Candle Clock

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The clock of the doors and the Jewish question

Introduction

The clock of the doors is identical to the candle clock of the monkey in terms of its mechanism and does not warrant a separate post. Just like the old joke about “The Elephant and the Jewish Question,” the clock of the doors has nothing to do with Jews,  which are not mentioned in the “The Book of Knowledge of Ingenious Mechanical Devices” even once. The phrase “The Elephant and the Jewish Question” is usually used to describe an annoying person who tries to link any event, however universal, to the Jewish people and their problems. I hope I’m not one of them, and I don’t have any convincing reason why I went out to check what we know about the Jews of Diyarbakır and Anatolia in the 12th Century. However, what I discovered is strange and exciting, and maybe it will interest you too.

The Candle Clock of the Doors” The Book of Knowledge of Ingenious Mechanical Devices, “Topkapi manuscript, 1206

How does it work?

Al-Jazari himself wrote:

” It is like the previous model, from which nothing is omitted except the keeper and the monkey. The additions are as follows: around the perimeter of the candle holder, fourteen doors are erected, each with two leaves. When a constant hour has passed from the lighting of the wick, a ball falls from the falcon’s beak, and the door opposite the falcon opens, and a figure emerges, [made] according to the choice of the craftsman.”

Anyone interested in the mechanism can go back and read my explanation of the monkey clock or the candle clock of the scribe. I will briefly explain the opening of the doors.

During combustion, the candle will shorten, and the force exerted by the weight will push the candle mount upwards at a constant rate that depends on the rate of combustion. To the bottom of the weight is attached another wire that runs over the pulley on which the bracket sits with 14 doors. These rotate as the candle burns. When the ball falls, it pushes the figure who opens a door and represents the time that has passed. This process repeats itself every hour.

The Jews in the 12th Century

The history of the Jewish people in the 12th Century is not similar in Ashkenazi communities and Muslim Spain. In Europe, the 12th Century began with the Rhineland massacres, a series of mass murders of Jews perpetrated by mobs of the People’s Crusade in 1096. The communities on the Rhine (Speyer, Worms, and Mainz) were destroyed. In 1146, in a repeat of the events of 1096, Crusaders preparing for the Second Crusade attacked and massacred Jewish communities along the Rhine. The 12th Century more or less ended with One of the worst Jews massacres of the Middle Ages, which took place in York in 1190. An angry mob trapped the city’s entire Jewish community inside the tower of York Castle. Many members of the community chose to commit suicide rather than be murdered or forcibly baptized by the attackers.

In Spain, on the other hand, Jewish people under Muslim rule experienced tolerance and integration. Some historians refer to this period as the “Golden Age” for the Jews, as more opportunities became available to them. That lasted from the days of the Caliphate of Cordoba to the small independent Muslim principalities and kingdoms of the Iberian Peninsula known as “taifas” and the process of the reconquest of Spain by the Christians. Social integration allowed Jews to advance significantly in new fields, philosophy and science. Some of them wrote poetry, primarily Hebrew poetry. They wrote about everything: poems about Zion and the people of Israel, but also poems about wine and women. I don’t think there’s a connection between the cultural flourishing in Diyarbakır and the Jewish flourishing in Muslim Spain, but it’s still intriguing. The Golden Age began in the 9th Century and ended in the 13th Century, but some of the more familiar figures were almost parallel to al-Jazari. For example, Maimonides was born in Cordoba in 1138, two years after al-Jazari, and died in Cairo in 1204, two years before him. Maimonides is a true polymath: one of the most prolific and influential Torah scholars of all generations, as well as a prominent philosopher of the Middle Ages, a scientist, and a physician. In his thirst for wisdom, he formed a study group and a friendship with Jabir ibn Aflah (a Muslim scholar) ‘s son, and they studied mathematics, medicine, and philosophy together. This must sound strange to those who live in Israel today and are familiar with the ultra-Orthodox opposition to secular studies. The “Kuzari” book, ” Book of Refutation and Proof on Behalf of the Despised Religion,” which I still managed to study in high school, was written by Rabbi Yehuda Halevi in this Century, and I must mention Rabbi Abraham Ibn Ezra, a 12-century poet, linguist, biblical commentator, and philosopher. He also worked in mathematics and astronomy. One of the lunar craters is named after him. Ibn Ezra’s most important mathematical work is in Hebrew: “The Book of the Unit,” which deals extensively with the decimal system and how it is used, thus preceding Fibonacci, the main contributor to the spread of this method in the Western world.

