the atmosphere. When the
atmospheric fluid is homogenous and of equal density, the rays of light
pass without obstruction or alteration in their shape or direction; but
when they enter from a rarer into a denser medium, they are refracted or
bent out of their course; and this with greater or less effect according
to the different degrees of density in the media, or the deviation of
the ray from the perpendicular. If the second medium be very dense in
proportion, the ray will be both refracted and reflected; and the object
from which it proceeds, will assume a variety of grotesque and
extraordinary shapes, and it will sometimes appear as in a reflection
from a concave mirror, dilated in size, and changed in situation.
The following striking effects are known to proceed from this simple
cause.
The first is the mirage, seen in the desert of Africa. M. Monge, a
member of the National Institute, accompanied the French army into
Egypt. In the desert, between Alexandria and Cairo, the mirage of the
blue sky was inverted, and so mingled with the sand below, as to impart
to the desolate and arid wilderness an appearance of the most rich and
beautiful country. They saw, in all directions, green islands,
surrounded with extensive lakes of pure and transparent water. Nothing
could be conceived more lovely and picturesque than this landscape. On
the tranquil surface of the lakes, the trees and houses, with which the
islands were covered, were strongly reflected with vivid hues, and the
party hastened forward to enjoy the cool refreshments of shade and
stream, which these populous villages preferred to them. When they
arrived, the lake, on whose bosom they floated, the trees, among whose
foliage they were embowered, and the people who stood on the shore
inviting their approach, had all vanished, and nothing remained but an
uniform and irksome desert of sand and sky, with a few naked huts and
ragged shrubs. Had they not been undeceived by their nearer approach,
there was not a man in the French army who would not have sworn, that
the visionary trees and lakes had a real existence in the midst of the
desert.
The same appearance precisely was observed by Dr. Clarke at Raschid, or
Rosetta. The city seemed surrounded by a beautiful sheet of water, and
so certain was his Greek interpreter, who was acquainted with the
country, of this fact, that he was quite indignant at an Arab, who
attempted to explain to him, that it was a mere optical delusion. At
length, they reached Rosetta in about two hours, without meeting any
water; and, on looking back on the sand they had just crossed, it seemed
to them, as if they had just waded through a vast blue lake.
A similar deception takes place in northern climates. Cities,
battlements, houses, and all the accompaniments of populous places, are
seen in desolate regions, where life goes out, and where human foot has
never trod. When approached they vanish, and nothing remains but a
rugged rock, or a misshapen iceberg.
Captain Scoresby, in his voyage to the arctic regions, on the coast of
East Greenland, constantly saw those visionary cities, and gives some
highly curious plates of the appearances they presented. They resembled
the real cities seen on the coast of Holland, where towers, and
battlements, and spires, "bosomed high in tufted trees," rise on the
level horizon, and are seen floating on the surface of the sea. Among
the optic deceptions noticed by Captain Scoresby, was one of a very
singular nature. His ship had been separated by the ice, from that of
his father for some time; and he was looking for her every day, with
great anxiety. At length, one evening, to his utter astonishment, he saw
her suspended in the air in an inverted position, traced on the horizon
in the clearest colours, and with the most distinct and perfect
representation. He sailed in the direction in which he saw this
visionary phenomenon, and actually found his father's vessel by its
indication. He was divided from him by immense masses of icebergs, and
at such a distance that it was quite impossible to have seen the ship in
her actual situation, or seen her at all, if her spectrum, or image, had
not been thus raised several degrees above the horizon into the sky, by
this most extraordinary refraction, in the same manner as the sun is
often seen, after he is known to have set, and actually sunk far below
the line of direct vision.
The _Fata Morgana_ are further illustrations of this optic delusion.
This phenomenon is seen at the Pharo of Messina, in Sicily, under
certain circumstances. The spectator must stand with his back to the
east, on an elevated place behind the city, commanding a view of the
bay, and having the mountains, like a wall, opposite to him, to darken
the back ground of the picture; no wind must be abroad to ruffle the
surface of the sea; and the waters must be pressed up by currents, as
they sometimes are, to a considerable height in the middle of the
strait, and present a slight convex surface. When all these
circumstances occur, as soon as the sun rises over the heights of the
Calabrian shore, and makes an angle of 45º with the horizon, all the
objects on the shore at Reggio are transferred to the middle of the
strait, and seen distinctly on the surface of the water, forming an
immoveable landscape of rocks, trees, and houses, and a moveable one of
men, horses, and cattle; these are formed into a thousand separate
compartments, presenting most beautiful and ever varying pictures of
animate and inanimate nature, on the swelling surface of the water,
broken by the currents, present separate plates of convex mirrors to
reflect them; they then as suddenly disappear, as the broad aquatic
mirror of the current passes on.
Sometimes the atmosphere is so dense that the objects are seen, like
Captain Scoresby's ship, snatched up into the regions of the air, thirty
or forty feet above the level of the sea; and in cloudy weather, nearer
to the surface, bordered with vivid prismatic colours. Sometimes
colonades of temples and churches, with cross-crowned spires, are all
represented as floating on the sea, and by a sudden change of
representation, the pillars are curved into arcades, and the crosses are
bent into crescents, and all the edifices of the floating city undergo
the most extraordinary and fantastic mutations. All these images are so
distinct, and produce objects seemingly as palpable as they are visible,
as sensible to touch as to sight, that the people of the country are
firmly persuaded of their reality. They consider the edifices as the
enchanted palaces of the fairy Morgana, and the moving objects as living
things which inhabit them. Whenever the optic phenomenon occurs, they
meet together in crowds, with an intense curiosity, mixed with awe and
apprehension, which is not removed by an acquaintance with those natural
causes, by which Mr. Swinburn and other foreign travellers, who have
witnessed the scene, are able to account for it.
