The Water Clock of the Boat, a Serpent or a Dragon?


The boat clock is a simpler version of the elephant clock. The scribe indicates the minutes passed and one Dragon (two in the elephant clock) swinging on its axis every half an hour. It looks like an early sketch for the elephant clock or a simpler version for beginners. Perhaps, for this reason, nobody wrote, or at least I haven’t found anything nor restorations or animations in contrast to the abundance for the elephant clock. The Dragon appears here in more detail and also has a drawing of his own but the text refers to it as a serpent just with legs and wings, it got me thinking about the biblical serpent and the story of the tree of the knowledge of good and evil. This post is dedicated to the serpent-dragon, and on this occasion, I also explain the balancing process which allows the dragon to go for a marvelous swing and return safely on his legs.

The Boat Clock, Topkapi manuscript, 1206.

How does the dragon make a flip and Lands on his feet?

The technical explanation, as always, will be colored in blue, so anyone who is not interested in submersible floats or torque and center of mass can skip those bits. In the water clock of the boat, like the elephant clock, the main mechanism is a sinking float, a float with a hole which sinks slowly during half an hour. After half an hour the float is full of water and begins to sink quickly and releases a ball that falls into the dragon’s mouth:

Drawing from the book, Topkapi manuscript, I tilted the dragon to visualize the swing and added the lead weights in his tail and the ball.

The dragon is made of a thin brass plate which was rolled to a pipe and hammered to form the shape of a dragon. The dimensions are not very detailed, but the Dragon’s tail forms a circular ring of four fingers, or 8 cm, diameter. The dragon head is hammered separately and soldered to the ring. The Dragon’s legs are holding an axle which is free to rotate. The ball I added does not appear in the original drawing, but is described in the text and weighs 30 dirhams (درهم), almost 100 grams. When it falls into the Dragon’s mouth, it generates a torque causing the dragon to flip. A torque or moment of force is the rotational equivalent of linear force. The torque is given by the cross product of the position vector (distance vector) and the force vector:

Some of the students I taught physics during the years struggle with cross products and especially with the moment of force. But we all know intuitively that it is easier to open the door by pushing it near the handle than push it near the hinges.(larger r =larger torque). Or when we struggle to remove the lug nuts of a flat wheel, we often use a wrench extension for the same reason – to generate a larger torque.

When the dragon’s head is downwards, the ball falls off, and the lead weight in his tail exert torque in the opposite direction and reset the Dragon position. My love M.  said that the dragon is like a roly-poly and of course she is correct. This is a round-bottomed toy, usually egg-shaped, that tends to right itself when pushed at an angle, and does this in a seeming contradiction to the force of gravity.

Drawing of a roly-poly

The bottom of the toy is made of a high-density material such as metal, and thus the center of mass is low relative to the height of the toy. This is very similar to the lead weights in the tail of the dragon. The ball falls into the Dragon’s mouth function as the finger pushing the toy over. In both cases, the low center of mass exerts a torque that reinstates the upright orientation.

Interestingly enough al-Jazari calls the lead “black lead” (الرصاص اسود) because in his time they called Tin “white lead”. Maybe in a future post, I will write more about the metallurgy of the 12th century.

A Serpent or a Dragon?

Serpentes (snakes) are an elongated, legless, carnivorous suborder of reptiles. They are characterized by the absence of limbs. Al-Jazari serpent has wings and legs making it a legendary creature or a Dragon. Dragons do not exist (sorry if I offended the fans of dragons) and respectively do not have a rigid biological definition. A dragon is a large, serpent-like mythological creature that appears in the folklore of many cultures around the world. Beliefs about dragons vary significantly by region, so horns wings and the number of legs vary a lot. All dragons have superpowers. We are more aware dragons capable of breathing fire in the western cultures but Bakunawa, a dragon from the Philippines, can swallow the moon, and the Vietnamese dragon can control the weather. It can be argued that the Dragon figure was influenced by various snakes, especially spitting cobras, bats (wings) and giant lizards and in the modern era extinct dinosaurs. In the Wikipedia entry of the “Elephant clock” appears this wonderful quote in the name of al-Jazari signifying his “multicultural mentality”:

  “The elephant represents the Indian and African cultures, the two dragons represent Chinese culture, the phoenix represents Persian culture, the water work represents Greek culture, and the turban represents Islamic culture.”