Did al-Jazari know the books they wrote or even heard about them? It is impossible to know, but the likelihood is extremely low.

Jews in Diyarbakır

In 1518, the Ottoman government conducted a census. There were 28 Jewish families and three single men in Diyarbakır. These are the first definitive data we have. After that, a continuous Jewish presence peaked in 1905, but apparently, the presence of Jews in Anatolia predates the Muslim conquest. According to traditions held by the Jews of Kurdistan, the Jews arrived in Kurdistan as early as the Salomon’s Temple period and are descendants of the Ten Tribes. As written in the book of  Kings:

” In the ninth year of Hoshea, the king of Assyria took Samaria, and carried Israel away unto Assyria, and placed them in Halah, and in Habor, on the river of Gozan, and in the cities of the Medes.”

Although we do not have a complete geographical identification, the name “Habur” has been preserved to this day as one of the Tigris tributaries located near the city of Zaxo (Arabic: زاخو), about 300 km from Diyarbakir. Later exiles to Babylon by Nebuchadnezzar, King of Babylon from the Kingdom of Judah, joined them. So it is very likely that there were Jews in Diyarbakir in al-Jazari’s day.

A Jewish delegation meeting with an Ottoman official

The Strange Story of David Alroy

Alroy was born a year before al-Jazari in Amadiya, Kurdistan. At first, I was confused because the historical name of Diyarbakır is Amida, but these are two different cities. Amadiya is located in northern Iraq, about 400 km southeast of Diyarbakir. David Alroy studied rabbinical literature with Hasdai, the exilarch, the leader of the Jewish community in Persian Mesopotamia, and Ali Gaon, the head of the Sanhedrin,  an assembly of elders appointed to sit as a tribunal in Baghdad. There is a claim that he was also well-versed in all the Books of Magic and sorcerers. I’m not sure what books are included, but it’s a bit like Chekhov’s gun, which appears in the first act, firing in the third. I have already mentioned Benjamin of Tudela, and not for the better. He wrote:

” David Alroy took upon him to rebel against the King of Persia [in 1163] ; for which purpose he gathered together all the Jews on the Mountains of Haphton, and from other Nations, to go to lay Siege to Jerusalem A great Part therefore of the Jews had Faith in; him, calling, him their Messiah. As soon as the King of Persia heard of this Matter, he commanded him to be brought before him. The King asked him: “Are thou the King of the Jews?” He answered and said, “I am,” The King then called to his Guards, and commanded him immediately to be apprehended, and led away to prison in the City of Dabastan. Three Days after this, as the King was sitting together with his Princes and Chief Minitiers, deliberating about the Jew Rebellion, behold David, having made his Escape from prison and approached and stood before him. The King looked at him and enquired, “Who brought thee hither?” He answered: “My own wisdom, and my own Subtilty because I fear neither thee nor any of thy Servants.” At which the King cried out: “Seize him!” But his servants said: “We see him not, but only hear the sound of his voice.”

Alroy then crosses the river on his handkerchief, and the King’s servants are unable to catch him in their boats. The King threatened to kill all the Jews in his kingdom. The frightened Jewish community threatened Alroy with a total exclusion from the Jewish community (“HEREM”). “In the end, David Alroy was killed in his bed while sleeping.

