Andy YOUNG is, of course, absolutely right. When we examined the North Sea sightings in 1993/1994 it didn't dawn on us that very exceptional conditions would be required for a specular reflection of a ground-based light source to show up as a round spot near the zenith. In fact, it was only in 2006 that Joël BAVAIS' spectacular photo of a star-shaped reflection made that clear to us.
So in order to explain the October 20, 1993 observations from ships and oil platforms in the North Sea, we would require exceptional conditions (thin layer + crystals perfectly aligned horizontally with average inclination no more than a couple of minutes of arc). Weather data for October 20 only specify a temperature of 9° C, wind from the southeast and 2/8 to 3/8 cloud coverage at the beginning of the sightings with clouds finally obstructing the lights from view. Nothing is said about wind speed, but there's a statement by a passenger from one of the ships informing us that "there was too much movement to take photographs", suggesting that there was at least some wind at the time of the observations.
Left is the engraving Andrew YOUNG refers to. Initially published in L'Astronomie 9, 41-42, it depicts a mirrored image of the Eiffel Tower as reportedly observed on December 6, 1889, at 9 a.m. local time.
[Image gleaned from gallica.bnf.fr]
Below is an English translation of the report doctor Charles-Henri MARTIN, a friend of the observers, sent to French astronomer Camille FLAMMARION, publisher of L'Astronomie and prolific author of more than 50 titles.
"Last Friday 6 December, at about 9 o' clock in the morning, City Engineer Lion, Mr. Didier and Mr. Laureau were at the Place du Trocadéro, on the corner of Kléber lane. From this point one can see the top half of the Eiffel Tower, behind the left part of the buildings from the Palais du Trocadéro.
At that time the weather was bright and the sun was shining. All of a sudden, the observers noticed that the tower was surmounted, points touching, by a second, upside-down tower, oriented in the same axis as the real one. This reversed image was very sharp, to such a degree that one could clearly distinguish the peak, the ball at the end, and all the cross-beams from the upper part of the tower; the second platform could also be distinguished; the central part was less clear, and the base had vanished, lost in the haze higher up.
Very close and behind the real Eiffel Tower, over the Champ-de-Mars, one could notice, especially on the right, towards the West, a low cloud, sitting at a level with the middle part of the tower, very bright, shining like silver, of a flake-like appearance. The apparition remained very sharp during the few minutes the observers were on the square. It is said that it was still visible after they had walked past the buildings of the Trocadéro to the fountain. The sun was shining through the haze, to the left of the tower, almost on a level with the second floor."
A very interesting meteorological phenomenon indeed, and we are delighted to bring it to the attention of our readers. The conditions in which it occurred are known. The layer of air immediately on top of the tower served as a mirror. At ground level the temperature was 0°. At the top of the tower it was -3°,5. Wind Northeast and weak.
Another engraving of what appears to have been a similar case of extraordinary aerial reflection was published in FLAMMARION's L'atmosphère et les grands phénomènes de la nature. It shows another part of the French capital mirrored in the sky. This display is said to have occurred some twenty years earlier during the early hours of December 14, 1869, between 3 and 4 a.m.
Image scanned from p. 44 of Het Weer (Ed. De Lantaarn, Amsterdam, 1982)]
The text accompanying this engraving reads as follows:
Hardly a season goes by without the papers reporting on a sighting of a superior mirage produced in our moderate regions, like for instance the reflection of a city in the sky; but, in general, the images are transient and diffuse. In 1869 we had one such event in Paris, all the more stranger because it occurred by moonlight. In the night of 14 December 1869, between three and four o' clock in the morning, people returning from the soirée and crossing the bridges and the river banks, were witnesses to this curious phenomenon. The moon was shining beautifully, but the moon and the sky were fogged with clouds that seemed to be lit by the light of the aurora borealis. It was a nice example of a superior mirage, and for more than an hour only a few rare spectators were able to examine this interesting spectacle.
Paris, its palaces, its monuments and the river showed up in the clouds that masked the sky, but the images were reversed, as if someone had placed a giant plate of glass over Paris. Depicted were the Pantheon, Les Invalides, Notre-Dame, the Palais du Louvre and the Tuileries. From the Pont des Arts you could see the Seine, the bridges, the spires of the Saint-Clotilde, the Place de la Concorde, the Champs-Elysées and the Palais de l'Industrie, that, silvered by the moonlight, produced a pink image of an indescribable nature.
The lack of high-quality data and independent eye-witness accounts raises doubts as to the accuracy of these reports. If the phenomenon is real, one would expect someone to have captured it on photo or video in later years. Yet the only photographic evidence of ground-based features mirrorred in ice clouds (not mirages!) are photos of pillar-shaped reflections of bright lights such as can be seen in these two shots:
A cloud of ice-crystal plates at 400 m (1,300 ft) reflects the city-lights of Philadelphia. Photo taken by David WEI from Plymouth Meeting on November 19, 2008. See our case analysis for more details.
A similar display photographed at Xiamen, China, on July 9, 2010". [Image borrowed from whatsonxiamen.com].
Leaving aside anecdotal evidence from earlier centuries describing phantom armies and ghost ships in the sky, we found only one "recent" report of a crisp, reversed image of a ground-based feature (in casu a tall building) identical to what is depicted in the engravings published above. Unfortunately, the date is not given, but the story, as told by the observer, has been on the Internet for at least fifteen years. We quote:
One evening my wife and I were returning to work after dinner. (That is what happens when you start your own company!) Off to the right I saw a multi-story building where none existed a couple of hours earlier! I asked my wife, "when did they build that!" to which she responded with a mild profanity. There it was - a tall, well lit building with bricks, windows, and lights along the roof line shining down on the sides. We turned right to investigate this miracle of construction. But, as we approached the structure, it began to move! Soon it literally took off into the air, flying out over highway 183. Keep in mind, this thing was not a blur of lights. It was a flying building. Realizing it was some sort of illusion, we gave chase and ended up heading west ("north") on 183. We pulled into a parking lot when we had a really good view of this hovering building and we jumped out to get a better look. There was no clearly visible bottom and it seemed to be several hundred feet up, but it was quite clear. If there had been a person standing in one of the dark windows we could have easily seen him. Now for the discovery... Directly below the flying building was another building. This structure was identical except that there were no roof lights. There were, however, lights mounted on the ground pointing UP at the sides of the building. We were looking at a high quality reflection office or some sort of boundary layer. We watched in amazement until it eventually broke up. When it broke up, there was a convincing illusion of movement. It appeared as though several pieces darted away at remarkable speed. Now that I have seen such a reflection, I am certain that it explains a large number of the more mysterious sightings. Next time you fly at night, look out the window and notice how many of the lights below look really odd and are hard to identify. NOW IMAGINE SEEING ONE OF THOSE IN THE SKY, FLYING AROUND!
[Source: www.techlib.com; the author of the above account is Charles WENZEL from Austin, Texas. Mr. WENZEL is head of Wenzel Associates, Inc., a leading manufacturer of precision crystal oscillators and related radio frequency devices for the communications, navigation, military, and test equipment markets.]
We are reluctant to accept these narratives as factual. Their extreme rarity evokes errors of observation or mistakes that occurred during reporting or publishing. On the other hand, if these extraordinary reflections do really occur from time to time - and which is theoretically possible - this might explain a great deal of hitherto unexplained sightings of unusual aerial phenomena. A good enough reason for CAELESTIA to keep monitoring the literature for more reports of this type.