In La Ciotat, on the port, there is a nice sundial:
It is an equatorial sundial, dating from 1873 called the barometer sundial, because it includes a barometer.
Like most sundials, it shows solar time, which is not the same as the time on our watches (standard time).
To enable it to be used for telling the (standard) time nonetheless, it is accompanied by two tables showing the difference between solar time and standard time for certain days of the year (three times a month: the 1st, the 10th and the 20th):
These tables give rise to two observations:
1. Summer and winter hours (in the plural)
Nowadays, we would tend to refer to summer (or winter) hour [in French “time” is hour, in this sense] in the singular. But more importantly, we note that each of these tables includes every month of the year. Yet it is hard to see how January could be a summer month, or July a winter month…
So why these unnecessary engravings?
We do not know for sure, but we venture two hypotheses (not exclusive):
Concern for symmetry: thus the two tables are the same size, which is more aesthetically pleasing?
Inability to know the date of the change in advance: it was not until the 1970s that the dates for switching to summer time or winter time were firmly established: the last Sunday in March and the last Sunday in October, respectively.
When daylight saving time was first introduced, the dates could vary from year to year. The engraver could not therefore know for certain in advance when the change would take place. Did he therefore include everything as a precaution?
2. These tables are incorrect!
Now, let’s check these tables.
For example, let’s take March, 1st.
Let’s use a Papophoplon set to the longitude of La Ciotat (which is given by the winter time table): 5°36’23″ east of Greenwich.
Converting this to decimal degrees gives 5.6°.
We find that we need to add 49 minutes and 53 seconds. As the dial table gives times in minutes, we’ll round it up to 50 minutes.
However, the sign says we need to subtract 9 minutes.
That’s nonsense!
Let’s try it out in summer. Let’s take August, 1st. The table tells us to add 44 minutes. The Papophoplon:
The Papophoplon says you need to add 1 hour and 44 minutes.
Did you get it?
That’s right, the tables are not based on today’s French time, but on the time used before the Second World War, when France was on Greenwich Mean Time.
So the error is correct: you need to add 1 hour to the times in the table:
Date | Table | Papophoplon | Écart |
March 1st | -9 minutes | +50 minutes | +59 minutes |
August 1st | +44 minutes | + 1h et 44 minutes | +60 minutes |
Conclusion 1
We can date these inscriptions: they must date from the 1920s or 1930s.
Indeed, they were made after the introduction of summer time in France, which dates back to 1917.
And they predate the early 1940s, when France switched to ‘German time’, i.e. GMT+1.
Conclusion 2
In both summer and winter, this sundial has been an hour out of sync for over 80 years.
Why isn’t there a crowd of people standing in front of this sundial, scratching their heads and saying it “doesn’t work”?
Our hypothesis: because nobody reads the tables accompanying sundials.
Our conclusion: tables need to be replaced with Papophoplons!
To find out more about this sundial
The sundial was renovated in 2023.
Michel Lalos’s website features photos of it before the renovation: here.
It is listed in the inventory of sundials maintained by the Commission des Cadrans Solaires (CCS) of the Société Astronomique de France (SAF) under the numbers (SAF inv.: 13028001-03 and SAF inv.: 13028001-04) for the summer and winter faces, respectively.