Wall sundial at Royal Square in St Helier, Jersey

Wall sundial at St Helier, Jersey

Wall sundial in Royal Square at St Helier, Jersey, Latitude 49.1839° N, Longitude 2.1057° W. The inscription reads: REGULATE YOUR CLOCKS BY THE SUN DIAL. CORRECTION MUST BE MADE FOR THE EQUATION OF TIME WHICH IS GIVEN IN ALL THE ALMANACKS.

This beautiful sundial is set into the wall of the old Picket House in Royal Square, St Helier, Jersey. Historical records show it was made by a talented Jerseyman called Elias Le Gros in the 1820s. In spite of being plastered over at one time by the military authorities and then restored again in 1875 after a public outcry over the dial’s obliteration, it is now in excellent condition, as our photo shows. Our host for lunch that day told us: “The dial is much admired but of course it isn’t accurate.” Poor old Elias Le Gros, now was the time to rescue his reputation!

The reference to the Equation of Time (EoT) below the dial clearly tells us Elias Le Gros knew his business. In the 1820s everyone who came to set their clocks by the dial would understand his meaning. It is only nowadays, when our clocks run by Greenwich Mean Time (GMT), or British Summer Time (BST), and of course by time on the Internet, we find sundials very confusing.

Our calculations show the Royal Square sundial is admirably accurate, correct to four minutes. Solar time reading on the sundial is XI plus 3 minutes i.e. 11.03 am. The camera data for our photo are Time 12:17 and Date 19 June 2023. The sundial is one hour and 14 minutes slow by the clock. This is only four minutes different from our solar time calculation, which is 1h 10m, EoT (1m 19s), BST (1 hour), and Longitude (8m 25s) all slow.