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How did the lighthouse at Pharos work?

How did the lighthouse at Pharos work?


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Was the ancient Greek pharos light house of ancient Alexandria, Egypt capable of creating light beams like a modern flash light?

Lots of websites which also includes ones from schools, colleges, universities, and museums say this.

I just want to know if these are all true.

Please explain to me the physics and chemistry behind this light beam feat of the ancient Greek Pharos lighthouse of ancient Alexandria, Egypt.


Was the ancient Greek pharos light house of ancient Alexandria, Egypt capable of creating light beams like a modern flash light?

No.

Historical descriptions

No one really knows any detail of the construction of the lighthouse or whether it originally had any lamp or fire at all

For example, the Ancient History Encyclopedia notes

The exact design of the lighthouse, unfortunately, is not made clear by ancient writers, with descriptions often being vague, confusing, and conflicting. Most sources do agree that the tower was white (making it more visible) and that it had three floors.

A fire, likely burning oil as wood was scarce, was kept at the top of the tower to make it visible at night, but whether this was so from the outset is debated by historians, largely because the earliest references to the Pharos in the works of ancient writers make no mention at all of a light. Later sources do describe the Pharos as a lighthouse and not merely a landmark tower useful only during daylight.

According to 1st-century CE Roman writer Pliny the Elder:

The cost of its erection was eight hundred talents, they say; and, not to omit the magnanimity that was shown by King Ptolemæus on this occasion, he gave permission to the architect, Sostratus of Cnidos, to inscribe his name upon the edifice itself. The object of it is, by the light of its fires at night, to give warning to ships, of the neighbouring shoals, and to point out to them the entrance of the harbour. (Natural History, 36.18)

Since early descriptions did not mention any kind of fire used at night it is not even certain that the original design was intended to be useful to sailors at night.


Modern Flashlights

Since the question asks about something constructed 2300 years ago I will mostly interpret "modern" as meaning anytime in the last century or two.

A modern flashlight has a relatively small source of light and typically either uses a parabolic reflector or a lens to produce a nearly parallel beam. Modern era lighthouses use Fresnel lenses but flashlights don't.

To be useful in a lighthouse, any directional beam requires a rotating mechanism so that the landmark can be visible from any direction as a periodic recurring flash of light.

Any mirror used at the Alexandria tower is likely to have been polished metal. I don't know of any accounts of a rotating parabolic mirror or lens of the rather huge size that would be needed to focus the light of a oil-powered fire sufficiently large to produce an amount of light that could be seen many kilometers away.


Websites

Lets examine the websites listed in the question.

softschools

It was reported that there was a large mirror inside, possibly made of polished bronze. The purpose of the mirror was to project a beam of light from the reflection of the fire.

Does not cite source of this report - therfore unreliable.

Wabash

There, according to reports, a large curved mirror, perhaps made of polished metal, was used to project the fire's light into a beam. It was said ships could detect the light from the tower at night or the smoke from the fire during the day up to one-hundred miles away.

Does not cite source of this report - therfore unreliable.

unmuseum

according to reports, a large curved mirror, perhaps made of polished bronze, was used to project the fire's light into a beam. It was said ships could detect the light from the tower at night or the smoke from the fire during the day up to one-hundred miles away.

Same wording but again no source cited - unreliable.

kidsgen

The mirror that was mounted at the top of the lighthouse could reflect light more than 35 miles off-shore. The scientists were fascinated by this mysterious mirror.

the beacon chamber, containing a curved mirror used to project a fire's light into a beam. Ships could detect the beam from the tower at night or the smoke from it could be seen during the day from up to 100 miles away.

Same wording but again no source cited - unreliable.

globalmarvels

By day mirrors reflected sunlight from top of the tower. by night however the light house became a true wounder to be behold. A flame was light producing a beam of light of extraordinary power.

At the peak of the lighthouse was a large curved mirror,perhaps made of polished bronze, that reflected the light of the sun at day, and project the fire's light into a beam at night.

Historians also suggest the mirrors were also used as a weapon to set enemy ships ablaze by reflecting the light of the sun into a strong beam.

