Measuring Time at the Science Museum

Science Museum clock faceTime moves at the same speed wherever you are, doesn’t it? Well, not if Einstein’s theory of relativity is right. And maybe not if you measure it differently. There’s a fascinating free exhibition at the Science Museum about the many ways in which we’ve measured time over the years, starting with hourglasses and sundials and moving on through the very first clocks to the digital world of the present day. And guess what? One of the things it explains is how in Japan they used to measure time in a totally different way.

The earliest methods of measuring time all seem to be about timing the length of sermons. That’s what these sandglasses were used for. (They’re not hourglasses because they don’t necessarily measure just hours). The ones on the right were made in Italy in the 1600’s and can measure out 15, 30, 45 and 60 minutes respectively.

Science museum sandglasses

If there was enough sunshine (not much use in London at the moment then), a sundial  would do the job. This rather jolly column sundial dates from the 1600’s. The dragon’s tail serves as the gnomon (the gnomon is the bit that casts the shadow to indicate the time).

Science museum sundial

The key thing with a sundial is to line it up with celestial north (not the same as true north so be careful if you’re putting up a sundial in your garden). That made portable sundials a tad challenging.

Enter the universal sundial, where you could rotate it towards the sun – like this one, made in 1745. It has a pinhole so that a spot of light falls on the disk and the gnomon then indicates the hours on a scale on the dial.

Science museum universal sundial

No, I don’t quite see how that works either, but one thing I’ve realised researching this post is that early clockmaking was a difficult and complex business, best left to mathematicians like Christiaan Huygens, who was the first to use a pendulum in making clocks in 1656, thus establishing the first constant timekeeping mechanism. This astrological clock was made in Augsburg around 1630 and had a pendulum added later.

Science museum pendulum clock

Unfortunately, Japan missed out on the pendulum. Mechanical clocks were introduced to Japan in the sixteenth century by Dutch merchants, but after that Japan closed itself off from contact with the west, so they continued to make clocks that were driven by weights, or very occasionally, by springs. This clock, from the 1800’s, was driven by weights.

Science museum weight-driven clock

But accuracy wasn’t their only problem, Telling the time in Japan was a complicated business because they divided their day into six hours of daylight and six hours of darkness, and the length of the hours varied according to the season. When days were longer in the summer, so were the daylight hours; when days were shorter in the winter, daylight hours became shorter too.  The hours were named after the signs of the zodiac – rabbit, dragon, snake, horse, goat, monkey, rooster, dog, pig, rat, ox, tiger.

Besides the zodiac signs, the hours were numbered backwards from 9 to 4 (1-3 were not used for religious reasons) running from noon to midnight (which was numbered 9 as the count started again) and from midnight to noon. This meant that dawn and dusk were both counted as the sixth hour.

The face of this clock, dating from the 1800s,  shows the zodiac signs around the outer dial and the numbering system running twice around the inner dial. It has two escapements in order to reflect the fact that day and night hours are of different lengths. (The escapement is the bit of the clock that transfers the force of the spring, weight or pendulum that drives the clock to the clock mechanism).

Science museum lantern clock face

That clock is a traditional lantern clock (it’s not clear why they were called lantern clocks – maybe from the shape which looked like a lantern).

Science museum lantern clock

But it was actually easier in the Japanese time system to measure time on a pillar type clock, where the time is shown by the height of the weight that drives the clock. You can see the horizontal bar pointer that tells the time in this pillar clock, dating from the 1800’s.

Science museum pillar clock

There were also other shapes of clock, like this table clock from the 1800’s, which has arabic numerals as well as the zodiac signs.

Science museum table clock

This frankly confusing clock, which comes with its own porcelain case, is driven by a spring attached to a cord which pulled the pointer along the linear dial. It has adjustable hour marks so you could change them according to the seasons.

Science museum linear clock

And sometimes people manipulated time for their own purposes – like the couple in this print by Isoda Koryusai from 1760-1780, where the woman is standing on her lover’s shoulders to reach the clock and slow it down to prolong their time together.

Isoda Koryusai c1760-1780

© Trustees of the British Museum

It must have been a relief all round when, in 1873 following the Meiji restoration and the opening up of Japan to the west, Japan adopted the western system of timekeeping.

P.S. With thanks to Yannick, my regular partner in crime, for taking me to see the clocks.

11 thoughts on “Measuring Time at the Science Museum

  1. Blimey – who knew telling the time could be so complicated?! Still, I like the idea of varying the length of an hour, making it longer when I’m enjoying myself – and vice versa. 😉


  2. Pingback: Giants’ Shoulders #60 Part II: The Present | The Renaissance Mathematicus

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