Joseon rain gauge
Why did people start measuring rain?
That time, that place
Joseon Korea under King Sejong. Farming was the foundation of the state, and tax was assessed on each year's harvest — which depended on rain. To adjust taxes and send relief, the court had to know how much rain had fallen where.
Why this question
The old method was to dig after the rain and measure how deep the soil was wet. But sand and clay drink water differently.
The same rainfall yields different numbers in different districts — and then you cannot tell which district suffered more. Numbers you cannot compare are worth nothing.
What was found
The answer was to take the soil out of it. Identical metal vessels were distributed nationwide, and the depth of water collected in them was measured with a graduated rule. If the vessel is the same, any two readings can be set side by side.
What mattered was not the vessel but the system built around it: a fixed specification, fixed times and methods of reading, and required reporting upward — from local districts to provincial offices to the astronomical bureau in the capital.
This was not one observation. It was observing an entire country at once.
Rainfall was estimated from how deep the ground was wet
Standardized gauges, and the reports from across the country preserved in the annals
Standardized rainfall networks appear in Europe only from the seventeenth century