Natural phenomena marked with the marvellous--Spectre of the
Brocken described--Analogous phenomena--Aërial spectres seen in
Cumberland--Fata Morgana in the Straits of Messina--Objects below the
horizon raised and magnified by refraction--Singular example seen at
Hastings--Dover Castle seen through the hill on which it stands--Erect
and inverted images of distant ships seen in the air--Similar
phenomena seen in the Arctic regions--Enchanted coast--Mr.
Scoresby recognizes his father’s ship by its aërial image--Images
of cows seen in the air--Inverted image of horses seen in South
America--Lateral images produced by refraction--Aërial spectres by
reflexion--Explanation of the preceding phenomena.
Among the wonders of the natural world which are every day presented
to us, without either exciting our surprise or attracting our notice,
some are occasionally displayed which possess all the characters of
supernatural phenomena. In the names by which they are familiarly
known, we recognize the terror which they inspired, and even now,
when science has reduced them to the level of natural phenomena, and
developed the causes from which they arise, they still retain their
primitive importance, and are watched by the philosopher with as
intense an interest as when they were deemed the immediate effects
of Divine power. Among these phenomena we may enumerate the _Spectre
of the Brocken_, the _Fata Morgana_ of the Straits of Messina, the
_Spectre Ships_ which appear in the air, and the other extraordinary
effects of the _Mirage_.[14]
[14] In the Sanscrit, says Baron Humboldt, the phenomenon of the
Mirage is called _Mriga Trichna_, “thirst or desire of the antelope,”
no doubt because this animal _Mriga_, compelled by thirst, _Trichna_,
approaches those barren plains where, from the effect of unequal
refraction, he thinks he perceives the undulating surface of the
waters.--_Personal Narrative_, vol. iii., p. 554.
The Brocken is the name of the loftiest of the Hartz mountains, a
picturesque range which lies in the kingdom of Hanover. It is elevated
3,300 feet above the sea, and commands the view of a plain seventy
leagues in extent, occupying nearly the two-hundredth part of the
whole of Europe, and animated with a population of above five millions
of inhabitants. From the earliest periods of authentic history, the
Brocken has been the seat of the marvellous. On its summits are still
seen huge blocks of granite called the Sorcerer’s Chair and the Altar.
A spring of pure water is known by the name of the Magic Fountain,
and the Anemone of the Brocken is distinguished by the title of the
Sorcerer’s Flower. These names are supposed to have originated in the
rites of the great idol Cortho, whom the Saxons worshipped in secret
on the summit of the Brocken, when Christianity was extending her
benignant sway over the subjacent plains.
As the locality of these idolatrous rites, the Brocken must have been
much frequented, and we can scarcely doubt that the spectre which now
so often haunts it at sunrise must have been observed from the earliest
times; but it is nowhere mentioned that this phenomenon was in any
way associated with the objects of their idolatrous worship. One of
the best accounts of the spectre of the Brocken is that which is given
by M. Haue, who saw it on the 23rd of May, 1797. After having been on
the summit of the mountain no less than thirty times, he had at last
the good fortune of witnessing the object of his curiosity. The sun
rose about four o’clock in the morning through a serene atmosphere.
In the south-west, towards Achtermannshohe, a brisk west wind carried
before it the transparent vapours, which had not yet been condensed
into thick heavy clouds. About a quarter past four he went towards the
inn, and looked round to see whether the atmosphere would afford him a
free prospect towards the south-west, when he observed at a very great
distance, towards Achtermannshohe, a human figure of a monstrous size.
His hat having been almost carried away by a violent gust of wind,
he suddenly raised his hand to his head to protect his hat, and the
colossal figure did the same. He immediately made another movement by
bending his body,--an action which was repeated by the spectral figure.
M. Haue was desirous of making further experiments, but the figure
disappeared. He remained, however, in the same position, expecting
its return, and in a few minutes it again made its appearance on the
Achtermannshohe, when it mimicked his gestures as before. He then
called the landlord of the inn, and having both taken the same position
which he had before, they looked towards the Achtermannshohe, but saw
nothing. In a very short space of time, however, two colossal figures
were formed over the above eminence, and after bending their bodies
and imitating the gestures of the two spectators, they disappeared.
Retaining their position, and keeping their eyes still fixed upon the
same spot, the two gigantic spectres again stood before them, _and were
joined by a third_. Every movement that they made was imitated by the
three figures, but the effect varied in its intensity, being sometimes
weak and faint, and at other times strong and well defined.
