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Primary sourceBook

On Water Clocks

Hero of Alexandria

A fragment of Hero of Alexandria's Greek treatise on water clocks, describing how water-driven devices can be used to measure time.

This treatise is attributed to Hero himself, showing his direct work on measuring time with water-driven devices.

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Source: Wikisource

About this source

What it is

This is a surviving fragment, in its original Greek, of a treatise On Water Clocks attributed to Hero of Alexandria. It explains how a container with a small hole lets water flow out steadily, like a clepsydra, so that the amount of water that flows can be used to measure time.

Why it matters

Water clocks were an important technology in the ancient world, used to track hours when sundials could not (such as at night). This text shows Hero working as both a mathematician and a practical engineer, applying careful reasoning about ratios and proportion to a real mechanical device.

Look closer

  • What problem is Hero trying to solve with this device?
  • How does he use the idea of proportion ('as water to water, so time to time') to make his argument?
  • Why might measuring time accurately have mattered in the ancient world?

This book is part of the curated material that grounds the AI version of Hero of Alexandria on Humy.ai — when students ask about related events, the AI can quote it and cite it.

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