Revolutions in time

If you’re visiting Paris, a good place to see some interesting clocks is the Musée des arts et métiers.

In 1793, the Revolutionary Government in France decreed that the day should be divided into 10 hours of 100 minutes, and the year into 10 months of 30 days. For a few years, clock and watch makers designed some unusual pieces to help the population learn and adopt to the new decimal time system. Here’s a good example:


The single long hand with a circle at one end and a point at the other probably shows the hours in both old and new systems. One end points to the decimal time, with 10 (0) being midnight, and 5 being midday, the other end to the equivalent old-style time. Presumably, therefore, old-style midnight (XII) is at the bottom of the dial, so that the other end can point to 10 (0). 1 o’clock (decimal) is about 02:20 old style, and the position of the hour hand in this photograph suggests that the time is 0.90 (d), or 02:10 old style.

If the other brass hand is the new minute hand, it shows 80 decimal minutes past 0. In theory a time of 0.80 (d) corresponds with about 01:55, so perhaps the hands are not quite adjusted correctly – or my assumptions are incorrect.

The grey pointer indicates the calendar day – the 12th. Every day in the new Revolutionary calendar had a object or plant associated with it, so if the current month had been Pluviôse (Jan 20 ~ Feb 18), today would be Broccoli day. (For a full list, see here.)

Here’s a watch with, I expect, midnight at the bottom:


At about 3 o’clock (decimal), or 07:15, it’s time for croissants and café. Again it’s not clear whether the minute hand is showing old or new minutes.

This next example is more radical. Only half the dial is organized for the new decimal time, the other half is defiantly quadrovigesimal (duodecimal times two):  Presumably the long dual-purpose hour hand is used again here, but I’m puzzled as to why only the roman numerals I to V are used – converting to a new time format is hard enough without having to add 5 to the hour after midday. The shorter hand pointing to the 12 might be another old-style hour hand (how could it work?), but the other hand pointing to the 2 could be an old or new style minute hand. Some more research is needed.


Intriguingly, the museum shows only 10% of its holdings at a time, with the remaining items held in a big storage facility on the outskirts of Paris.

If you can’t get to this great museum in person – to see these and other wonderful scientific objects from the past (and to eat in the excellent cafe) – the museum’s web site is worth a look.


Atomic clocks

My Norwegian correspondent Tommy Toverud sent me some interesting links, including these to the Museum of Time and Frequency. This has a strange retro-feel to it – ‘atomic clock’ still sounds modern to me – but these are cool old new things.

I’ve borrowed a picture from the site. This is a picture of a General Radio Syncronometer model 1103-A

.general radio sychronometer

And this collection of Soviet space clocks is quite impressive.

Greenwich time

This screensaver is a reasonably accurate simulation of the famous Shepherd clock at Greenwich in London. If you have a Mac, you can download it from this site. See the Software page on this site, or download it from this link.


In 1852 Charles Shepherd installed a new clock outside the gate of the Royal Observatory at Greenwich. This was an electrically operated clock, one of the earliest ever made, and it was controlled by a master clock mechanism inside the main building.

While Shepherd provided the engineering know-how, the original idea had come from the Astronomer Royal, George Airy. With the arrival of the railway network, England had recently found that a single time standard was needed to replace the various incompatible local times then in use across the country. Airy decided that this standard time would be provided by the Royal Observatory. His idea was to use what he called ‘galvanism’ or electric signalling to transmit time pulses from Greenwich to slave clocks throughout the country. The new submarine cable recently installed between Dover to Calais in 1851 raised the possibility of sending time signals almost instantly between England and France – this would allow longitude differences to be measured very accurately, for the first time.

In September 1851, Airy wrote to Shepherd asking for proposals and estimates. He included a request for the following clocks:

One automatic clock. One clock with large dial to be seen by the Public, near the Observatory entrance, and three smaller clocks, all to be moved sympathetically with the automatic clock.

He also wanted the Greenwich time ball to be electrically operated, so that it would drop down its flagpole at exactly 13:00.

By August 1852, Shepherd had built and installed the network of clocks and cables in the observatory, although the costs were considerably higher than the original estimates. Shortly after, for the first time, Greenwich mean time was transmitted along cables from Greenwich to London Bridge, and thence to clocks and receivers throughout England. The primary pulse originated from this unlikely-looking master clock in the observatory.


By 1866, time signals were sent from this clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable.

The public clock at the gate originally indicated astronomical time, in which the counting of the 24 hours of a day started at noon every day rather than midnight.

This photograph was taken in the 1870s, and shows the clock approaching midday, at the astronomical time of 23:20.


A similar photograph, from 1870, shows the clock early in the morning, with the dial showing 18:52. The clock faces east, and the sun is high up to the north east (early morning). Obviously at midday astronomers can precisely observe the sun crossing the meridian so as to set or reset a clock. The 0 here means “start counting again”.