[Illustration: _Fig. 30._]
In the year 1798, M. Jordan saw the same phenomenon at sunrise, and
under similar circumstances, but with less distinctness, and without
any duplication of the figures.[15]
[15] See J. F. Gmelin’s _Gottingischen Journal der Wissenchaften_,
vol. i., part iii., 1798.
Phenomena perfectly analogous to the preceding, though seen under less
imposing circumstances, have been often witnessed. When the spectator
sees his own shadow opposite to the sun upon a mass of thin fleecy
vapour passing near him, it not only imitates all his movements, but
its head is distinctly encircled with a halo of light. The aërial
figure is often not larger than life, its size and its apparent
distance depending, as we shall afterwards see, upon particular causes.
I have often seen a similar shadow when bathing in a bright summer’s
day in an extensive pool of deep water. When the fine mud deposited
at the bottom of the pool is disturbed by the feet of the bather, so
as to be disseminated through the mass of water in the direction of
his shadow, his shadow is no longer a shapeless mass formed upon the
bottom, but is a regular figure formed upon the floating particles of
mud, and having the head surrounded with a halo, not only luminous, but
consisting of distinct radiations.
One of the most interesting accounts of aërial spectres with which we
are acquainted has been given by Mr. James Clarke, in his Survey of the
Lakes of Cumberland, and the accuracy of this account was confirmed by
the attestations of two of the persons by whom the phenomena were first
seen. On a summer’s evening, in the year 1743, when Daniel Stricket,
servant to John Wren, of Wilton Hall, was sitting at the door along
with his master, they saw the figure of a man with a dog pursuing some
horses along Souterfell-side, a place so extremely steep, that a horse
could scarcely travel upon it at all. The figures appeared to run at
an amazing pace, till they got out of sight at the lower end of the
Fell. On the following morning, Stricket and his master ascended the
steep side of the mountain, in the full expectation of finding the man
dead, and of picking up some of the shoes of the horses, which they
thought must have been cast while galloping at such a furious rate.
Their expectations, however, were disappointed. No traces, either of
man or horse, could be found, and they could not even discover upon the
turf the single mark of a horse’s hoof. These strange appearances seen
at the same time by two different persons in perfect health, could not
fail to make a deep impression on their minds. They at first concealed
what they had seen, but they at length disclosed it, and were laughed
at for their credulity.
In the following year, on the 23rd June, 1744, Daniel Stricket, who
was then servant to Mr. Lancaster, of Blakehills, (a place near
Wilton Hall, and both of which places are only about half a mile
from Souterfell,) was walking, about seven o’clock in the evening,
a little above the house, when he saw a troop of horsemen riding
on Souterfell-side, in pretty close ranks, and at a brisk pace.
Recollecting the ridicule that had been cast upon him the preceding
year, he continued to observe the figures for some time in silence;
but being at last convinced that there could be no deception in the
matter, he went to the house, and informed his master that he had
something curious to show him. They accordingly went out together; but
before Stricket had pointed out the place, Mr. Lancaster’s son had
discovered the aërial figures. The family was then summoned to the
spot, and the phenomena were seen alike by them all. The equestrian
figures seemed to come from the lowest parts of Souterfell, and became
visible at a place called Knott. They then advanced in regular troops
along the side of the Fell, till they came opposite to Blakehills, when
they went over the mountain, after describing a kind of curvilineal
path. The pace at which the figures moved was a regular swift walk,
and they continued to be seen for upwards of two hours, the approach
of darkness alone preventing them from being visible. Many troops
were seen in succession; and frequently the last but one in a troop
quitted his position, galloped to the front, and took up the same pace
with the rest. The changes in the figures were seen equally by all
the spectators, and the view of them was not confined to the farm of
Blakehills only, but they were seen by every person at every cottage
within the distance of a mile, the number of persons who saw them
amounting to about twenty-six. The attestation of these facts, signed
by Lancaster and Stricket, bears the date of the 21st July, 1785.
These extraordinary sights were received not only with distrust, but
with absolute incredulity. They were not even honoured with a place in
the records of natural phenomena, and the philosophers of the day were
neither in possession of analogous facts, nor were they acquainted with
those principles of atmospherical refraction upon which they depend.
The strange phenomena, indeed, of the _Fata Morgana_, or the _Castles
of the Fairy Morgana_, had been long before observed, and had been
described by Kircher in the 17th century, but they presented nothing
so mysterious as the aërial troopers of Souterfell; and the general
characters of the two phenomena were so unlike, that even a philosopher
might have been excused for ascribing them to different causes.