Again no sources cited. Similar wording to all the others suggesting a common source

jslandor

The source of its light is much debated. Historians suggest a large curved mirror made of polished metal was positioned at its apex reflecting the sun by day while giant fires burned at night. The beam was so powerful it could be seen up to 30 miles away. Some claimed it could even be focussed on an enemy ship to set it ablaze

This web page does not cite sources or name the historians. It does mention the fictional book aimed at children: The Mirror of Pharos by J.S.Landor. which is the subject of the website as a whole.

I think this also must be counted as unreliable since there are no named sources we can check.

Maybe most or all of these websites are copying each other.

Since none of them cite sources, other than unnamed "historians" we must consider these descriptions as extremely unreliable.


To go into more details re. the mirror: Some of your links say that there are reports that the lighthouse had a curved mirror, which could even be used to set ships on fire or to spy on Constantinople (e.g. unmuseum). That these are always "reports" and no actual source is provided makes me suspect the evidence is rather slim.


This paper by Duggan and Akçay contains a number of references to medieval primary sources that mention a convex mirror in the lighthouse, in the footnote on p.401:

  • Plutarch mentions that concave mirrors exist and can be used to enlarge things (Plutarch is actually an ancient source and his quote is not directly relevant to Alexandria): De Faciae 17
  • Naser-e Khosraw in 1047 mentions that on top of the lighthouse there used to be a mirror that could be used to set ships on fire. Note that such a claim has also been made about Archimedes in Syracuse (and that Syracuse might also have had use for a lighthouse). The authors of the paper conjecture that a man who supposedly offered to fix the mirror may have been Alhazen who is also mentioned in one of the comments below
  • Benjamin of Tudela writes in the 12th century that there is a mirror on top of the lighthouse that can be used to look very far into the distance
  • similar claims (that the tower has a mirror on top that can be used to see approaching enemies) are made by Al-Maqrizi and Johann Schiltberger in the 14th century.
  • A 19th century source claims that the mirror was already removed between the 7th and the 8th century AD.

I have not tried to verify those sources, except Johann Schiltberger (his text is here and the paraphrase in the paper is accurate), and I have no idea if there are any other relevant primary sources.

If I understand the points made on p.400 correctly, the authors of the paper think that the mirror - if it actually existed - may have been a signalling device in a system similar to the roughly contemporary Byzantine beacon system.

In any case I think we can conclude that while there is little evidence that such a mirror actually existed in Alexandria, this is at least not something made up by modern authors. It may be a myth, but at least it is a myth with a very venerable history.


The famous Persian poet Hafez also mentions some "mirror of Alexander" in at least one of his poems and the context seems to imply that "Alexander's mirror" is curved like a wine cup and can be used to look into distant places.* Given that Hafez was born in the 14th century, lived far away from Alexandria, and there are many fanciful legends associated with Alexander and the Alexander Romance, this may be not much more than a legend. I am not even entirely sure that Hafez is referring to a mirror in a lighthouse.

In any case there are some Iranian academic papers on the subject (e.g. "Contemplation on a verse of Hafez" by A. Showghy Nobar and "Ayene-ye Sekandari" by M. Musavi), but I have not been able to access their full texts and I suspect they are written in Persian. English abstracts can be found via web search.


P.S. there is even a 17th century illustration of another 14th century poem of what Alexander's mirror may have looked like. Looks a lot like a mirror in a lighthouse to me, but minus the fire. Again, this does not mean that such a mirror actually existed. The illustrator may or may not have believed that such a mirror existed (cf illustrations of modern fantasy novels). If the illustrator actually believed in the existence of the mirror, his belief may still have been erroneous. (Note that Khosraw is a common Persian name and that Amir Khusraw Dihlavi whose poem is illustrated here and Naser-e Khosraw who is mentioned above are probably not related)


P.P.S. Thinking a bit more about this topic, it is somewhat intriguing that legends should mention the mirror and at the same time completely misunderstand what it might have been useful for.


*while a cup of wine can give you some impression of what happened to Darius III


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