Following the International Meridian Conference, the clock was altered to show civil time with effect from 1 January 1885. Ever since, it’s shown Greenwich Mean Time, rather than British Summer Time (Daylight Saving Time).

The dial has seen numerous minor design changes over the years:

The original:

After a (not very successful) 1910 repainting:
after 1910 repainting

In 1940, a bomb destroyed the gates and damaged the dial. In 1947 a new replacement dial was installed:


The 1981 repainting thankfully reverted to an exact copy of the original design:


The clock is still ticking happily away today, although it’s now controlled by a quartz mechanism inside the main building. Here’s one of thousands of recent photographs:


The master clocks are still on display, as are the famous series of chronometers made by John Harrison. In the shop you can buy postcards and lapel pins of the clock (but no fridge magnets!) and there’s also a small 24 hour quartz clock on sale. It’s like a replica, although the complexities of the original Shepherd design have been replaced by a simpler interpretation.

When attempting my own version of this clock, the hardest parts were definitely the roman numerals. I couldn’t find any font which matched and had to draw them again from scratch. If you compare my copy and the original you’ll notice how much better the original is. Many subtle variations in size and placement were employed to produce an acceptable solution to an intractable problem: how to make numbers of such different widths do the same job. It’s not a pretty design, I have to say, but it has a good solid Victorian heaviness to it, which matches its history well.

For even more information about the clock, refer to this article on the Royal Observatory Greenwich website.

FESTO Harmonices Mundi

In the technology center of the Festo Company in Esslingen, Germany, you can see the amazing FESTO Harmonices Mundi.



From their web site:

Festo’s Technology Centre features an attraction of a symbolic nature, namely the Harmonices Mundi. This technical work of art consists of three parts – a world time clock, an astronomical clock and a glockenspiel – embodying the company’s innovative power and precision work.The Harmonices Mundi combines astronomy, mechanics, melodics and electronics. The name is based on a book of the same name written by Johannes Kepler in 1619. In this book, Kepler defines the laws that describe the structure of our planetary system. Fascinated by historical astronomy, Prof. Hans Scheurenbrand (a former member of the Managing Board) spent years working in his leisure time constructing the Harmonices Mundi for Festo.The three-part Harmonices Mundi also includes a modern glockenspiel, with 76 bells and 40 claves that can be struck to obtain various levels of sound.

With this clock the Professor is merging two cultures. The medieval desire to construct an analog simulation of the universe in clockwork, seen in many of the classic old astronomical clocks of the last 500 years, meets the modern obsession with visibility, documentation, and machine-like precision of design and manufacture. Every aspect of the clock’s construction has been meticulously described and illustrated (you can buy the book). You can also browse through this PDF (also in German), for more illustrations and a feel for the mathematical precision that’s going on behind the scenes.

The superb visual design of the project can be further explored on the web site of Linden-based agency Hild Design who worked on the graphics and typography. And you’ll also find an extract from Novum magazine on their site with some more luscious graphics.

It’s not obvious to me whether you can visit this clock if you’re passing through Esslingen, Germany. Perhaps someone can find out?

Thanks to Tommy for passing this on.

St Mark’s Venice

This weekend, the restored clock in St Mark’s Venice was unveiled.

st marks venice clock

The clock was first installed 500 years ago, and has seen many changes and restorations in its time. In the 1850s an illuminated digital display was added for telling the time at night.

You can read more about this clock, and the controversial restoration, in English (grazie!) at Orologeria.

Venice clock Cpo St Apostopoli

Thanks to David Evans for this picture. He writes:

I discovered this clock in Cpo SS Apostoli in Venice (between Ca D’Oro and Rialto Bridge. Can anyone explain how you use it?


The vagaries of medieval and renaissance Italian time-keeping are mentioned elsewhere on the site. My understanding is that the Italians started their counting from 1 at twilight or sunset, and counted all the way through the night, reaching 24 just before sunset (if things went like clockwork).

I don’t know whether ‘the authorities’ run any of their surviving clocks on the original schedules, maintaining the authentic ‘Italian hours’, for the benefit of tourists and the inconvenience of the residents. The central pointer is similar to the other Venice clock, although perhaps less easy to read. To my eyes, this clock says about 6. It’s obviously not midnight or 6 hours after sunset, so I think we can dismiss the ‘Italian hours’ idea. If the picture was taken at 6 or 7 in the morning (allowing for Daylight Saving Time), then the clock might either be working really well, or it’s broken, the photographer was lucky enough to be there at the one time of day when the clock was reading the right time.

More likely, though, the clock is either not working or not keeping the right time. You’ll have to go back and do some more research, David!