This singular exhibition has been frequently seen in the straits of
Messina, between Sicily and the coast of Italy, and whenever it takes
place, the people, in a state of exultation, as if it were not only
a pleasing but a lucky phenomenon, hurry down to the sea, exclaiming
_Morgana, Morgana!_ When the rays of the rising sun form an angle
of 45° on the sea of Reggio, and when the surface of the water is
perfectly unruffled, either by the wind or the current, a spectator
placed upon an eminence in the city, and having his back to the sun
and his face to the sea, observes upon the surface of the water superb
palaces, with their balconies and windows, lofty towers, herds and
flocks grazing in wooded valleys and fertile plains; armies of men
on horseback and on foot, with multiplied fragments of buildings,
such as columns, pilasters, and arches. These objects pass rapidly in
succession along the surface of the sea during the brief period of
their appearance. The various objects thus enumerated are pictures
of palaces and buildings actually existing on shore, and the living
objects are of course only seen when they happen to form a part of the
general landscape.
If, at the time that these phenomena are visible, the atmosphere is
charged with vapour or dense exhalations, the same objects which are
depicted upon the sea will be seen also in the air, occupying a space
which extends from the surface to the height of twenty-five feet. These
images, however, are less distinctly delineated than the former.
If the air is in such a state as to deposit dew, and is capable of
forming the rainbow, the objects will be seen only on the surface of
the sea; but they all appear fringed with red, yellow, and blue light,
as if they were seen through a prism.
In our own country, and in our own times, facts still more
extraordinary have been witnessed. From Hastings, on the coast of
Sussex, the cliffs on the French coast are fifty miles distant,
and they are actually hid by the convexity of the earth; that is,
a straight line drawn from Hastings to the French coast would pass
through the sea. On Wednesday, the 26th of July, 1798, about five
o’clock in the afternoon, Mr. Latham, a Fellow of the Royal Society,
then residing at Hastings, was surprised to see a crowd of people
running to the sea-side. Upon inquiry into the cause of this, he
learned that the coast of France could be seen by the naked eye, and
he immediately went down to witness so singular a sight. He distinctly
saw the cliffs extending for some leagues along the French coast, and
they appeared as if they were only a few miles off. They gradually
appeared more and more elevated, and seemed to approach nearer to the
eye. The sailors with whom Mr. Latham walked along the waters edge were
at first unwilling to believe in the reality of the appearance; but
they soon became so thoroughly convinced of it, that they pointed out
and named to him the different places which they had been accustomed to
visit, and which they conceived to be as near as if they were sailing
at a small distance into the harbour. These appearances continued for
nearly an hour, the cliffs sometimes appearing brighter and nearer, and
at other times fainter and more remote. Mr. Latham then went upon the
eastern cliff or hill, which is of considerable height, when, as he
remarks, a most beautiful scene presented itself to his view. He beheld
at once Dungeness, Dover cliffs, and the French coast all along from
Calais, Boulogne, &c., to St. Vallery, and, as some of the fishermen
affirmed, as far west as Dieppe. With the help of a telescope, the
French fishing-boats were plainly seen at anchor, and the different
colours of the land upon the heights, together with the buildings, were
perfectly discernible. Mr. Latham likewise states that the cape of land
called Dungeness, which extends nearly two miles into the sea, and is
about sixteen miles in a straight line from Hastings, appeared as if
quite close to it, and the vessels and fishing-boats which were sailing
between the two places appeared equally near, and were magnified to
a high degree. These curious phenomena continued “in the highest
splendour” till past eight o’clock, although a black cloud had for some
time totally obscured the face of the sun.
A phenomenon no less marvellous was seen by Professor Vince, of
Cambridge, and another gentleman, on the 6th of August, 1806, at
Ramsgate. The summits _v w x y_ of the four turrets of Dover Castle
are usually seen over the hill AB, upon which it stands, lying between
Ramsgate and Dover; but on the day above-mentioned, at seven o’clock in
the evening, when the air was very still and a little hazy, not only
were the tops _v w x y_ of the four towers of Dover Castle seen over
the adjacent hill AB, _but the whole of the Castle, m n r s, appeared
as if it were situated on the side of the hill next Ramsgate_, and
rising above the hill as much as usual. This phenomenon was so very
singular and unexpected, that at first sight Dr. Vince thought it an
illusion; but upon continuing his observations, he became satisfied
that it was a real image of the Castle. Upon this he gave a telescope
to a person present, who, upon attentive examination, saw also a
very clear image of the Castle as the Doctor had described it. He
continued to observe it for about twenty minutes, during which time the
appearance remained precisely the same; but rain coming on, they were
prevented from making any further observations. Between the observers
and the land from which the hill rises there was about six miles of
sea, and from thence to the top of the hill there was about the same
distance. Their own height above the surface of the water was about
seventy feet.
