The Earliest Japanese Telescope Owned by Tokugawa Yoshinao

Abstract

Although historical records show that a telescope was first brought about into Japan as early as in 1613, existing telescopes in Japan produced before 1750 are rare and have never been examined in detail. In 2003 and 2005, we had a chance to scrutinize the antique telescope owned by one of feudal warlords, Tokugawa Yoshinao, who was the ninth son of the first Shogun Iyeyasu and inherited a large han (clan) at Owari-Nagoya district. Since Yoshinao died in 1650, it means that his telescope was made in or before that year. Our investigations of the telescope revealed that it is of Schyrlean type, namely, a more advanced one than the Galilean telescope, consisting of four convex lenses. In Europe, the invention of the Schyrlean telescope was publicized in 1645. Optical measurements showed that Yoshinao's telescope gave erect images with a measured magnifying power of 3.9 (+/- 0.2-0.3). The design, fabrication technique of the tube and caps of the telescope, and tube decoration all point to that it is neither a Western product at all nor a pure Japanese make. It is likely that the telescope was produced probably under the guidance of the Jesuit missionary in China or by the native Chinese, near cities of Suzhou or Hangzhou in Zhejiang province of the continental China, or at Nagasaki. Based on the Japanese and Chinese historical literature, we also discuss the possibility that production of the Schyrlean telescope could have begun independently in the Far East, nearly simultaneously with the invention of that type in Europe.