On the Value of Longitude of Kyoto Appeared on Ino's Map Introduced to Europe by Dr. Sieboldt

Abstract

A hand-written copy of one of Tadataka Ino's map of Japan was first introduced to European people by Dr. Ph. F. v. Sieboldt. Original Iro's maps showed only the differential longitude counted from the local prime meridian passing through the former site of the Institution of Calendar Reform at Nishi-Sanjo-Dai in Kyoto, but the very copy of Dr. Sieboldt was budged with the value 135°40′ as the value of the east longitude of the said prime meridian counted from Greenwich. In this paper, I have tried to explain how such value was obtained by Japanese astronomers.
After examining values of then existing or known values of the longitude of Japan, I arrived at the conclusion that the value 135°40′ was not those derived from Japanese astronomers' observations but deduced based on Captain A. J. Krusenstern's observations in Nagasaki and Tadataka Ino's land survey. The working value of the longitude of Kyoto adopted by Japanese astronomers of early nineteenth century was 135°55′45″, the value based on eclipse observations, and the value 135°40′ was never used for official astronomical purposes in Japan.