[Illustration: _Fig. 31._]
This illusion derived great force from the remarkable circumstance,
that the hill itself did not appear through the image, as it might have
been expected to do. The image of the castle was very strong and well
defined, and though the rays from the hill behind it must undoubtedly
have come to the eye, yet the strength of the image of the castle so
far obscured the background, that it made no sensible impression on the
observers. Their attention was of course principally directed to the
image of the castle; but if the hill behind had been at all visible,
Dr. Vince conceives that it could not have escaped their observation,
as they continued to look at it for a considerable time with a good
telescope.
[Illustration: _Fig. 32._]
Hitherto our aërial visions have been seen only in their erect and
natural positions, either projected against the ground or elevated
in the air; but cases have occurred in which both erect and inverted
images of objects have been seen in the air, sometimes singly,
sometimes combined, sometimes when the real object was invisible, and
sometimes when a part of it had begun to show itself to the spectator.
In the year 1793, Mr. Huddart, when residing at Allonby, in Cumberland,
perceived the inverted image of a ship beneath the image, as shown
in Fig. 32; but Dr. Vince, who afterwards observed this phenomenon
under a greater variety of forms, found that the ship, which was here
considered the real one, was only an erect image of the real ship,
which was at that time beneath the horizon, and wholly invisible.
[Illustration: _Fig. 33._]
In August, 1798, Dr. Vince observed a great variety of these aërial
images of vessels approaching the horizon. Sometimes there was seen
only one inverted image above the real ship, and this was generally the
case when the real ship was full in view. But when the real ship was
just begin beginning to show its top-mast above the horizon, as at A,
Fig. 33, two aërial images of it were seen, one at B inverted, and the
other in its natural position at C. In this case the sea was distinctly
visible between the erect and inverted images, but in other cases the
hull of the one image was immediately in contact with the hull of the
other.
Analogous phenomena were seen by Captain Scoresby when navigating
with the ship Baffin the icy sea in the immediate neighbourhood of
West Greenland. On the 28th of June, 1820, he observed about eighteen
sail of ships at the distance of ten or fifteen miles. The sun had
shone during the day without the interposition of a cloud, and its
rays were peculiarly powerful. The intensity of its light occasioned a
painful sensation in the eyes, while its heat softened the tar in the
rigging of the ship, and melted the snow on the surrounding ice with
such rapidity that pools of fresh water were formed on almost every
place, and thousands of rills carried the excess into the sea. There
was scarcely a breath of wind: the sea was as smooth as a mirror. The
surrounding ice was crowded together, and exhibited every variety, from
the smallest lumps to the most magnificent sheets. Bears traversed the
fields and floes in unusual numbers, and many whales sported in the
recesses and openings among the drift ice. About six in the evening, a
light breeze at N.W. having sprung up, a thin stratus or “fog bank,”
at first considerably illuminated by the sun, appeared in the same
quarter, and gradually rose to the altitude of about a quarter of a
degree. At this time most of the ships navigating at the distance
of ten or fifteen miles began to change their form and magnitude,
and when examined by a telescope from the mast-head, exhibited some
extraordinary appearances, which differed at almost every point of the
compass. One ship had a perfect image, as dark and distinct as the
original, united to its mast-head in a reverse position. Two others
presented two distinct inverted images in the air, one of them a
perfect figure of the original, and the other wanting the hull. Two
or three more were strangely distorted, their masts appearing of at
least twice their proper height, the top-gallant mast forming one-half
of the total elevation; and other vessels exhibited an appearance
totally different from all the preceding, being as it were compressed,
in place of elongated. Their masts seemed to be scarcely one-half of
their proper altitude, in consequence of which one would have supposed
that they were greatly heeled-to one side, or in the position called
careening. Along with all the images of the ships a reflexion of the
ice, sometimes in two strata, also appeared in the air, and these
reflexions suggested the idea of cliffs composed of vertical columns of
alabaster.
On the 15th, 16th, and 17th of the same month, Mr. Scoresby observed
similar phenomena, sometimes extending continuously through half the
circumference of the horizon, and at other times appearing only in
detached spots in various quarters. The inverted images of distant
vessels were often seen in the air, _while the ships themselves were
far beyond the reach of vision_. Some ships were elevated to twice
their proper height, while others were compressed almost to a line.
Hummocks of ice were surprisingly enlarged, and every prominent object
in a proper position was either magnified or distorted.