Al-Jazari didn’t write these lines. Such errors are amazing and funny and are one of the risks of a free-content encyclopedia relying on volunteers editors.

In contrast to the threatening figure of the Western Dragon, Chinese Dragon is a symbol of strength, integrity, and wisdom. The Chinese Dragon is depicted as a lizard-like creature without wings and four clawed feet and long tendril appended to each side of the snout. Al-Jazari’s Dragon is not very Chinese. However, at home, we have a facsimile edition of the Sarajevo Haggadah.” It’s Passover Haggadah written in Barcelona around 1350, and it is considered to be the oldest surviving Haggadah. The Haggadah is displayed at the National Museum of Bosnia and Herzegovina in Sarajevo, and this is the origin of its name. To my surprise, the Haggadah is packed with dragons. On top of this, in the 19th century in Paris, a small book was printed: – L’ornementation des Moyen-âge. This is a collection of illustration from medieval manuscripts and also includes many dragons. The dragons in all three books are very similar, the same general, lizard-like structure, the same animal head which is not completely defined, small wings and legs. If my rationality hadn’t so constrained me, I would be convinced that the three illustrators visited some mysterious zoo and made a drawing of the dragon that was held not far from the reptile room.

Right side dragons from Haggadah Sarajevo, in the center the Dragon of the Boat, Topkapi manuscript and to the left a dragon from L’ornementation des manuscrits au Moyen-âge

All this discussion about snakes with legs took me back to the Bible story, Genesis 2-3.  Adam and Eve were in the garden of Eden, where “And out of the ground made the Lord God to grow every tree that is pleasant to the sight, and good for food; the tree of life also in the midst of the garden, and the tree of knowledge of good and evil.” God allowed Adam and Eve to enjoy the fruits of the Garden except for the tree of knowledge, “for in the day that thou eatest thereof thou shalt surely die. Now the serpent was more subtil than any beast of the field which the Lord God had made” The Serpent Tempted Eve claiming “then your eyes shall be opened, and ye shall be as gods, knowing good and evil.” Therefore the snake lost its legs and got in trouble with men kind: “And the Lord God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life:

Genesis 2-3 King James Version

But did al-Jazari know the Biblical story about how the ancient serpent lost his feet?

Years ago I visited the Topkapi Museum in Istanbul, and near one of the swords there was a summary of the “The Binding הָעֲקֵידָה Ha-Aqedah” only, Ishmael (and not Isac) is the victim and the hero of the story. First, I thought there was a confusion, but this is of course just my ignorance. Eid al-Adha ( عيد الأضحى‎) ‘Feast of the Sacrifice’ is the second of two Islamic holidays celebrated worldwide each year. The sacrifice celebrated is the sacrifice Ibrahim (Abraham) our father, was asked by God to sacrifice his son Ismail (Ishmael) though the Qur’an does not name the son. In my eyes, both stories are equally heinous, and already as a child, I remember my inner resistance. Like the story of the Binding, the story of the garden of Eden in the Quran is completely different:

“And you, Adam, inhabit the Garden, you and your wife, and eat whatever you wish; but do not approach this tree, lest you become sinners.

But Satan whispered to them, to reveal to them their nakedness, which was invisible to them. He said, “Your Lord has only forbidden you this tree, lest you become angels, or become immortals.”

Quran, Surah 7 elevation, Translated by Talal Itani.

In the Quran, there is no tree of knowledge. The only tree mentioned by name is the Tree of Immortality ( شجرة الخلود Shajarat al-Kholoud ) The Serpent is not the seducer but the devil himself, and he is tempting Adam and Eve with eternal life. In Surah 2, The Heifer, appears Iblis (إبليس), which is another name for the devil in Islam. Eve, as a woman, is the main guilty in the original sin, both in Judaism and Christianity. In Islam Eve is Adams’ partner and clean from sin.  It is very unlikely that al-Jazari didn’t know the Serpent from the story of the creation and knew only the Quran version and the source of the legs and wings who can tell?


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