Yulia Frumer’s Making Time: Astronomical Time Measurement in Tokugawa Japan will fascinate readers with its study of the evolution of different systems of time measurement in Japan. The book begins with the arrival of the first Western mechanical clocks during the Tokugawa (or Edo) period from 1603 to 1868, when the ruling shogunate restricted contact with foreigners and strengthened the country’s traditional temporal system. The author then traces timekeeping technologies and systems through to the calendar reform of 1873, when the Japanese people wholeheartedly embraced Western methods of timekeeping.

A pocket watch made for the Japanese market circa 1715.

A pocket watch made for the Japanese market circa 1715.

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In 17th-century Japan, Western clocks seemed nonsensical to consumers because they measured time in 24 equal hours and were dissociated from natural events like dawn and dusk. By contrast, the Japanese people divided their day into 12 unequal hours, following an ancient Chinese system introduced in Japan in the 7th century. Daylight and darkness were each split into six equal parts, no matter what the season. The daylight hours grew longer in the summer and shorter in the winter, with the reverse occurring for the nighttime hours. The hours of the day and night were equal in length only on the equinoxes. Each hour was named for 1 of 12 animal signs and was also given a number that could be used to announce the hour by strikes of a bell. Midday, for example, was Horse (9). A vestige of this system is still found in the modern Japanese expression that refers to morning as “before Horse” and afternoon as “after Horse.”

Although sundials could find the time directly from the Sun overhead, water and fire clocks were commonly used to keep time. Incense clocks, a type of fire clock widely used in the Tokugawa period, had moveable hour markers placed in the sand alongside a trail of burning incense and required a standardized system for shifting the hour markers as the year progressed. The lengths of day and night hours were adjusted 24 times a year according to seasonal weather changes such as with the “beginning of spring,” “rain water,” “major heat,” “cold dew,” “frost descending,” and “major snow.”

Japanese users noticed that those seasonal weather markers were not in tune with Japan but with northern China, where the calendar had originated. Moreover, scholars saw the need to regulate the lunar calendar against the solar year so that the seasons would not drift. To that end, the central government established an astronomical bureau to manage and reform the calendar as needed.

Frumer notes that by the late 17th century, Japan had in place a standardized calendar and a single time zone for the entire country. She also shows how Japanese clockmakers reengineered Western mechanical clocks to keep variable hours and shape them to suit Japanese life. Weights on the ends of the foliot in early mechanical clocks were shifted as often as twice daily to speed up or slow down the passage of day or night hours. Later mechanical clocks had moveable digits, index arms with adjustable lengths, and faces marked with hour lines like sundials.

Frumer argues that Tokugawa astronomers became comfortable with Western clocks and the system of 24 equal hours during the 18th century, as they measured the motion of heavenly bodies along celestial arcs and timed star transits. In the context of longitude determination, the author says, astronomers came to see time as a mathematical “belt” wrapping around the globe and the universe behaving more like an equal-hour timepiece than a variable clock of the early Tokugawa period. By the Meiji period, when Japanese society opened up to international commerce, Western timekeeping practices had become associated with positive values such as convenience, social progress, science, and enlightenment. The equal-hour system had another advantage for the Meiji government: It shifted people away from divination practices and superstitions linked to the unequal hours and their animal associations. Thus, in 1873 the Japanese government mandated the use of the 24-hour clock.

Making Time is the most comprehensive treatment of Japanese timekeeping to date, but it is not a specialized book for horologists interested in detailed information about clock mechanisms and makers. Frumer’s text is addressed to historians of science, technology, and Japanese culture. She deftly shows that technology is not just about practical needs; it is shaped by a society’s values and activities. Frumer’s book also prompts questions about technology transfer by showing how clocks from Europe that landed in Japan did not always have the same interpretation or use in their new environment. If the book has a shortcoming, it is that the narrow focus on timekeeping left me wishing for a broad history of Japanese methods of time finding and material culture. (I say this, admittedly, as the curator of a large collection of Japanese sundials.)

Time pluralism was also common in Europe during that time period, although Frumer doesn’t make the point. Not only were the Gregorian and Julian calendars in simultaneous use, but solar time was read according to multiple systems of equal hours, which varied by geographical region and type of work, and the Catholic church also employed some timekeeping methods that used unequal hours. European pocket sundials enabled users to track the time in different systems, find the lengths of day and night in different seasons, and compensate for diverse latitudes. Those sundials shared similar functions with the clocks and astronomical activities discussed in Frumer’s book, and their use was shaped by social needs in similar ways. That is not a criticism of the book; it is a note that Frumer’s analysis has reach far beyond Japan.

Sara J. Schechner is the David P. Wheatland Curator of the Harvard Collection of Historical Scientific Instruments and author of several books on the material culture of time measurement.