Many websites and popular science books explain the coloring of the rainbow. Though I have not checked all of them even in Japanese, I could not find a better explanation than that written by Ukichiro Nakaya in 1947. He wrote a science essay entitled “Niji” as a contribution to the first number of a science magazine “Niji” for young Japanese.  “Niji” is a rainbow in Japanese.

Nakaya died more than 50 years before, and his author’s copyright has vanished in Japan. You can find his essays in Aozora Bunko. Here, I place my translation of “Niji”. I know my English writing is terrible, and I hope someone will revise this translation to better English.