The story has legendary elements (seeing and not being seen, walking on water) absent in the description of Alroy’s contemporary, Al-Samawʾal ibn Yaḥyā al-Maghribi, who converted to Islam. To me, comparing the stories is less important than the passage describing the Baghdad Jews’ yearning for redemption:

“In this letter [a letter that two men forged in the name of David Alroy], they announce to the Jews of Baghdad the coming of the redemption they have been waiting for generations, in which they determine the night when they will all fly to Jerusalem, the holy city. Although the Jews of Baghdad were proud of their wisdom and strength of mind, they nevertheless tended to believe in this thing. Their wives brought all their possessions and jewelry to these two men so that they could divide all the property as they saw fit. In this way, the Jews wasted all their possessions. They wore green clothes and gathered that night on the rooftops of the houses, eagerly awaiting the moment when they would fly on the angels’ wings straight to Jerusalem. The women raised their voices in tears because they feared that they themselves would fly first before their children or the babies they were breastfeeding, and then these babies would suffer hunger.”

It is pretty clear that the Crusades and the instability in Palestine and nearby countries resonated strongly with some Eastern Jews, who saw them as precursors of redemption. The fantastic picture of the preparations for the flight and the heartbreak of the morning after also appear in other sources. Was all this commotion the talk of the day in Diyarbakir? This time not in distant Cordoba but in neighboring Amadiya,? We don’t know; even if it did, it must have been a minor event in al-Jazari’s world.

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The monkey’s candle clock and Falcons

Introduction

The monkey’s candle clock is very similar to the scribe candle clock and does not justify a post. However, the clock includes a Falcon. It made me go back and see what animals reside in Al-Jazari’s book. There are quite a few: an elephant, a lion, and a monkey. You can check how knowledgeable you are in the book if you know where the lion is hiding? (Unfortunately, there are no prizes for correct answers). There are some unidentified birds, a fish with no name, an ox or a donkey, al-Jazari gave no details, but used دابّة – daba which means an animal as well as two cows. On the more exotic side, there are five dragons (!) six peacocks (!!), and the champions of appearances in the book, to my great surprise, are seven Falcons. We have another perspective on Falcons and their special place in the Artuqid court from Usama ibn Munqidh(أسامةبنمنقذ), a medieval poet, writer, knight, and diplomat. I read his book “The Book of Contemplation” (in Hebrew, many thanks to Dr. Ella Almagor for her beautiful translation). There are numerous hunting stories, including falcons, at the court of the Emir Arslan, the father of Nur al-Din Muhammad, who hired al-Jazari. This will be the focus of this post.

Monkey’s Candle Clock Topkapi Manuscript, 1206

How does it work?

Al-Jazari wrote himself:

“The [following] are made as described previously: the candle-holder, the sheath, and the falcon; the two pulleys and the weight in the center of the interior of the sheath; the channel which covers the ball’s channel, inside which is the ball’s channel; the balls.”

Donald Hill, the book translator, and annotator, devoted to this chapter only a few lines, without a drawing, and wrote that the mechanism is the same as the scribe candle clock except for the vertical movement and not circular.  Still, I am briefly repeating the technical explanation, which as always, will be colored in blue, so anyone who is not interested in pulleys or balancing weight can skip those bits. The drawing below is by the book translator and annotator, Donald R. Hill [of the scribe candle clock] modified by me:

A drawing of the mechanism by Donald Hill with my modifications

The candle is placed on a holder inside a brass sheath, and only the wick protrudes through a hole in the cap. A long rod is soldered to the bottom of the holder. The rod runs through the main weight so that the weight is free to move up and down. Two strings are connected to the bottom of the rod and through two pulleys to the main weight. The latter is relatively heavy, slightly more than one kilogram. At nightfall, the wick is lit, at that time, the candle is in full size, the rod reaches its lowest point, and the main weight reaches its highest position. As the candle is consumed, the main weight will descend exerting force, through the pulleys, on the holder upward, and the holder and rod will go up at a constant rate, depending on the rate of the combustion.

To the bottom of the weight, another string is attached, through a pulley,  connected to the bottom of the rod on which the monkey sits. As the candle is consumed, the monkey will rise and point at the tick marks. There are 218 tick marks, and each represents 4 minutes and in total 14.5 hours Diyarbakir in the middle of the winter. The holder pulls the ball’s channel up, and every hour the highest ball in the channel has risen until it is level with the hole in the back of the falcon’s head, at which point it rolls out and falls from the falcon beak.