But of all the phenomena witnessed by Mr. Scoresby, that of the
_Enchanted Coast_, as it may be called, must have been the most
remarkable. This singular effect was seen on the 18th of July, when
the sky was clear, and a tremulous and perfectly transparent vapour
was particularly sensible and profuse: at nine o’clock in the morning,
when the phenomenon was first seen, the thermometer stood at 42°
Fahr.; but in the preceding evening it must have been greatly lower,
as the sea was in many places covered with a considerable pellicle
of new ice,--a circumstance, which, in the very warmest time of the
year, must be considered as quite extraordinary, especially when it
is known that 10° farther to the north no freezing of the sea at
this season had ever before been observed. Having approached on this
occasion so near the unexplored shore of Greenland that the land
appeared distinct and bold, Mr. Scoresby was anxious to obtain a
drawing of it; but on making the attempt he found that the outline
was constantly changing, and he was induced to examine the coast with
a telescope, and to sketch the various appearances which presented
themselves. These are shown, without any regard to their proper order,
in Fig. 34, which we shall describe in Mr. Scoresby’s own words: “The
general telescopic appearance of the coast was that of an extensive
ancient city abounding with the ruins of castles, obelisks, churches,
and monuments, with other large and conspicuous buildings. Some of
the hills seemed to be surmounted by turrets, battlements, spires,
and pinnacles; while others, subjected to one or two reflexions,
exhibited large masses of rock, apparently suspended in the air, at a
considerable elevation above the actual termination of the mountains to
which they referred. The whole exhibition was a grand phantasmagoria.
Scarcely was any particular portion sketched before it changed its
appearance, and assumed the form of an object totally different. It
was perhaps alternately a castle, a cathedral, or an obelisk; then
expanding horizontally, and coalescing with the adjoining hills, united
the intermediate valleys, though some miles in width, by a bridge
of a single arch, of the most magnificent appearance and extent.
Notwithstanding these repeated changes, the various figures represented
in the drawing had all the distinctness of reality; and not only the
different strata, but also the veins of the rocks, with the wreaths of
snow occupying ravines and fissures, form sharp and distinct lines,
and exhibited every appearance of the most perfect solidity.”
[Illustration: _Fig. 34._]
One of the most remarkable facts respecting aërial images presented
itself to Mr. Scoresby in a later voyage which he performed to the
coast of Greenland in 1822. Having seen an inverted image of a ship
in the air, he directed to it his telescope; he was able to discover
it to be his father’s ship, which was at the time below the horizon.
“It was,” says he, “so well defined, that I could distinguish by a
telescope every sail, the general rig of the ship, and its particular
character; insomuch, that I confidently pronounced it to be my father’s
ship, the _Fame_, which it afterwards proved to be; though, on
comparing notes with my father, I found that our relative position, at
the time, gave a distance from one another very nearly thirty miles,
being about seventeen miles beyond the horizon, and some leagues beyond
the limit of direct vision. I was so struck with the peculiarity of
the circumstance, that I mentioned it to the officer of the watch,
stating my full conviction that the _Fame_ was then cruising in the
neighbouring inlet.”
Several curious effects of the mirage were observed by Baron Humboldt
during his travels in South America. When he was residing at Cumana,
he frequently saw the islands of Picuita and Boracha suspended in the
air, and sometimes with an inverted image. On one occasion he observed
small fishing-boats swimming in the air, during more than three or
four minutes, above the well-defined horizon of the sea; and when they
were viewed through a telescope, one of the boats had an inverted
image accompanying it in its movements. This distinguished traveller
observed similar phenomena in the barren steppes of the Caraccas, and
on the borders of the Orinoco, where the river is surrounded by sandy
plains. Little hills and chains of hills appeared suspended in the
air, when seen from the steppes, at three or four leagues’ distance.
Palm-trees standing single in the Llanos appeared to be cut off at
bottom, as if a stratum of air separated them from the ground; and, as
in the African desert, plains destitute of vegetation appeared to be
rivers or lakes. At the Mesa de Pavona M. Humboldt and M. Bonpland _saw
cows suspended in the air_ at the distance of 1000 toises, and having
their feet elevated 3’ 20” above the soil. In this case the images were
erect, but the travellers learned from good authority that _inverted
images of horses had been seen suspended in the air_ near Calabozo.
In all these cases of aërial spectres, the images were directly above
the real object; but a curious case was observed by Messrs. Jurine and
Soret on the 17th September, 1818, where the image of the vessel was
on one side of the real one. About 10 P.M. a barque at the distance
of about 4000 toises from Bellerive, on the lake of Geneva, was seen
approaching to Geneva by the _left_ bank of the lake, and at the same
time an image of the sails was observed above the water, which, instead
of following the direction of the barque, separated from it, and
appeared to approach Geneva by the right bank of the lake, the _image_
moving from _east_ to _west_, while the _barque_ moved from _north_ to
_south_. When the image first separated from the barque they had both
the same magnitude, but the image diminished as it receded from it,
and was reduced to one-half when the phenomenon disappeared.
