Relativity, Einstein

It's nostalgic to come up with geometry I did it in Mathematics III or C 

in Japanese education. I'm a little addicted to this book. 

The chapter using electromagnetism seems to be lost, but it’s attractive...

（Sorry for Japanese book link 📖）

It reminds me of Descartes' the Discourse on Method, 

but I wonder if that idea is valid in the age of data science.

I think it is valid as a way of thinking...