Bulletin 03.1 English summary

R. Hooijenga.

Contents of the January 2003 Bulletin, nr. 81

4 Members, meetings, agenda. Secretariat
One new member, bringing the number of paying contributors to 155, not counting honorary memberships. - The Anniversary meeting is on 28 June, the fall meeting is on 29 September. – The Web address of the Society is now http://www.de-zonnewijzerkring.nl

6 WEB site of De Zonnewijzerkring. Secretariat
Until now the Society used the secretary’s homepage, but now we have our very own web space. The site is also a lot bigger. Four main columns are: Sundial of the month, featuring a different dial with description and photo; Article of the month, highlighting an interesting idea in dialling; Work by members, on sundials made by members or in the realisation of which a member played an important part; and Advertisements – not the garden centre variety, but where members can describe what they have to offer and place links to their web sites.
The material in the first three columns is archived and so available in later months or years as well.

7 Bulletins 1-80 on your computer screen. F.J. de Vries
Practice your Dutch and learn to read mediaeval typewriter fonts! The priceless CD contains bitmaps of ALL the pages of ALL the Bulletins 1 – 80, and even better, there is a searchable index. For example, just type “bifil” (to catch all the spellings), and you are instantly referred to everything the Bulletin has ever had to say on bifilar sundials!

8 The editorial office. F.J. de Vries
A concise explanation of everything that has happened before a paper appears in the Bulletin. Most anything is fit to print, but sometimes a bit of editing can make the text more enjoyable.

9 Meeting of 21 September 2002. Secretariat
W. Coenen reported on the anniversary plans. D. Verschuuren is making an inventory of Society property. – A. Verhoeven gave a talk on the Yabashi point. He combined a Yabashi point sundial with a circular scale with a Foster dial that uses the same scale. – A. vd. Beld, using an idea from an 18th century penny, made an “eternal” calendar for 1978-2020. Everyone present received a copy. – H. Hollander showed his drinking-glass sundials for morning- or afternoon hours. In pairs, these cup dials work all day. – F. de Vries talked about the 1564 sundial recently excavated in Friesland. – D. Verschuuren is sculpting a conical sundial and relates of the problems met with in carving a cone out of stone. He finds a skaphe easier to make.
– A. Schoorel is building an analemmatic sundial in Vlissingen. The dial will see limited sunshine, and it was suggested to lay out only the usable hour lines. This idea is rejected because of the educational value of the full set. – J. de Rijk shows pictures of children in Tehran making a butterfly sundial. Professor Bagheri “translated” De Rijk’s dial into an Iranian version.
Fabio Savian developed a new version of the bifilar sundial. F. de Vries explains how the shadows of not only the two crossing wires, but of the hour lines as well, are read together on a surface.

11 Three kits to build at home. J.G.T.M. Taudin Chabot
“Ipacity” sell paper kits. Not just paper, and not just kits – you are building actual working gear that will last longer than you may think possible. The author describes three that he has built.
The “Digital Sundial” is readable to within five minutes. This is possible because it projects the shadows of the numbers and dividers on a figure-of-eight curve. The description, in German with a Dutch translation, is good but you have to stay alert. The bottom turned out a bit convex, and the author solved this with a thick piece of cardboard glued under the sundial. Results are good.
The Jacob’s staff measures horizontal or vertical angles. All parts are cut out from two sheets of paper, somewhat thinner than the cardboard used for the other two kits. This kit is cheaper, too. The useful range is 1 to 40 degrees. This large range is possible because you can slide the runner on the staff in two different ways, and because of the two different sights. The subranges are 1º – 1º55’, 6º15’ – 13º, 1º55’ – 7º30’ and 12º15’– 40º.
The Universal Ring Dial is classic, and this kit is beautifully done. The guide is excellent, but it is still advisable to read ahead one or a few points to see what lies ahead, and to test moving parts before applying glue.
The ring dial has a declination scale as well as a date scale. It is truly universal, in that it works in both northern and southern latitudes – something not often seen in sundials.
For more information, find Ipacity on www.ipacity.nl

14 The Met Office’s sundial. M. Hugenholtz The Royal Dutch Meteorological Office publish suntrack graphs for 51, 52 and 53 degrees latitude. The author describes a sundial construction that uses the numbers from these graphs. Referring to Fig. 1, â is the latitude. Let OPP' be a style triangle rotated about OP into the horizontal plane left of the N-S line, and UPP" the edges of a vertical surface A, also rotated into the horizontal plane. The azimuth AZ, from the graph determines line S. P'P" = PP'. Line H is determined by the altitude h, also from the graph. The intersection of H and S, U, is a point of the hour line OU for that time.
An advantage is that date or declination lines are easily found as well as the hour lines: connecting all the U's gives the declination line for the declination chosen for the construction. – Fig. 2 shows the construction for a declining vertical dial.

17 Locating the sun in the sky. H.W. van der Wyck
The author establishes a reference system and then introduces the various variables dealt with. Next, using spherical trigonometry, he derives equations to calculate local co-ordinates for the sun from latitude, longitude, date and time.