A very unusual example of aërial spectres occurred to Dr. A. P. Buchan
while walking on the cliff about a mile to the east of Brighton, on the
morning of the 28th of November, 1804. “While watching the rising of
the sun,” says he, “I turned my eyes directly towards the sea, just as
the solar disk emerged from the surface of the water, and saw the face
of the cliff on which I was standing represented precisely opposite to
me at some distance on the ocean. Calling the attention of my companion
to this appearance, we discerned our own figures standing on the summit
of the apparent opposite cliff, as well as the representation of the
windmill near at hand.
“The reflected images were most distinct precisely opposite to where
we stood, and the false cliff seemed to fade away, and to draw near
to the real one, in proportion as it receded towards the west. This
phenomenon lasted about ten minutes, or till the sun had risen nearly
his own diameter above the surface of the ocean. The whole then seemed
to be elevated into the air, and successively disappeared, giving an
impression very similar to that which is produced by the drawing up of
a drop-scene in a theatre. The horizon was cloudy, or perhaps it might
with more propriety be said that the surface of the sea was covered
with a dense fog of many yards in height, and which gradually receded
before the rays of the sun.”
An illusion of a different kind, though not less interesting, is
described by the Rev. Mr. Hughes in his Travels in Greece, as seen
from the summit of Mount Ætna. “I must not forget to mention,” says
he, “one extraordinary phenomenon, which we observed, and for which I
have searched in vain for a satisfactory solution. At the extremity
of the vast shadow which Ætna projects across the island, appeared a
perfect and distinct image of the mountain itself elevated above the
horizon, and diminished as if viewed in a concave mirror. Where or what
the reflector could be which exhibited this image, I cannot conceive;
we could not be mistaken in its appearance, for all our party observed
it, and we had been prepared for it beforehand by our Catanian friends.
It remained visible about _ten_ minutes, and disappeared as the shadow
decreased. Mr. Jones observed the same phenomenon, as well as some
other friends with whom I conversed upon the subject in England.”
It is impossible to study the preceding phenomena without being
impressed with the conviction, that nature is full of the marvellous,
and that the progress of science and the diffusion of knowledge
are alone capable of dispelling the fears which her wonders must
necessarily excite even in enlightened minds. When a spectre haunts
the couch of the sick, or follows the susceptible vision of the
invalid, a consciousness of indisposition divests the apparition of
much of its terror, while its invisibility to surrounding friends
soon stamps it with the impress of a false perception. The spectres
of the conjuror, too, however skilfully they may be raised, quickly
lose their supernatural character; and even the most ignorant beholder
regards the modern magician as but an ordinary man, who borrows from
the sciences the best working implements of his art. But when, in the
midst of solitude, and in situations where the mind is undisturbed
by sublunary cares, we see our own image delineated in the air, and
mimicking in gigantic perspective the tiny movements of humanity;--when
we see troops in military array performing their evolutions on the very
face of an almost inaccessible precipice--when, in the eye of day, a
mountain seems to become transparent, and exhibits on one side of it a
castle which we know to exist only on the other; when distant objects,
concealed by the roundness of the earth, and beyond the cognisance of
the telescope, are actually transferred over the intervening convexity
and presented in distinct and magnified outline to our accurate
examination;--when such varied and striking phantasms are seen also by
all around us, and therefore appear in the character of real phenomena
of nature, our impressions of supernatural agency can only be removed
by a distinct and satisfactory knowledge of the causes which gave them
birth.
It is only within the last forty years that science has brought these
atmospherical spectres within the circle of her dominion; and not only
are all their phenomena susceptible of distinct explanation, but we can
even reproduce them on a small scale with the simplest elements of our
optical apparatus.
[Illustration: _Fig. 35._]
In order to convey a general idea of the causes of these phenomena, let
ABCD, Fig. 35, be a glass trough filled with water, and let a small
ship be placed at S. An eye situated about E, will see the top-mast
of the ship S, directly through the plate of glass BD. Fix a convex
lens _a_ of short focus upon the plate of glass BD, and a little above
a straight line SE joining the ship and the eye; and immediately above
the convex lens a place _a_ concave one _b_. The eye will now see,
through the convex lens _a_, an _inverted_ image of the ship at S´,
and through the concave lens _b_, an erect image of the ship at S´´,
representing in a general way the phenomena shown in Fig. 33. But it
will be asked, where are the lenses in nature to produce these effects?
