In 1849 Le Liancourt, a French whaling ship, ‘discovered’ the islands that are now referred to as “Takeshima.” Afterwards, Takeshima became known as the Liancourt Rocks. In 1787 French explorer Jean François de Galaup, comte de Lapérouse ‘discovered’ Utsuryo Island, naming it Dagelet Island. Then in 1789 English explorer James Colnett named Utsuryo as Argonaut Island. Both Dagelet and Argonaut were intended to refer to Utsuryo Island but were recorded at different coordinates and thus two different islands were indicated on Western maps. On the other hand, German physician and traveler Philipp Franz von Siebold, who had lived in Nagasaki’s Dejima quarter, published a map of Japan in 1840. Siebold had brought a Japanese map (Kaisei Nihon Yochi Rotei Zenzu, “A Revised Route Map of Japan” by Nagakubo Sekisui, a Japanese cartographer) back to the West. Nagakubo’s map of Japan indicated today’s Utsuryo Island as “Takeshima” and present-day Takeshima as “Matsushima.” As such, Siebold thought that Argonaut was Takeshima and Dagelet was Matsushima, and so indicated on his map. (Today’s Takeshima had not yet been ‘discovered’ by the West and was thus not indicated on Western maps.) Later, Argonaut Island would disappear from maps after it was discovered that there was no island present at the coordinates to which it was attributed. Consequently, Utsuryo Island which was called Takeshima in Japan (i.e. Dagelet Island in the West) would become referred to as “Matsushima.” This would lead to substantial confusion in the future in regards to the names of these islands. (Ref.1)

Ref. 1: China pilot (Sea route documents of the British Navy), 4th edition, 1864, Chapter 15, “The Sea of Japan”

Related documents
Kawakami Kenzo, A Historical-Geographical Study of Takeshima, Kokon Shoin, 1966