 

Usama ibn Munqidh

“The Book of Contemplation (كتابالاعتار, literally a  Book of learning by example) is an autobiographical book written by Usama ibn Munqidh, an Arab Syrian scholar and soldier of the 12th century, a son of the Munqidh, a noble Bedouin family that controlled the fortress in Shaizar in northern Syria.

Usama was a worrier and a hunter, but also a poet, a passionate book collector, and a diplomat with charm. He was born in 1095 in Shaizar, where he was educated and lived until 1131. When the men of the Shaizar did not fight the Crusaders or other opponents, they were hunting. Syria, in the 12th century, was heaven for hunters. I thought of rabbits, wild boars, and water birds, but to my surprise, there were also bears, lions, and tigers. The use of falcons and hawks was widespread. In 1162, when he fought alongside Nur ad-Din with the Crusaders of Antioch, he met Arslan, The Artuqid Emir. Upon the end of the battle, Arslan invited him to join him in the city of Hasankeyf, the home of the Artuqids, before they took over Diyarbakir. In the next decade, up to 1174, he spent hunting and writing in the Artuqid courtyard. The fourth section of his book is dedicated to hunting stories, and I’ll tell a little about what I learned about hunting with falcons and other birds of prey.

On Falcons and Falconry

Falconry is the art of using Falcons or the other birds of prey to hunt. Evidence suggests that falconry may have begun in Mesopotamia, with the earliest accounts dating to approximately 2,000 BC. Hunting with Falcons and hunting, in general, were a popular pastime in the period of the Umayyad and Abbasid Caliphates and were beloved also in the Artuqid Palace. Usama opens the hunting stories like this:

“I have in the above given those accounts of warfare and those experiences I had in battles, fights, and adventures which I could remember and which time with its rolling years did not make me forget. For my life has been prolonged, and I have for some time now been living in isolation and seclusion. Besides, oblivion is a heritage the antiquity of which goes back to our father, Adam (Peace be upon him!)  I shall now devote a chapter to what I have witnessed and partaken of in the field of hunting, be it the chase or falconry. Some of these experiences I had in Shaizar when I was still in the early part of life…and still others I had in Diyar-Bakr with al-Amir Fakhr al-Din Qara-Arslan ibn-Dawud  ibn-Urtuq (may Allah’s mercy rest upon his soul!).”

The great love for hunting is manifested through the story of his father, who was the ruler of Shaizar and gave up his throne:

“As for my hunting experiences in Shaizar, they were in the company of my father (may Allah’s mercy rest upon his soul!) Who was extremely fond of the chase, always talking about it and about collecting birds of prey, considering no amount of expense too great for the satisfaction of his curiosity in this sport…To him, the chase was in accordance with the following traditional saying: “Air ye your hearts so that they can better retain the word of Allah!” In fact, I never saw anything like his hunting and his ability to organize parties for it.”

An Arab-Syrian Gentleman and Warrior in the Period of the Crusades: Memoirs of Usama Ibn-Munqidh – Philip K. Hitti, 1929

The book is not a guide for the Falconer, but the stories contain a lot of practical information, for example, how did they hunt the falcons?

“All that was necessary was to have a stone house built to the height of a man. It would then be covered with branches concealed under hay and grass, with an opening. The trapper would then secure a pigeon, perch it on a stick, binding its two legs tightly to the stick, and display the pigeon from an opening, as a lure. As he moves the stick up and down, the pigeon flutters its wings. Seeing it, the falcon turns down and pounces on it to seize it. As soon as the hunter feels the falcon, he pulls the stick back to the opening, stretches out his hand, and seizes the two legs of the falcon.”

