Linear thinking

Recently I think there have been a few more different ways of showing time. Here’s a picture of the clock-setting interface on an iPhone:


The illusion of a circular wheel rotating is very strong, particularly when you flick it up and down with your finger – it speeds up and slows down like a well-oiled bicycle wheel. But the display is effectively a digital clock that’s also a linear analog clock.

Measuring time as a point along a line is probably as old as angular time measurement, if not older. Early sundials from Egypt show the length of the sun’s shadow being measured on a simple graduated stick, although angular displays are also common in the ancient world. Through history the passage of time has also been marked by a change of water level, a decrease in height of a marked candle, or a change in length of a trail of slow burning incense.

A striking linear clock can be seen in Picadilly Circus tube station in London. A metal band travels from east to west over a fixed Mercator map of the world, showing the mean solar time for any location. The band itself is a 24 hour indicator, but if you think about it, it’s clear it has to be 48 hours long (since it has to go round the back of the map).


There are a number of software linear clocks around. Here’s an old one called Stripclock that I used to run on my Palm. (You can google for this but there’s no current url for the author, who might be called Fraser McCrossan) This was great because by tapping you could zoom in closer and closer onto the time display – either watch the seconds speed by or follow the imperceptible movement of the week or month.


And here’s a more recent Flash version of the idea. Not zoomable, but compelling in a different way:


(The live Flash version is at Unlike the iPhone controls, you don’t get the sense of any circularity in time. To the left – if you could scroll back far enough – is the formation of the universe; to the right, the heat death of the solar system…

Notice that this style of display has exactly the same ‘problem’ as circular analog clocks: it’s hard to show the various time units to any proportional scale. A second is as big as a minute, although they move to the left much faster. This is a great picture of time flowing like water under a bridge.

Seasonal greetings

This year you can track Santa’s progress using high tech Google-ry.

The following picture isn’t Google Earth – it’s more “Georgian Earth”. It’s in the George III collection in the London Science Museum.

globe dial

Best wishes for next year, and many more 24 hour dials!

The world as seen from Paris in 1800

In the Musée des arts et métiers in Paris you can see this clock, a Cadran Universel made by Janvier in 1800:


This has a fixed outer dial containing a series of towns and cities around the world, arranged according to their longitude. Paris is at the top at 0 degrees (and London has been squeezed in as small as possible just above it and to the right, not yet at 0 degrees longitude!).

This circular list of geographic locations gives an intriguing picture of the world as seen from Paris in 1800. I’ve put together a quick list of a few of the places mentioned, with the Paris-based and my estimates of the London-based longitudes, to see how many can be identified:


7.5 (5.5) Gibraltar ESPA – Gibraltar
15.0 (13.0) I Lancerote Can. – Lanzarote
22.5 (20.5) Hola ISLANDE – ?
30.0 (28.0) Thule T’AUST – Thule Islan (Morrell Island) in South Sandwich Islands
37.5 (35.5) Olinde Bresil – Olinda, Brazil
45.0 (43.0) Rio Janeiro Br
52.5 (50.5) Para ?? AM.
60.0 (58.0) I Burgeo – Bridgetown, Barbados
67.5 (65.5) C de la Reselution
75.0 (73.0) La Conception A M
82.5 (80.5) Fanal & Savanna
90.0 (88.0) N Orleans
97.5 (95.5) Vera-Cruz
105.0 (103.0) Zacalula ? Tamazula in Mexico?
112.5 (110.5) S Joseph CALIF – San Jose ?
120.0 (118.0) I. S. Paul
127.5 (125.5) C. Flatterie – Cape Flatterie, near Seattle
135.0 (133.0) I Pitcairn – Pitcairn Island
142.5 (140.5) I Cumberland
150.0 (148.0) I Milea . Ounab
157.5 (155.5) ? – obscured by the hands
165.0 (163.0) ? – obscured by the hands
172.5 (170.5) I de Navigateurs

Conspicuous by their absence are most of the major US cities. In 1800, these were either unimportant or deliberately ignored, apart from New Orleans and Savannah.

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.