This question is easily answered. If we take a tin tube with glass
plates at each end, and fill it with water, and if we cool it on the
outside with ice, it will act like a _concave_ lens when the cooling
effect has reached the axis; and, on the other hand, if we heat the
same tube filled with water, on the outside, it will act as a _convex_
glass. In the first case the density of the water diminishes towards
the centre, and in the second it increases towards the centre. The
very same effects are produced in the air, only a greater tract of air
is necessary for showing the effect produced, by heating and cooling it
unequally. If we now remove the lenses _a_, _b_, and hold a heated iron
horizontally above the water in the trough ABC, the heat will gradually
descend, expanding or rendering rarer the upper portions of the fluid.
If, when the heat has reached within a little of the bottom, we look
through the trough at the ship S in the direction ES´, we shall see
an inverted image at S´, and an erect one at S´´; and if we hide from
the eye at E all the ship S, excepting the top-mast, we shall have an
exact representation of the phenomenon in Fig. 33. The experiment will
succeed better with oil in place of water; and the same result may be
obtained without heat, by pouring clear syrup into the glass trough
till it is nearly one-third full, and then filling it up with water.
The water will gradually incorporate with the syrup, and produce, as
Dr. Wollaston has shown, a regular gradation of density, diminishing
from that of the pure syrup to that of the pure water. Similar effects
may be obtained by using masses of transparent solids, such as glass,
rock-salt, &c.
Now it is easy to conceive how the changes of density which we can
thus produce artificially may be produced in nature. If, in serene
weather, the surface of the sea is much colder than the air of the
atmosphere, as it frequently is, and as it was to a very great degree
during the phenomena described by Mr. Scoresby, the air next the sea
will gradually become colder and colder, by giving out its heat to
the water; and the air immediately above will give out its heat to
the cooler air immediately below it, so that the air from the surface
of the sea, to a considerable height upwards, will gradually diminish
in density, and therefore must produce the very phenomena we have
described.
[Illustration: _Fig. 36._]
The phenomenon of Dover Castle seen on the Ramsgate side of the hill,
was produced by the air being more dense near the ground and above the
sea than at greater heights, and hence the rays proceeding from the
castle reached the eye in curve lines, and the cause of its occupying
its natural position on the hill, and not being seen in the air, was
that the top of the hill itself, in consequence of being so near the
castle, suffered the same change from the varying density of the
air, and therefore the castle and the hill were equally elevated and
retained their relative positions. The reason why the image of the
castle and hill appeared erect was, that the rays from the top and
bottom of the castle had not crossed before they reached Ramsgate; but
as they met at Ramsgate, an eye at a greater distance from the castle,
and in the path of the rays, would have seen the image inverted. This
will be better understood from the preceding diagram, which represents
the actual progress of the rays, from a ship SP, concealed from the
observer at E by the convexity of the earth PQE. A ray proceeding from
the keel of the ship P is refracted into the curve line P _c x c_ E,
and a ray proceeding from the top-mast S, is refracted in the direction
S _d x d_ E, the two rays crossing at _x_, and proceeding to the eye
E with the ray from the keel P uppermost; hence the ship must appear
inverted as at _s p_. Now if the eye E of the observer had been placed
nearer the ship as at _x_, before the rays crossed, as was the case at
Ramsgate, it would have seen an erect image of the ship raised a little
above the real ship SP. Rays S _m_, S _n_, proceeding higher up in the
air, are refracted in the directions S _m m_ E, S _n n_ E, but do not
cross before they reach the eye, and therefore they afford the erect
image of the ship shown at _s´ p´_.
The aërial troopers seen at Souterfell were produced by the very
same process as the spectre of Dover Castle, having been brought by
unequal refraction from one side of the hill to the other. It is not
our business to discover how a troop of soldiers came to be performing
their evolutions on the other side of Souterfell; but if there was then
no road along which they could be marching, it is highly probable that
they were troops exercising among the hills in secret, previously to
the breaking out of the rebellion in 1745.
The image of the Genevese barque which was seen sailing at a distance
from the real one, arose from the same cause as the images of ships in
the air; with this difference only, that in this case the strata of
equal density were vertical or perpendicular to the water, whereas,
in the former cases they were horizontal or parallel to the water.