There are plenty of stories, but the story of al-Yahshur, an exceptional falcon demonstrates the unique relationship between the Muslim nobility and the predatory birds used for hunting:

Between Osama’s father and the sons of Rubal, the ruler of Armenia was a relation of friendship, and every year they would send him several falcons. One year a young broad like a saker [A falcon native of Southern Europe and Asia] arrived, but it could not keep up with the other falcons in flight, yet the falconer Ghana said, “Among all the falcons there is none like this young one, It will let no game escape it”. We could not at first believe him, but for the next thirteen years, al-Yahshur was the king of the hunting birds in Shaizar. The special relationship between his father and al-Yahshur can be seen here:

“When we entered the house, my father would say, “Fetch me a bowl of water.” They would fetch him one, and he would offer it to the falcon [al-Yahshur] while it was still on his wrist (may Allah’s mercy rest upon his soul!). The falcon would drink it. In case it wanted a bath, it would shake its beak in the water. My father would then order that a big basin full of water be brought and would offer it to the falcon… when it would get out of the water. My father would put it on a large wooden perch, especially made for it and would bring near it a brazier of live coal; and after it was combed and rubbed with oil” until it was dry, a folded piece of fur would be placed by it. The falcon would go down to it and sleep. It would remain among us sleeping on the fur until late in the night, at which time my father would want to retire into the harem’s apartment. He would then say to one of us, “Carry the falcon.” And the falcon would be carried as it lay sleeping on the fur until it was placed near the bed of my father (may Allah’s mercy rest upon his soul!).”

My love, M. says that I cannot tell about hunting with birds of prey without refereeing my readers to the movie about Aisholpan:

A young Mongolian girl who hunts with a golden eagle. This is, before anything else, a story about the power of a young woman who has managed to change Mongolians traditions. However, this is also a story about the deep connection between the hunter and his hunting bird. This is why there is no surprise in the number of falcons that penetrated al-Jazari’s machines.

A miniature of a falconer, North France, 1180.

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The Candle Clock of the Swordsman

Introduction

Candle clock is an ancient device for measuring the passage of time. The earliest reference is a Chinese poem by You Jiangu (AD 520). It appears in Wikipedia and other places, but I couldn’t find the poem itself, any help would be appreciated. These were simple clocks that were based on the relatively stable burning rate of candles. Linear graduation specified the elapsed time. All four candle clocks by al-Jazari are complex, full of inventions, a daring leap comparing to the classical candle clocks. In the clock of the Swordsman, the falcon emits a bronze ball every hour, so that the number of accumulated balls indicates the number of hours passed from sunset, at the same time the swordsman swings his sword and clips the top of the wick.

The Swordman Candle Clock, a Manuscript from 1315 Syria.

How does it work?

Al-Jazari opens the chapter of the candle clock of the swordsman with these words:

“I say that I have never come across a work by anyone on candle-clocks and have never seen a completed [example of such a] clock. I heard tell, however, of a candle-holder with a brass candlestick on it in which was a wax candle whose wick went through a hole in a cross-piece at the top of the brass candlestick. Near the foot of the candlestick was the head of a lion. When a constant hour had passed from the lighting of the candle, a ball fell from the mouth of the lion.”

The clock al-Jazari built was his version to the clock in the tale. The technical explanation, as always, will be colored in blue, so anyone who is not interested in balancing weights or bayonet mounts can skip those bits.

On the right side, the swordsman clock, Topkapi manuscript, 1206, with my explanatory captions. On the left is a three-dimensional sketch of the same clock based on the drawing by Donald Hill.

The massive candle, a height of about 40 centimeters (a span- شِبْر and a half) and almost four centimeters in diameter is standing on a cast bronze base. On the base, there is a brass sheath. The sheath is not a perfect circle but has two “lips” forming the ball channel, containing fourteen bronze balls. The candle alone blocks the balls. A heavy balancing weight of ~ 1.2 kg is connected through a pulley system. The weight guarantees that the bronze base and the candle are being pushed upward all the time. The length of the candle prevents the base from rising. The burning rate of the candle is measured meticulously, and the height of the candle is calculated so that it is suitable for sixteen hours of combustion, in practice, it would only burn for fourteen hours.

