The clock of the doors and the Jewish question


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.

The pump and the Crankshaft


The fourth machine for raising water is a pump based on a slider-crank mechanism. A more detailed explanation about crank, its history, and why is it interesting will follow. Since the drawing by al-Jazari is difficult to understand, I will present the revised drawing by Dr. Donald R. Hill, The book translator, and annotator. This is a good opportunity to write a few words about Hill, who was instrumental in bringing this book to us and in understanding al-Jazari and his importance to the history of Engineering.

Machine for raising water from a pool, Chester Beatty Library in Dublin probably 15th century from Iran or Iraq

Donald Rutledge Hill (1922-1994)

Hill was born in London. He joined the English army engineering unit during World War II until he was wounded in action in Italy. Back in England, he studied Engineering at the London University, obtaining his engineering degree in1949. He later worked for the Iraq Petroleum Company in Lebanon, Syria, and Qatar. Hill was gifted in languages, and before arriving at the Middle East, he was already fluent in French, German, Spanish and Italian. The move allowed him to add spoken Arabic but also to master literary Arabic. In 1964 he completed an M.Litt in the history of Islam and 1970 a Ph.D. from the University of London. His impressive accomplishments are a result of the unique combination of engineering knowledge and mastery of Arabic as well as Orientalism at its best, the study of the Arabic culture rather than a romantic perception or in contrast to the West. His main contributions are the translations of “The Book of Knowledge of Ingenious Mechanical Devices,” by al-Jazari, which is the sole purpose of this blog. He also translated the “Banu Musa” mentioned here more than once, and “On the Construction of Water Clocks” attributed to Archimedes. His contribution far exceeds the traditional role of a translator and includes annotations, drawings and writing several books on the history of engineering and technology that helped reinstate the technology in the golden age of Islam to its proper place.

How does it work?

The technical explanation, as always, will be colored in blue, so anyone who is not interested in Cranks (Are you series? Without Cranks we would not have locomotives or cars!) Or toothed wheels can skip those bits

An ox, in the upper room, is rotating the system. If you are confused after the fake cow, in the previous post, this is an actual animal, and without it, the pump would not work. The part of the gears and the conversion of the rotary movement to a linear one is difficult to understand (for me and others), and it looks like al-Jazari drawing is in error. I bring side by side the original illustration by al-Jazari and the drawing by Hill, and I added captions.

Combined drawing, al-Jazari, and Hill

The Ox, in the top room, rotates the horizontal tooth-wheel, which in turn rotates a vertical tooth-wheel, much like the classic sāqīya already explained here. The difference is that the vertical tooth wheel is attached to a slider-crank. We met this mechanism in the water wheel pump where it converted circular motion to linear motion and possibly vice versa. This is an essential component in engines and pumps till this very day. This is an animation of the pump, and you can see the slider-crank mechanism clearly:

It is easy to see that when the wheel rotates the crank moves within the slot and since the ladle is anchored at the axle it will raise the water and empty them later. In al-Jazari drawing( in contrast to the text which is quite clear) it seems that the vertical tooth-wheel is in 900 and the crank is in an odd angle relative to the slot. Hill’s drawing is correcting all these problems and explains well how it worked. Large engines are usually multicylinder to reduce pulsations from individual firing strokes, with more than one piston attached to a complex crankshaft:

Flat-plane crankshaft (red), pistons (gray) in their cylinders (blue), and flywheel (black)


Many internet sites consider the crank as an invention of al-Jazari, for example here:

“In 1206, al-Jazari invented an early crankshaft, which he incorporated with a crank-connecting rod mechanism in his twin-cylinder pump. Like the modern crankshaft, al-Jazari’s device consisted of a wheel setting several crankpins into motion, with the wheel’s motion being circular and the pins moving back-and-forth in a straight line. The crankshaft described by al-Jazari transforms continuous rotary motion into linear reciprocating motion and is central to modern types of machinery such as the steam engine, internal combustion engine, and automatic controls. “

Before I expand a little on the evolution of the crank, it is important to note that the concept of an individual inventor is, in most cases, excessive romanticizing. It is inordinate when we have a definite inventor and more so for the Middle Ages or before that.  Take, for example, James Watt, who invented the steam engine in 1769 and issued a patent for it. A few children’s books suggest the idea of the steam engine came at the age of 12 while young James sat in the kitchen with his aunt, staring at a teakettle. The water was boiling so hard that the lid of the tea kettle began to jump up and down. This is simply not true. Watt invented the steam engine while fixing Newcomen’s steam engine for the University of Glasgow. This engine was invented in 1712 and was considered a great success. More than 100 such engines were installed as water pumps in mines in England and Wales. Also, the Newcomen engine is not the first steam engine, and there are predecessors from the 16th and 17th centuries. Don’t get me wrong, James Watt is entirely worthy of his glory, his improvements (the separate steam condenser and later the double-action engine) were very significant and the industrial revolution, for better or worse, is the consequence of the improvements by Watt.

The electric light bulb was invented by Edison, and the airplane was invented by the Wright brothers, but their story is not very different from the story of James Watt. Without diminishing their impotent contributions, their inventions, just like Watt’s steam engine, are a link in a long chain.

Manual cranks appeared in China during the Han dynasty (202 BC-220 AD), and we find ceramic models in the tombs of the period. However, the potential of the crank of converting circular motion into reciprocal motion never seems to have been fully realized in China. There are manual cranks examples from Europe and the Middle East. For example this picture of Roman iron crank for an unknown purpose from the 2nd century AD

roman crank

A Roman iron crank dating to the 2nd century AD was excavated in Augusta Raurica, Switzerland.

The crank appears in the book by the Banu Musa from the 9th century, which al-Jazari new and quoted. However, in their version, the crank did only a partial rotation which wouldn’t allow for significant power transfer.  Al-Jazari did not write, as he did in his fountain [in Hebrew], for example, that he looked at design by the Banu Musa and decided that it requires improvement and does not refer to the originality of his design.


Steam Engine, Wikipedia