The state of the air which produced the lateral image may be produced
by a headland or island, or even rocks, near the surface, and covered
with water. These headlands, islands, or sunken rocks being powerfully
heated by the sun in the daytime, will heat the air immediately above
them, while the adjacent air over the sea will retain its former
coolness and density. Hence there will necessarily arise a gradation
of density varying in the same horizontal direction, or where the
lines of equal density are vertical. If we suppose the very same state
of the air to exist in a horizontal plane which exists in a vertical
plane, in Fig. 36, then the same images would be seen in a horizontal
line, viz., an inverted one at _s p_, and an erect one at _s´p´_. In
the case of the Genevese barque, the rays had not crossed before they
reached the eye, and therefore the image was an erect one. Had the
real Genevese barque been concealed by some promontory or other cause
from the observation of Messrs. Jurine and Soret, they might have
attached a supernatural character to the spectral image, especially if
they had seen it gradually decay, and finally disappear on the still
and unbroken surface of the lake. No similar fact had been previously
observed, and there were no circumstances in the case to have excited
the suspicion that it was the spectre of a real vessel produced by
unequal refraction.
The spectre of the Brocken and other phenomena of the same kind, have
essentially a different origin from those which arise from unequal
refraction. They are merely shadows of the observer projected on dense
vapour or thin fleecy clouds, which have the power of reflecting much
light. They are seen most frequently at sunrise, because it is at that
time that the vapours and clouds necessary for their production are
most likely to be generated; and they can be seen only when the sun
is throwing his rays horizontally, because the shadow of the observer
would otherwise be thrown either up in the air, or down upon the
ground. If there are two persons looking at the phenomenon, as when
M. Haue and the landlord saw it together, each observer will see his
own image most distinctly, and the head will be more distinct than the
rest of the figure, because the rays of the sun will be more copiously
reflected at a perpendicular incidence: and as, from this cause, the
light reflected from the vapour or cloud becomes fainter farther from
the shadow, the appearance of a halo round the head of the observer is
frequently visible. M. Haue mentions the extraordinary circumstance
of the two spectres of him and the landlord being joined by a _third
figure_, but he unfortunately does not inform us which of the two
figures was doubled, for it is impossible that a person could have
joined their party unobserved. It is very probable that the new spectre
forms a natural addition to the group, as we have represented it in
Fig. 30; and, if this was the case, it could only have been produced by
a duplication of one of the figures produced by unequal refraction.
The reflected spectre of Dr. Buchan standing upon the cliff at
Brighton, arose from a cause to which we have not yet adverted. It was
obviously no shadow, for it is certain, from the locality, that the
rays of the sun fell upon the face of the cliff and upon his person at
an angle of about 73° from the perpendicular, so as to illuminate them
strongly. Now, there are two ways in which such an image may have been
reflected, namely, either from strata of air of variable density, or
from a vertical stratum of vapour, consisting of exceedingly minute
globules of water. Whenever light suffers refraction, either in passing
at once from one medium into another, or from one part of the same
medium into another of different density, a portion of it suffers
reflexion. If an object, therefore, were strongly illuminated, a
sufficiently distinct image, or rather shadow of it, might be seen by
reflexion from strata of air of different density. As the temperature
at which moisture is deposited in the atmosphere varies with the
density of the air, then at the same temperature moisture might be
depositing in a stratum of one density, while no deposition is taking
place in the adjacent stratum of a different density. Hence there would
exist, as it were in the air, a vertical wall or stratum of minute
globules of water, from the surface of which a sufficiently distinct
image of a highly illuminated object might be reflected. That this
is possible may be proved by breathing upon glass. If the particles
deposited upon the glass are large, then no distinct reflection will
take place; but if the particles be very small, we shall see a distinct
image formed by the surface of the aqueous film.
The phenomena of the Fata Morgana have been too imperfectly described
to enable us to offer a satisfactory explanation of them. The aërial
images are obviously those formed by unequal refraction. The pictures
seen on the sea may be either the aërial images reflected from its
surface, or from a stratum of dense vapour, or they may be the direct
reflexions from the objects themselves. The coloured images, as
described by Minasi, have never been seen in any analogous phenomena,
and require to be better described before they can be submitted to
scientific examination.
The representation of ships in the air by unequal refraction has no
doubt given rise in early times to those superstitions which have
prevailed in different countries respecting “phantom ships,” as Mr.
Washington Irving calls them, which always sail in the eye of the
wind, and plough their way through the smooth sea, where there is
not a breath of wind upon its surface. In his beautiful story of the
storm ship, which makes its way up the Hudson against wind and tide,
this elegant writer has finely embodied one of the most interesting
superstitions of the early American colonists. The Flying Dutchman had,
in all probability, a similar origin; and the wizard beacon-keeper of
the Isle of France, who saw in the air the vessels bound to the island
long before they appeared in the offing, must have derived his power
from a diligent observation of the phenomena of nature.