Sangaku in Kyoto

When I knew we were going Japan before Taiwan,  I started reading one of my books that I had skimmed before: "Scared Mathematics - Japan Temple Geometry". This book describes a period of Japanese mathematics when Japan was isolated from the rest of the world. During the Tokugawa period, 1603 to 1868, there were mathematicians in the samurai class that developed their own brand of geometry. Starting with the Chinese mathematics from before 1600, the Japanese mathematicians developed a special set of geometry problems that are different from the what has been developed in the West. While in Europe the calculus was being discovered, the Japanese mathematician were posting their own problems in the Shinto and Buddhist temple.

These problems were posted on wooden plaques and hung in the eves of the temples. Like many other mathematicians, they credited their insight in solving these problems to the gods and the plaques were their way of thanking the gods. (Mathematicians are often suspect, so attributing your work to the gods is always a good strategy.) These plaques are called "ema" and there are many other subjects for ema. There might be more than a 1000 ema on mathematical problems still in Japan, some of them are in Kyoto. The mathematical ema are called sangaku.

At the first temple I looked for sangaku was at the Kasui Shrine

, although I found some ema, I didn't find the sangaku.

they were not hung in the shrine but in a storage building on the site.

The second temple I looked for them was the Kitano-tenmangu Shrine.

There I did find a famous sangaku.

Again it was in a storage area on the shrine site.

But the sangaku, ink on wood, was in bad shape, the problems couldn't be read but they are in the book I'm reading.

I'm now reading the book in earnest, and I have even more reasons to visit Japan again.