18 Sundial Park Genk #5: The Euro-meridian. F.W. Maes

22 Introduction to Gnomonics, part 2. F.J. de Vries
Co-ordinate systems, terrestrial navigation and celestial navigation are in this part. Some stress is placed on the need for rigorous conventions as regards signs, reference points and so on. From the local horizon system, we progress through declination and hour

27 1564 polyhedron - continued. F.J. de Vries

28 Zaltbommel book dial. F.W. Maes
When in Zaltbommel, the author went to see the book dial. This is in the collection of the museum in the beautiful house built in 1535 for Maarten of Rossum, field marshal for Charles duke of Gelre.
Unfortunately, the dial was in storage, but manager Bulthuis was very kind and fetched it.
Mr. Maes had ample opportunity to measure and draw the book dial, and a description follows, together with his thoughts about classifications of sundials, and a mention of the modern catalogue database used by five museums in Gelderland (the then Gelre).

32 Shifted Italian hours. F.J. de Vries
A noon line in San Giuseppe Cathedral in Brescia, Italy, gives the time for the summer solstice transit as XV⁴⁵ for Hora Meridiei. Remember, these are Italian hours, which start at sunset. However, there was a system of “shifted” Italian hours, for civil use, which started at 30 minutes past sunset.
Testing the Brescia solstitial Hora Meridiei using “ordinary” Italian hours, we would have to conclude from the formula cos T = -tan ö tan ä and T = XXIV - XV⁴⁵ = 8h15m (123.75°), that ö for Brescia is 52°. Of course it is not; actually it is 45.5°.
Working the other way around, we find that T = 116.18° or 7h45m, which is 30 minutes different from what we found earlier. We may therefore conclude that the Hora Meridiei was XV⁴⁵ in shifted hours.

33 "De Zonnewijzerkring", text and music by: H.W. van der Wyck
A two verse ditty extolling the virtues of the Society and the objects of its affection. Tempo di marcia.

34 Index of names of Dutchmen related to sundials. H.W. van der Wyck
Two-page list of names and sources where mentioned. Of considerable value for historical research.

36 De Zonnewijzerkring: fifth Lustrum. F.J. de Vries
Marinus Hagen founded the Sundial Society in 1978. This year we celebrate our 25th anniversary, a lustrum of lustra. Fer recalls the lustra we had. – 1983: three exhibitions in Utrecht, and the presentation of “The Sun as Clock”, written by Hans de Rijk. The newspaper Zwolsche Algemeene paid for the restoration of the sundial on St.Nicholas. Moreover, the Society presented the City of Utrecht with a plan for an analemmatic sundial on St.Johns Cemetery Square. It was built shortly after. – 1988: an exhibition in the Maritime Museum in Amsterdam. “25 Centuries of Timekeeping” (by Hans de Rijk). Chriet Titulaer delivered the lustrum speech and dedicated the Hans’ book to Marinus Hagen. – 1993: Also the year of the fiftieth Bulletin. This medium binds us all together, and meanwhile we see its concept copied by societies worldwide. And to think we started it! Govert Schilling held a talk on Stonehenge. All members received an “under water” (actually Perspex) sundial. The refractive index of the Perspex distorts the hour lines into a pleasing pattern. – 1998: An entirely different setting: a photo contest. The photos were displayed in Den Dolder, where Prof. Baudet speeched. The widow Hagen received the book “Sun and Time”, a compilation of the most important of her late husband’s papers. De Rijk, Taudin Chabot and De Vries edited this book. Again, all members received a small sundial based on a penny. Member Fer Wilbrink made these dials completely gratis. – 2003, the fifth lustrum: the celebration is on 28 June 2003.

38 Solution to the Bulletin 02.2 puzzle (continued). F.J. de Vries

42 The Yabashi point and its applications in sundials. A. van der Hoeven
A Yabashi-circle is a circle drawn in such a way that its perimeter is cut in equal parts by the hour lines of a horizontal or vertical sundial. This is not possible exactly, but a distance e and “starting angle” a₀ for the 12 o’clock line exist for which the errors are minimal. The author finds an error of around four minutes. He uses two gnomons, each for half the solar day. – One of the advantages of equiangularly spaced hour points is the ease with which longitude and eot corrections are performed.
A special interest of the author is the auto-aligning sundial, for which the direction of the local meridian does not need to be known. He combines the Yabashi dial with a Foster-Lambert dial, which is a derivative of the analemmatic. An F-L dial has a circular equiangular scale, and therefore it was possible for the Yabashi and the F-L dial to share the same scale.
However, in the Yabashi dial, the noon line is not a diameter of the circle, and so Foster-Lambert dial had to be set forward by a certain constant amount of time. The author has solved this with a cylindrical gnomon, reading the edge of the shadow. The two Yabashi gnomons flank the cylinder. In the afternoon, the other Yabashi gnomon and the other side of the cylinder are used.
When does one of the dials eclipse the other? A moment’s reasoning showed this to be at sunset and sunrise, and hence not much of a problem.
To eliminate the need for the moving F-L gnomon, one might use a set of scales on a cylinder, slanted by j and with a circular intersection with the horizontal.

46 “Bornfelt” sundials. H.W. van der Wyck
Pewter sundials cast from a slate mould signed Bornfelt are for sale in the Dutch Timepiece Museum for € 40,- (with certificate). – The catalogue to the large TIME exhibition of 1990 lists two Bornfelt dials, but erroneously reports them as signed “Born fecit”. In fact, it says Bornfelt here as well.

47 Literature 1446 - 1458. D.L.J.M. Verschuuren