Zhang Heng seismometer distant earthquake direction

An ancient Chinese device could point toward a distant earthquake

400–500 km

In 132 CE, Zhang Heng built a device that could show the direction of an earthquake even when people nearby felt nothing. It once pointed northwest from the Chinese capital. A later message reported an earthquake about 400–500 kilometers away in that direction.

Medieval Islamic hospitals had wards, pharmacies, and patient records

Hospitals in the Islamic world developed separate wards, pharmacies, written patient records, and organized hygiene. Many of these features would still look familiar in a modern hospital. Medical books also helped carry some of this knowledge into Europe.

Pure water can stay liquid far below freezing

About −48.3 °C

Very pure water can remain liquid far below 0 °C if ice crystals have nowhere to start forming. Under carefully controlled conditions, liquid water can be supercooled to around −48 °C before it freezes spontaneously.

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Zhang Heng seismometer distant earthquake direction

An ancient Chinese device could point toward a distant earthquake

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