The lakes of Ireland are equally susceptible of producing those vivid
delusions, and the imagination of the people, as lively as that of the
Sicilians, clothes them with an equal reality. There is scarcely a loch
in that country, in which the remains of cities have not been at various
times discovered; and many men have been met with who would solemnly
swear they saw, and who no doubt did see, representations of them in
certain states of the atmosphere. The most celebrated is that which
occurs on the lake of Killarney. This romantic sheet of water is bounded
on one side by a semi-circle of rugged mountains, and on the other by a
flat morass, and the vapour generated in the mass, and broken by the
mountains, continually represent the most fantastic objects; and often
those on shore are transferred to the water, like the Fata Morgana.
Many of the rocks are distinguished for their marked and lengthened
echoes, and the structure, which in acoustics reflects sounds to the
ear, from a point from whence they did not come, reflects images on the
eye, from a place very different from where the objects stood which
produced them. Frequently men riding along shore, are seen as if they
were moving across the lake, and this has given rise to the story of
O'Donougho. This celebrated chieftain was, according to the tradition of
the country, endued with the gift of magic; and, on one occasion, his
lady requested him to change his shape, that she might see a proof of
it. He complied, on condition that she would not be terrified, as such
an effect on her must prove fatal to him. Her mind failed her, however,
in the experiment, and at the sight of some horrible figure he assumed,
she shrieked, and he disappeared through the window of his castle, which
overhung the lake. From that time he continues an enchanted being,
condemned to ride a horse, shod with silver, over the surface of the
lake, till his horse's shoes are worn out. On every May morning he is
visible, and crowds assemble on the shore to see him. Many affirm they
have seen him; and one person relates many particulars of his
apparition, that the deception must have proceeded from some real
object, a man riding along shore, and transferred to the middle of the
water, by the optic delusion of the Fata Morgana.
But perhaps the most wonderful, and apparently preternatural effect
arising from this cause, is the _spectre of the Hartz Mountains_ in
Hanover. There is one particular hill, called the Brocken, in which he
appears, terrifying the credulous, and gratifying the curious to a very
high degree. The most distinct and interesting account is given by Mr.
Hawe, who himself was a witness to it. He had climbed to the top of the
mountain thirty times, and had been disappointed, but he persevered, and
was at length highly gratified. The sun rose about four o'clock in a
serene sky, free from clouds, and its rays passed without obstruction,
over another mountain, called the Heinschoe. About a quarter past five
he looked round to see if the sky was clear, and if there was any chance
of his witnessing what he so ardently wished, when suddenly he saw the
Achtermanshoe, a human figure of monstrous size turned towards him, and
glaring at him. While gazing on this gigantic spectre with wonder mixed
with an irrepressible feeling of awe and apprehension, a sudden gust of
wind nearly carried off his own hat, and he clapped his hand to his head
to detain it, when to his great delight the colossal spectre did the
same. He then changed his body into a variety of attitudes, all which
the figure exactly imitated, but at length suddenly vanished without any
apparent cause, and again as suddenly appeared. He called the landlord
of the inn, who had accompanied him, to stand beside him, and in a
little time two correspondent figures, of dilated size, appeared on the
opposite mountain. They saluted them in various ways by different
movements of their bodies, all which the giants returned with perfect
politeness, and then vanished. A traveller now joined Mr. Hawe and the
innkeeper, and they kept steadily looking for their aerial friends, when
they suddenly appeared again three in number, who all performed exactly
the same movements as their correspondent spectators. Having continued
thus for some time, appearing and disappearing alternately, sometimes
faintly, and sometimes more distinct, they at length faded away not
again to return. They proved, however, that the preternatural spectre,
which had so long filled the country with awe and terror, was no unreal
being, still less an existence whose appearance suspended the ordinary
laws of God and Nature; that, on the contrary, it was the simple
production of a common cause, exhibited in an unusual manner, but as
regular an effect, and as easy to be accounted for, as the reflection of
a face in a looking glass.
This constitution of the atmosphere, and its capability of dilating
objects, and altering their position by reflection and refraction, will
easily account for many phenomena which have been considered miraculous
and preternatural in early ages, by the ignorant; and in our own, by the
weak and superstitious. Such was probably the origin of the crosses seen
by Constantine and Constantius in the first ages of Christianity, and
such was that of the cross which appeared in the sky in France, to which
so many bore attestation. A large cross of wood, painted red, had been
erected beside the church, as a part of the ceremony they were
performing. In the winter, when the air is most frequently condensed by
cold, and its different strata of various degrees of tenacity, on a
clear evening after rain, when particles of humidity, still floating in
the air gives it greater power of reflection and refraction, when the
sun was setting, and his horizontal beams found most favourable to
produce meteoric phenomena, the spectrum of this wooden cross was cast
on the concave surface of some atmospheric mirror, and so reflected
back to the eyes of the spectators from an opposite place, retaining
exactly the same shape and proportions, but dilated in size, and changed
in position; and it was moreover tinged with red, the very colour of the
object of which it was the reflected image. This delusive appearance
continued till the sun was so far sunk below the horizon, as to afford
no more light to illumine the object, and the image ceased when the rays
were no longer distinctly reflected.