Inō, Tadataka

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Inō, Tadataka

(b. Ozekimura, Yamabegum, KazusanoKuni, Japan 11 February 1745; d. Kameshimachō, Hacchōbori Tokyo, Japan, 17 March 1818)

astronomy, surveying, cartography.

The son of Jinpo Rizeamon Sadatsune, Tadataka had an unhappy childhood. His mother died in 1751, and because his father and his stepmother could not support him he stayed with various relatives. It is believed that as a boy he studied mathematics and medicine.

In 1762 he married a girl four years his senior, the daughter of a wealthy landowner and brewer named Inō.(Since the Inōs had no son, he was adopted by them and took their surname.) The adopted Inō proved himself an able businessman, managing a brewery, buying and selling grain, and setting up a firewood warehouse in Tokyo. His wife died in 1784, and he remarried in 1790.

In 1794 Inō officially retired and the next year left for Edo (Tokyo), where he studied astronomy under Takahashi Yoshitoki, an official astronomer. His formal scientific studies began only at the age of fifty, and from then until the age of seventy-three, two years before his death, he worked energetically in astronomical surveying. (After his retirement Inō called himself Kageyu). At the time that Inō became Takahashi’s pupil, the Asada school was the most prominent in Japanese astronomy. Although Asada Gōryū himself was past his prime, his students Takahashi and Hazama Shigetomi were revising the calendar based upon such Sino-Jesuit works as Li- hsiang K’ao-ch’eng. In 1897 the Kansei revision of the calendar was completed.

A major astronomical and geodetic problem of the time in Japan was the finding of the length of a meridian by Japanese measure. Since Li-hsiang K’ao’eng had set zero longitude at Peking, that of Japan had to be accurately measured so that, in predicting a solar eclipse, the Sino-Jesuit method could be employed for the Japanese longitude.

In order to find the length of a meridian Inō volunteered to undertake a geodetic survey. Takahashi negotiated for him with the government, and in 1800 official permission for the survey was received. The Asada school was interested in the project from the point of view of astronomical geodesy, but the government permitted the private survey in hopes that it would contribute to the defense of northern Japan against possible Russian encroachments. The Russians had been active in the north since the end of the eighteenth century and the Japanese now wanted a coastal survey of Hokkaido, there being no satisfactory marine chart of that coast.

With several followers, Inō set out for Hokkaido via the northern part of the main island of Honshu. During the day they measured distances by number of steps (sometimes using a pedometer) and the bearings of distant mountains. At night, using a quadrant, they observed the altitude of a fixed star as it crossed the meridian. After compiling the results of their survey, Inō produced a map and presented it to the government. He subsequently conducted many successful surveys in northeastern Japan. His success aroused enthusiasm for surveying among many of his followers, especially Honds Rimei.

In 1804 Inō undertook a government project to survey the western seacoast of Japan. In comparison with the privately done, somewhat inexact survey of northeastern Japan, which had been carried out with insufficient personnel and funds, this better supported, government-sponsored survey of western Japan was very accurate and detailed; there was a larger budget, and personnel were also allowed various privileges on the site. After making over 2,000 measurements of latitude, Inō calculated the length of a meridian which agreed (within several tenths of a second of a degree) with the figure given in the Dutch translation of Lalande’s Astronomie (Amsterdam, 1775), which source Takahashi had obtained in 1803.

On Inōs maps zero longitude is through Kyoto. Inō tried to utilize celestial observation to measure longitude, as by noting, for instance, the solar and lunar eclipses from two different points and by observing an eclipse of a satellite of Jupiter. He had to revert, however, to fixing longitude by measuring distances along the earth’s surface. This procedure affected the accuracy of his maps, especially that of Hokkaido, in which there was a systematic error of several tenths of a minute.

Inō was an energetic field observer but did not excel in devising new methods or new theories in either astronomy or geodesy. While he was active, knowledge of Western astronomy was available through Dutch translations and Sino-Jesuit works and, later, through the works of Lalande; but Inō had no knowledge of Dutch or dynamics and little understanding of astronomical theories. When calculating the length of the meridian, he considered the earth as a perfect sphere rather than a spheroid. Moreover, when observing the positions of fixed stars, he did not take into account the effects of refraction, parallax, or nutation. In his surveying, Inō did not use modern triangulation but relied upon the old traverse method. His mapmaking approach resembled the Sanson-Flamsteed method (it is presumed that his method was developed independently), which is appropriate only for small areas; Inō nonetheless used the method for an area as large as all of Japan.

Despite Inō’s scientific failings, his map of Japan, based upon surveys covering the length and breadth of the land, has an important place in geographical history. George Sarton compares his contribution with that of Ferdinand Hassler, founder of the U.S. Coast and Geodetic Survey.

Historically, the only scientific technique used in Japanese mapmaking and surveying had been that of the plane survey, adopted from China in ancient times and used mainly for measuring fields. Astronomical observation had been restricted to city planning, and used for establishing the north-south axis of the checkerboard grid plans copied from the cities of the ancient Chinese dynasties. In the Middle Ages, when the influence of the Chinese civilization weakened and Japan was constantly engaged in internal wars, techniques of mapmaking and surveying improved somewhat, since they were necessary for military purposes in measuring terrain and laying out fortresses; but, judging from extant maps, these techniques were only good enough to make crude sketch maps.