When the candle is lit at nightfall, the fire melts the wax, and after one hour the candle is shorter by 1/16. The weight will go down by this amount, and the base would go up, and the candle does not block any longer the lower ball. The ball is released and falls into the pouch attached to the string which is connected to the extension of the hand of the slave. As a result, the slave strikes the wick with his sword and cuts off the burnt-away section. The ball then rolls down and goes into the falcon’s head and then falls into the pedestal of the candle-holder. This happens at every hour until the end of the night

The part of the black slave and his sword is less detailed in my opinion, and its construction will require more experimentation and adjustments. Al-Jazari himself warns the reader that ” This movement [was perfected] after arranging and calculating and [after] repeated trials.”

Al-Jazari worked in the 12th century almost six centuries before Joseph Priestley discovered Oxygen, wax chemistry was also unknown at his time, and so was the understanding of Capillary Action. Despite this, his strong understanding of various materials, from working and experimenting, brings him to a few insights that we can now explain with the science we have learned. For example, al-Jazari requested that the candle will be made of pure wax. Candles can be prepared from natural fat, beeswax, whale fat, oil derivatives, and more. The rate of combustion depends on the combustion material, and as the material is more uniform, the rate of the combustion will be more uniform. He determines the weight of the wick, six grams. The wax is rising in the wick by capillary action, and therefore, various wicks will have different burning rate and would alter the time measurement.

One last thing, quite insignificant for the clock but interesting never the less. The candle cover was designed to replace candles comfortably. This method of mechanical attachment is known as “Bayonet mount,” and despite its exotic name, it is a useful technique of attachment  to this day, for example in camera lenses or electric lights and includes a cylindrical male side with one or more radial pins, and a female receptor with matching L-shaped slots and with spring(s) to keep the two parts locked together:

The source of the peculiar name is the use of soldiers in this type of connection to quickly attach bayonets at the ends of their rifles, but the first documented bayonet mount is undoubtedly al-Jazari book in this chapter.

My chemistry teacher and Michael Faraday

In 1972, I was sixteen and studied in the Tichon Hadash in Tel-Aviv. It was the only year we studied chemistry. To my shame, I do not remember the name of my teacher, even though one of her classes is engraved in my memory as an extraordinary experience that affected me deeply. We were the second class to start our high school in the seventh grade before there were middle schools in Israel, we went through screening exams, and we were smart, at least in our own eyes and smugly knowledgeable. When the teacher said:  “We would learn today about the candle.” The class broke into laughter; it seemed childish and not “scientific” enough for us. I’m afraid I’ve been among the laughing. Pretty soon she asked why the wax was burning up the wick and not burning in the candle? At once, in a fraction of a second, as in a revelation, I understood three things:

  • First, that despite my laugher, I do not understand the candle burning at all.
  • Secondly, there is a fascinating science in the most trivial things around us, like candles I have known well from Chanukah ceremonies and Shabbat candles.
  • Third, I don’t ask questions, which If I were the young man I hope to be, I would ask.

That’s a lot for a single lesson. My chemistry teacher knew nothing about the internal storm  I went through, and after years when I became a teacher myself, I thought about this lesson and I was hoping that sometimes I get to my students even when I don’t necessarily know about it.

When I worked at the Davidson Institute, Dr. Oved Kedem, my friend, introduced me to a thin book:

Six lectures on “The Chemical History of a Candle” that Michael Faraday gave at the Royal Institute in London in 1848 as part of the tradition of Christmas lectures for young people.

Michael Faraday was an English scientist, one of the best experimentalists in the history of science with an unusual life story. He was born into a poor family in London and was forced to help support the family as an apprentice in a local bookbinder and bookseller shop at age fourteen. He acquired all his education by reading books that were in the shop. The beginning of his scientific career was in popular lectures by Sir Humphry Davy, the president of the Royal Society at the time, so that his Christmas lectures were closing a circle. You can find the original book here. Those who do not want to deal with the original text can watch the series of short films done by Bill Hammack to present and explain Michael Faraday’s lectures.

