Year 2003

Sundial of the month January

The unique Jacobi Church mini-monument

The oldest dated polar style public sundial in The Netherlands

Utrecht

Before restoration

You would easily miss it, walking past. This sundial is beside the small south gate of the church.

The hour lines and Gothic numerals are chiseled in a slab of red-brown sand stone. The hours run from VI to XII, then up to VI.
After a moment's puzzle, we find the year 1463 within the inner circle. Mason's marks are bottom left and right.
Fitted in the centre of the circle is a copper rod (the style), which points towards the celestial pole. The shadow of the style indicates the time.
You may notice that the west side of this sundial lies somewhat deeper in the wall. This is because the south wall actually faces a few degrees off south.

We owe it to Mrs. J.G. van Cittert-Eymers (Ph.D.)*, president of the University Museum from 1955 to 1968, that we still have this unique pole style dial. In the 1970's, she found this sundial was in a deplorable state.
Realizing that this dial was an exceptional "historic document in the history of time measurement", she had the sundial restored and reinstated. It would otherwise surely have landed on the rubbish heap during the restoration of Jacobi Church at that time.

A revolution in time measurement

During and before the Middle Ages, man lived according to natural time. Day and night each counted twelve hours, so that in summer, day hours were much longer than night hours.
In winter, night hours were longer and people slept longer.
Wherever sundials were used, they were adapted to these unqual hours that slowly varied according to season.

The turn came arond 1350, when equal hours, such as are in use today, came into use. The new system was introduced gradually.
The Frankfurt and Konstanz archives, among others, give times during the transition period in both equal and unequal hours

The revolution was aided by the use of mechanical timepieces: church clocks. They had come into use a little before and indicated time in equal hours.
These clocks had quite irregular movements and continually had to be adjusted using sundials.
But sundials indicating equal hours did not yet exist.
This led to a new invention: the pole style sundial.
This had a style directed towards one of the celestial poles. The shadow behind such a style turns through exactly fifteen degrees per hour.
It was really a simple invention, but it would have been pointless during the earlier period when unequal hours were used.
This type of sundial, which by the way can take on various shapes (as long as it contains a north or south celestial pole pointing style) has since supplanted practically all other types.

How is it that Utrecht posesses such an early example of the pole style sundial?
We have a small clue:
In 1441, Dutchman Johannes de Laet was in Erfurt, where he copied a number of treatises on pole style sundials.
The first treatise was written ten years before in Neurenberg, and more followed quickly. Unfortunately, there is no direct evidence that Johannes de Laet was involved in the 1463 Jacobi Church sundial.

Of course, many more "modern" sundials must have been made during the second half of the fifteenth century, and lost again.
But Utrecht alone posesses the remaining dated pole style sundial from the beginning of the revolution in time measurement.

After restoration

* In 1972, Mrs. Van Cittert wrote "Sundials on and around buildings in The Netherlands".
In collaboration with Mr. M.J. Hagen, a greatly extended publication was completed in 1984: "Sundials in The Netherlands".
It was this Mr. Hagen who, in 1978, initiated the founding of the Dutch Sundial Society.

J.A.F. de Rijk