Steering the flow: a clock and a heart

This lesson asks you to describe what affects the flow of fluids, and to compare how fluids are used and their flow regulated in living things and in machines. The museum offers one machine, a water clock whose tank keeps its level, and one living system, the route of the blood through the heart and lungs. Factors such as the thickness of the fluid or the width of the pipe, and any measurement of flow, are for the class to investigate. ¹

The expectations ask for factors and for a comparison. For each of the two records, write what moves, what pushes or guides it, and what prevents it from going the wrong way.

Behind the display of the castle clock, a reservoir float descends with the water and transmits movement through ropes and pulleys ². A separate chamber has another float and a conical plug: when the water rises it closes the inlet, and when it falls it lets more in, so that the level stays approximately steady ³. One float provides motion through descent and the other regulates the feeding chamber, and a further regulator changes the position of the outlet for the required duration ⁴.

Ibn al-Nafis did not set out to write a book of his own: his aim was to explain Ibn Sina's anatomy, and when he reached the heart he departed from Ibn Sina and from Galen before him ⁵. For al-Jazari the records preserve no stated reason for the clock. They show how he worked: the author reports failed geometric divisions, then measures the water discharged in a fixed hour and sets the scale positions by calculation and experiment before engraving them ⁶.

West's article does not dispute that Ibn al-Nafis described the passage of blood through the lungs about three hundred years before anyone in Europe; the question it raises is whether Servetus and those after him knew his work ⁷. Servetus's words on the septum and the lungs resemble Ibn al-Nafis's, but a 1940 study by Owsei Temkin pointed out inconsistencies, and the 1547 Latin translation of another of his books apparently said nothing about it ⁷. West writes that many historians believe Servetus did not know the work; if so, both deserve credit, each in his own time ⁷.

In the castle clock, a float and a plug keep the tank at one level. In Ibn al-Nafis's account, a wall thicker than the rest of the heart stops the blood from crossing and sends it through the lung. Which of the two is a part that regulates how much flows, which one decides where it flows, and what in the records is your evidence?

• The castle clock: floats, a plug and an operator who resets the machine.
• The pulmonary circulation: the two routes of the blood, Galen's and Ibn al-Nafis's, side by side.
• Ibn al-Nafis: the physician, and what the records say of his life and works.
• Al-Jazari: the engineer, his patron and his book.

Read about the castle clock and the pulmonary circulation. Draw each as a line with arrows from where the fluid starts to where it ends, and mark every place where something steers it.