In the sixteenth and seventeenth centuries Westerners came to Japan, bringing with them European surveying techniques and instruments such as the astrolabe; but after Japan virtually closed its doors to the outside world in the seventeenth century, it lost any direct contact with Western countries. The only surveying school, the Shimizu in Nagasaki, was secretive about its methods, which were never published in book form or developed much further. On the other hand, in the seventeenth century the world map of Matteo Ricci (in Sino-Jesuit works) was introduced, and in 1720 the ban on publication of nonChristian works in Western languages was lifted. Sino-Jesuit books on astronomy and surveying were increasingly studied. The first Japanese map showing latitude and longitude was published by Nagakubo Sekisui in 1779. This map, although it went through many revisions and was widely published, was deficient in interpreting the basically Wastern concept of longitude and latitude. (The first governmentappointed astronomer, Shibukawa Harumi, and his follower Tani Jinzan had tried in the seventeenth century to determine the latitude of various places, but their observation error was well over ten minutes of a degree.)

Hence Inō’s map of Japan was far superior to maps then in use, and to an amateur, his results look almost like modern maps. It was a revolutionary step forward. But since his map was produced by government order, it was not published or made available to the public; thus its influence was very limited.

In 1826 the German natural historian Philipp franz von Siebold came to Edo. Takahashi Kageyasu, the official astronomer of the time and a son of Takahashi, gave Inō’s map of Japan to Siebold in exchange for his maps and books. Knowledge of this reached the government in 1828, when Siebold was about to leave Japan. Takahashi Kageyasu was arrested and died in prison, and Siebold was subsequently deported. This incident amply illustrates the government’s treatment of Inō’s map as a top-secret document.

Because Inō’s brilliant work was not known to the reast of the world, the Europeans depended on a map produced in 1827 by a Russian admiral, Adam Johann von Krusenstern, which was clearly inferior to Inō’s Although the original of Inō’s map was confiscated, Siebold succeeded in smuggling out a copy. After revising it on the basis of the Mercator projection, hen published it in 1840 as Karte vom Japanischen Reiche. Since Inō’s map was not published in Japan, this revision was reimported to Japan, where it was copied.

Under the Edo Treaty of 1858, H. M. S. Acteon came to Japan in 1861 and asked the shogunate for permission to survey the coastline. In Japan xenophobia was at its peak, and the government thought it unsafe to grant the permission. Instead it gave the British a copy of Inō’s map. The British found the coastline described with sufficient accuracy for them to be satisfied with measuring only the depth of the surrounding seas.

After the Meiji Restoration, with the new government anxious to build a modern nation, an accurate map of Japan became a necessity for reasons both of prestige and of foreign trade. All the Japanese maps produced during the 1870’s and 1880’s by various government departments and the military were based on Inō’s pioneering map.


I. Original Works. Inō’s works consist mainly of maps, observations, recordsof his surveys, field notes, and diaries. Most of these are in the Inō’s Memorial Hall in Sahara. Among them there is a copybook entitled Bukkoku rekishōhen sekimō (1816 or 1817), a thesis strongly criticizing Entsū’s Bukkoku rekishōhen, 5 vols. (1810), in which Entsū disputed the Western astronomical cosmology, basing his rebuttal upon the Buddhist theory of Shumisen.

II. Secondary Literature. Ōtani Ryokicki, Inō Tadataka (Tokyo, 1917), which was published in commemoration of the centenary of Inō’s death, is the standard biography at present. It is an exhaustive critical study. There are many biographies of Inō, including some aiming for popularity, but all of them are either excerpts from Ōtani’s book or partial additions to it.

In commemoration of the 150th anniversary of Inō’s death, the Tokyo Geographical Scociety published many articles (in Japanese) on Inō in its Chigaku Zasshi. Many of them are partial amendments or additions to Ōtani’s book. Significant among them are"The Life of Tadataka Inō, the first Land Surveyor in the Yedo Period and his Contribution to the Modernization of Japan Since the Meiji Restoration,’76, no. 1 (1967), 1-21; ’Siugnificance and Essential Features of Inō’s Map in the History of Japanese Science and Cartorgraphy,”77, no.4 (19868), 193-222; Hoyanagi Mutsumi, ’British poreliminary Chart of Japan and Part of Korea Compiled From Inō’s Map,”79, no.4 (1970), 224-236; Masumura Hiroshi, ’Some Criticism on the Surverying Trips in ’Tadataka Inō’ Written by professor Ryokihi Ōtani,’ 77, no.1 (1968), 24-36; Nakamura Hiroshi,’Appreciation of Maps of Japan Made by Land Survery in the Edo Period Seen from the Standpoint of Cartographers is Europe and America,”78, no.1 (1969), 1-18; Akioka Takejiro, “Notes on some of Inō’s Maps Preserved in Japan,”76, no.6 (1967), 313-321; and Hirose Hideo, “On the Value of Longitude of Kyoto Appearing on Inōp’s Map Introduced to Eurpe by P. Siebold,”76, no.3 (1967), 150-153.

The publications in English are Ōtani Ryokichi, Tadataka Inō (Tokyo, 1932), rev. for foreign readers and trans. into English; George Sarton, in Isis, 26, no.1 (1936), 196-200, a comment on Ōtani’s book ; and W. G. Beasley,” An Undescribed Manuscript Copy of Inō Chukei’s Map in Japan,”in Geographical Journal, 117 (1951), 178-187.

On the history of cartography, see Fujita Motoharu, Japanese Geographical History, rev. ed.(Katanae, 1942); and Akioka Takejiro, History of Japanese Mapmaking (Kawaide, 1955), which evaluates Inō’s contribution to geographical history.

Shigeru Nakayama