On the fourth page, Michael Faraday answers the question  of my chemistry teacher:

 “Then there is another point about these candles which will answer a question—that is, as to the way in which this fluid gets out of the cup, up the wick, and into the place of combustion. You know that the flames on these burning wicks in candles made of beeswax, stearin, or spermaceti, do not run down to the wax or other matter, and melt it all away, but keep to their own right place. They are fenced off from the fluid below, and do not encroach on the cup at the sides. I cannot imagine a more beautiful example than the condition of adjustment under which a candle makes one part subserve to the other to the very end of its action. A combustible thing like that, burning away gradually, never being intruded upon by the flame, is a very beautiful sight, especially when you come to learn what a vigorous thing flame is—what power it has of destroying the wax itself when it gets hold of it, and of disturbing its proper form if it come only too near.”

This booklet is a real gem, and I met it much more experienced, after completing three degrees in science, but I was still fascinated and surprised by the opening sentence  that opened the lectures, and I think that al-Jazari would be curious too:

“There is not a law under which any part of this universe is governed which does not come into play and is touched upon in these phenomena. There is no better, there is no more open door by which you can enter into the study of natural philosophy than by considering the physical phenomena of a candle.”

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The Scribe Candle clock, on clock face and hands

Introduction

The Scribe candle clock is the second scribe holding a pen out of three scribes that appear in the book. The scribe rotates continuously and passes fifteen degrees every hour, so one degree (one marking) is approximately four minutes. We already met a scribe holding a pen in the elephant water clock (in Hebrew), and soon I hope to write on the beaker water clock that has a different mechanism, but a very similar scribe. The scribe and his pen are used as a hand in a clock. It reminded me “modern” analog clocks and made me go back and examine the development of concepts such as minutes and seconds and the development of the clock dial.

The candle clock of the scribe ” Book of Knowledge of Ingenious Mechanical Devices” Topkapi manuscript, 1206.

How does it work?

Al-Jazari opens this chapter:

“I came upon a clock made by Yunus al-Asturlabi which had the appearance of the clock I described in the first chapter[ meaning the candle clock of the sword men]. A cross-beam which had a hole in its center for the wick replaced the cap which I used to hold the candle down, and I discovered that the wax flowed into the interior of the sheath and over the instruments inside the sheath. .. This gave much trouble; for this reason the design was useless. “

We do not know who Yunus al-Asturlabi was. Eilhard Wiedemann, a German physicist, one of the first researchers of science in Islam, who did much to bring the work of the al-Jazari to the west, suggested the astronomer and mathematician Ibn Yunus. Probably we will never know for sure. Correct identification or not, it is quite interesting because we have no evidence of any sophisticated candle clocks before al-Jazari’s.

The technical explanation, as always, will be colored in blue, so anyone who is not interested in pulleys or balancing weight can skip those bits. The drawing below is by the book translator and annotator Donald R. Hill with my captions:

A drawing of the mechanism by Donald Hill with my captions

The candle is placed on a holder inside a brass sheath, and only the wick protrudes through a hole in the cap. A long rod is soldered to the bottom of the holder. The rod runs through the main weight so that the weight is free to move up and down. Two strings are connected to the bottom of the rod and through two pulleys to the main weight. The latter is relatively heavy, slightly more than one kilogram. At nightfall the wick is lit, at that time the candle is in full size, the rod reaches its lowest point and the main weight its highest. As the candle is consumed, the main weight will descend exerting force, through the pulleys, on the holder upward and the holder and rod will go up at a constant rate depending on the rate of the combustion. A string which turns the scribe is attached to the bottom of the weight. Every hour the scribe and his pen will cover 150, so one can tell the time within 4 minutes. The holder pulls the ball’s channel up and every hour the highest ball in the channel has risen until it is level with the hole in the back of the falcon’s head, at which point it rolls out and falls from the falcon beak.

