Chasing the sun across the floor to tell the time

Merlin has always had an interest in time and time-keeping, and his study is home to five clocks (six if one counts the barograph). He always keeps his watch accurate to the second by using the famous six pips of the Greenwich Time Signal, which was first broadcast on the BBC Home Service (now Radio Four) in 1924.

Good clocks, able to keep time reliably, have been widely available for some 200 years. However, to set the time correctly on any clock requires some other means of obtaining the current time accurately and this has not always been easy. A sundial is the obvious solution, but most small sundials do not give the degree of precision required.

To solve this problem, meridian dials were sometimes employed. These consisted of a fine line, usually on the wall or floor of a room, and a shutter by a window with a small aperture in it. The line was orientated to point due north/south and the aperture positioned such that at local solar noon, the small patch of sunlight passing through it would cross the line.

Although meridian dials can be found in many cathedrals throughout Europe, few have survived in England. Merlin is aware of only four.

One of these meridian dials can be seen in the cloisters of Durham Cathedral. Another is at Bramshill House in Hampshire, but it is inaccessible to the public because the house is now part of the national police training college.

A third meridian dial can be seen in Kent. The Ramsgate Maritime Museum is in the Clock House on the quayside in Ramsgate harbour, where the Ramsgate Meridian is situated. The museum proudly states that local time is five minutes and 41 seconds ahead of Greenwich Mean Time.

The fourth meridian dial is in Nottingham, at Bromley House, the home of the Nottingham Subscription Library. The Nottingham meridian dial consists of a brass strip, with a fine line engraved on it, which was laid down in about 1834 across the floor of one of the first-floor rooms.

A shutter by the window has the necessary aperture and on sunny days members of the library sometimes gather to observe the transit of the spot of sunlight across the meridian at local solar noon. The latter is four minutes and 33 seconds behind Greenwich Mean Time.

Since this room, known as the Standfast Room, is also the library’s tea and coffee room, the occasion is a sociable one.