Adjustable Constant-Flow Siphon Diagram

What it is

This is an engraved diagram, labeled Fig. 5, from Hero of Alexandria's Pneumatica. It shows a cylindrical vessel with handles, a central tube with a valve, internal rods, a floating sphere, and a curved outlet tube.

Why it matters

This diagram illustrates Hero's interest in using mechanical devices to control the flow of liquids precisely. Such diagrams are central to understanding his work as an engineer who combined mathematics with practical mechanics.

Diagrams like this, copied and recopied through later manuscripts and printed editions, are how Hero's inventive ideas were passed down to later scientists and engineers.

Look closer

• What do the handles, valve and float suggest about how this device was meant to work?
• Why might precise control of liquid flow have mattered to ancient engineers?
• How might this diagram have changed as it was copied by hand over many centuries?