Minutes and their measurement

The globe and the clock face owe their divisions to a numerical system which is four thousand years old. The Babylonians made astronomical calculations using Sexagesimal (base 60) numeral system.  We can only conjecture why people of the ancient Middle East (Assyrians were also Sexagesimal ) adopted the use of base 60. One assumption is that the number 60 was chosen because it is the first number divisible by all the numbers 1 to 6. Alternatively, base 60 was preferred because the lunar year contains three hundred and sixty days. There are more suggestions. Hipparchus of Nicaea already mentioned here(Hebrew), as well as other Greek astronomers, used the tools previously developed by the Babylonians astronomers.  Hipparchus used the geometry of a sphere to find locations on Earth. There were attempts to use grid lines before, but he was the first to apply rigorous mathematical principles to the determination of places on the Earth’s surface, by specifying their longitude and latitude in terms of 3600 running South to North(longitude) and parallel to the equator(latitude).

Claudius Ptolemy considered the most famous astronomer of antiquity. His book the Almagest, from Arabic  (المجسطي) is considered to be one of the most influential scientific texts of all time. Its geocentric model whereby planets revolve around Earth was accepted for more than twelve hundred years until the work of Nicolaus Copernicus in the 16th century. Ptolemy used and expanded the work of Hipparchus by subdivisions of 3600 of longitude and latitude into smaller sections. Each degree was divided into sixty parts called “partes minutae primae” literally “the first small part.” This was later reduced to minutes. The minutes were further divided into sixty “partes minutae secundae” or “second small parts.” Later reduced to seconds.  Interestingly enough the time units in Hebrew “DAKA” and “SHNIYA” reflect the historical names.

Clock still didn’t show minutes and seconds for hundreds of years after the Almagest, partly because of technology limitations and partly because there was no need. In the middle ages, the meaning of an hour as sixty minutes was not understood by most people. Not many mechanical clocks from the fourteenth century are left, but those I could find do not have hands, in most cases, and ring a bell to indicate the hours.

The Salisbury cathedral clock is said to be the oldest working clock in the world. It is dated to 1386 (not certain). It is a large iron-framed clock without a dial and obviously with no hands. There are other clocks competing for this title. None of them has minutes’ hand:

The Salisbury cathedral clock

The Forchtenberg clock tower in a small town in south Germany is one of the oldest surviving mechanical clock towers. In contrast to the controversial dating of the Salisbury cathedral clock, the year 1463 is carved in iron. The only uncertainty; was the clock made at this date? Or could it be older and this is the first repair date? This clock has only an hour hand:

The Forchtenberg clock tower

Who was the first to install the minute hand? It is not clear, but the second hand has a story we know. Jost Bürgi was a Swiss clockmaker, a maker of astronomical instruments and a mathematician. He was employed at the Court William IV, Landgrave of Hesse-Kassel, a mathematician and astronomer by himself. Although now forgotten he was an outstanding astronomer, his observations, particularly those of the fixed stars, were at least as accurate as those by Tycho Brahe. Bürgi was brought to the court to develop scientific instruments, and assist in the observation that could confirm the heliocentric model by Copernicus. He built various instruments. In 14th April 1586, the count wrote to Tycho Brahe about a highly accurate clock which Bürgi had built which, for the first time, had a minute hand, a seconds hand and had an error of less than a minute in 24 hours! Christoph Rothman, another astronomer wrote about the new amazing clock:

“The duration of a second is not very short but resembles the length of the shortest note in a moderately slow song.“

This quote commemorates a time when science and technology produce a new reality.

Bürgi precision clock

Epilogue

I read today about a new exhibition of Christian Boltanski in the Israel Museum called “life”. He wrote: [my translation from Hebrew]

“a major part of my job is the fact that each person is special, one-of-a-kind and important, each will finally vanish. Most of us will be forgotten in two generations, with the passing of those close to us. “

It’s certainly not true for al-Jazari but probably true for most of us. The exhibition combines early works of Boltanski alongside new works and includes a digital timer continually counting the seconds from the moment of birth of the artist. I found a photo of a timer installation of Boltanski at the Biennale. I don’t know if the installation in the Israel Museum is identical.

Christian Boltanski, the Venice Art Biennale, 2011.