The Amsterdam Sundial Trail
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Bonus: some more Amsterdam sundials
Sundial by David Coster (ca. 1676-1752)
This is a unique sundial, one of the most distinguished in the country! It has a copper face, size 42 by 42 cm, and a brass gnomon, 13 mm wide.
According to the coat of arms, it has been made for Unico Wilhelm, Count of Wassenaer (1692-1766). The waxing moons allude to his name. The latitude, 52° 15' matches Twickel Castle, in Delden (province Overijssel), where Unico lived. Besides his diplomatic and administrative activities he was a gifted composer of baroque music.
The time scale runs from 3:40 a.m. to 8:20 p.m., from the inside outward increasingly divided, down to 1 minute. The noon gap accommodates the width of the gnomon.
The center part of the dial shows many details:
- a wind rose, divided into 64 points, 16 of which are named;
- along the south side the signature of the engraver: D.Coster Sculpsit;
- around the north side three ribbons, which provide the corresponding times in Batavia, Madrid and Mexico;
- next, the time in Rome, in Italian hours, from 12:30 to 21:30 hr, for the summer half-year only. Date lines per 10 or 15°. The nodi are two short pegs on the sides of gnomon (visible in the first photo above).
The most exceptional feature, however, is the mean time scale in the northern part of the center.There are actually two discrete dials, which each had their own gnomon, a peg placed in the holes in the corners. The left (eastern) dial serves the morning hours, the other the afternoon. The hour lines are figure-8 shaped, or analemmas, so as to account for the equation of time. Thus the label 'EQUATIO TEMPORIS'.
The date lines are not given per zodiacal month, but per quarter-hour of sunrise and sunset, according to the scales 'SON OP' and 'SON ON-DER'. Again, these only cover the summer half-year. Which side of the analemma should be used, is indicated by the extensions of the curves to the nodes marked 'Langende Dagen' (lengthening days, 21 March to 21 June) and 'Kortende Dagen' (shortening days, 21 June to 23 September).
The analemmas and date lines run up the sides of the gnomon, as can be seen for the morning dial here. The date lines are extended into the winter half-year, downto sunrise at 7:15 a.m. and sunset at 4:45 p.m.
Who is the designer of this sundial, and when was it made?
Marinus Hagen made an extensive study of the sundials by David Coster. He suggested that either Willem Jacob 's Gravesande (1688-1742) or Nicolaas Samuel Cruquius (1678-1752) might be the inventor. Both had extensive scientific contacts in London and were members of the Royal Society.
Based on the coat of arms, the sundial should be dated somewhere between 1719 and 1733. The value of the EoT was accurately known in the mid of the 17th century already; the first table was published by Christiaan Huygens in 1665. Its primary use was to regulate clocks according to the sundial, so as to read local apparent time. To my knowledge, this sundial is the first one that enabled direct reading of local mean time.
Garden of Keizersgracht 524
What makes the next sundial special is not the dial itself, a rather simple armillary sphere, but the story behind it. The Rijksmuseum has a painting by Hendrik Keun from 1772, depicting the garden and coach house of the house Keizersgracht 524. The painting is presently in Rijksmuseum Twenthe in Enschede, on loan from the Rijksmuseum during the restoration works.
Dating from 1758, the coach house is among the most beautiful ones in Amsterdam. The façade in Louis XV style has two decorated recesses, in which statues of Ceres (?, with lamb) and Hercules (with lion). In front of the two-story coach house is a one-story garden house, and in front of that a sundial. It resembles the one in the garden of the Rijksmuseum, in that it has one ecliptic ring, lacks tropic and polar rings and the pole-style bears a small sphere. Note also the reflection of the rings in the window of the garden house, which cannot have been there in reality. In 1976 a replica of the sundial was made. Presently it requires some maintenance.
The sunlit scene of the painting is an interesting one for sunwatchers. Can we derive the position of the sun from the shadows we see? And from that determine the date and time at which Hendrik Keun captured the view? This assumes, of course, that the presentation of the scene is true to life. Which I doubt.
Look at the shadows. Some are sharp, as with a clear sky: the shadow of the roof behind us, in the foreground, and of the left hedge on the garden house. Others are vague, indicating a slight overcast (not uncommon in the Netherlands...): at the two men on the right, the two ladies and the flute player in the back and the statues above them. The shadow of the sundial is intermediate. A rough estimate is that it makes a 45° angle with the garden's center line. As the declination of the coach house is about 135° east, the sun thus should be about due east.
And the altitude? Judging from the statues, perhaps some 20°. This azimuth/altitude pair occurs here shortly before 7 a.m. local time in early May or early August. These people were early risers, then! However, the shadow of the left hedge on the garden house suggests a much larger altitude.
Another cue might be obtained from the vegetation. In the arabesque beds hyacinths and daffodils flower, which occurs in April. At the same time we see flowering roses, tied up along stakes. However, this occurs in June at the earliest. Also the trees are fully in leaf; uncommon in April.
In conclusion, the painter apparently took some artistic liberties to make the scene more attractive.
Weesperzijde
Colorful sundial on a house dated 1884 and overlooking the Amstel river. Dial face in mosaic work. Incorrect layout of hour numbers. The hour scale suggests a slightly westerly declination, but the façade declines 70° west.
Valeriusplein
Sandstone sundial on the (right-hand) corner of this Amsterdam School house, located on Valeriusplein. Hour lines from 6 a.m. to 6 p.m. and short half-hour lines. The gnomon and its fixing are shaped like a nose and eyes. On the left part a figure is engraved, maybe an Egyptian god. Distributed around it the motto "Ik tel alleen de zonnige uren" (I only count the sunny hours).
Haddonstone dial in private garden
In a garden near the Rijksmuseum, visible from the sidewalk, is a horizontal brass sundial. This is model X710 of the Haddonstone company, from East Haddon (Northamptonshire, England). Diameter ca. 40 cm. The dial face and gnomon are beautifully engraved. A sun face in the center, four time scales with increasingly fine divisions, down to 5 minutes. Roman hour numbers from 4 a.m. to 8 p.m. Inside the time scales the motto “Make time, save time while time lasts. All time is no time when time is past”. A windrose near the gnomon foot.
What is special of this design is that the pole-style is formed by the lower edges of the gnomon. This is sometimes called 'à la capucine'. In that case, there should be no noon gap, but a noon overlap. Strangely enough, the dial has an 8 mm noon gap, although the gnomon is only 4 mm thick. Apparently the sundial face was designed for an 8 mm wide 'normal' gnomon.
The dial was designed in the 1980's and set to middle England, wherever they are sold in the world. Fortunately, Amsterdam is at about the same latitude.
