Mitsuyoshi Yoshida

A mathematician from the early Edo period. Commonly known as Shichibei, his pen name was Kyuan. He was a member of the Suminokura clan in Saga, Kyoto, and Suminokura Ryoi was Mitsuyoshi's maternal grandfather. Mitsuyoshi loved mathematics from an early age, and studied it under Mori Shigeyoshi. Around this time, he obtained a Chinese abacus book, Sanpo Toso, and asked Shigeyoshi to teach him how to read it, but Shigeyoshi was unable to read it well enough. He was therefore taught by his maternal uncle, Suminokura Soan, and was able to understand it.

Mitsuyoshi wrote Jingoki (1627) using Sanpo Toso as a model. Reflecting Mitsuyoshi's environment, the contents of this book are largely aimed at wealthy townspeople. As his fame grew, he was invited by various feudal lords, but due to eye disease he did not enter their service. For a time he became a guest of Hosokawa Tadatoshi in Higo (Kumamoto prefecture), but after Tadatoshi's death he returned to Kyoto. In his later years he became blind and took refuge in the home of Soan's son, Gentsu. In addition to Jingoki, his other works include Wakanhennengounzu (revised version of Shaku Enchi's work, 1645) and Koreki Benran (Koreki Benran) (1648).

[Shinichi Oya]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

江戸時代初期の数学者。通称七兵衛、号は久庵。京都嵯峨(さが)の角倉(すみのくら)の一族で、角倉了以(りょうい)は光由の外祖父にあたる。光由は幼時から数学を好み、毛利重能(しげよし)について数学を学んだ。このころ、中国のそろばん書『算法統宗(さんぽうとうそう)』を入手、重能にこの書による教授を頼んだが、重能は十分読むことができなかった。そのため外伯父の角倉素庵(そあん)に教授を受け、これを理解した。

　この『算法統宗』を手本にして著述したのが『塵劫記(じんごうき)』（1627）である。この書は光由の環境を反映して、内容は富裕な町人を対象としたものが多い。その名が高くなるにつれて諸大名から招かれたが、眼疾のために仕官はせず、一時、肥後（熊本県）の細川忠利(ただとし)の客分となったが、忠利死後は京都に戻った。晩年は盲目となり、素庵の子玄通の家に身を寄せた。著書に、『塵劫記』のほか、『和漢編年合運図』（釈円智の著に手を加えたもの。1645）、『古暦便覧』（1648）がある。

［大矢真一］

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