Bulletin 99.3 English summary

R. Hooijenga.

Contents of the July 1999 Bulletin, nr. 70

Recently two special papers, by members Jan Kragten and Wiel Coenen, appeared. These papers, containing invaluable data, warrant publication of an extra Bulletin.

Jan Kragten has studied data on Roman and Greek antique conical sundials for several years. He is especially interested in the accuracy of these dials. He based most of his study on the book "Greek and Roman Sundials" by Mrs. Sharon L. Gibbs (Yale University Press, New Haven and London, 1976). This book contains data on many specimina, scattered over several museums all over the world.

From the given measurements, Jan has in each case tried, by calculation, to establish if the sundial should be classified as good or poor.

It appeared that one single method of analysis was not sufficient. Of a certain dial not all measurements were always available, and some data were in error, either due to erroneous measurements, or to printer's errors.

For this reason Jan has developed five methods for determining a dial's quality.

The results of his study are presented in this Bulletin. Only conical dials are treated; a treatise on the quality of hollow spherical sundials (Skaphes) currently has his attention.

Jan discusses 40 samples from the Gibbs book, judging the quality of each.

Marinus Hagen published supplements to the book "Zonnewijzers in Nederland" (Sundials in The Netherlands) (Walburg Pers, Zutphen 1984) in May 1989 and in January 1992. Later the column by the same name, in the Bulletin, served that purpose. As time went by, the need for a completely new work made itself felt.

The author has set out to satisfy this need. Using the same format Hagen did, he lists all the dials that have appeared in the Sundials in The Netherlands columns along with Bulletin number and page of publication. This means some dials are listed that are no longer in existence. The new list is cumulative, including the 1989 and 1992 data which have been revised where necessary. The old supplements can be discarded.

An annex lists Bulletin articles on certain dials. The sundial list refers to them by numbers.

A second annex contains sundial mottoes. This is not a comprehensive list.

With the appearance of this new Supplement all known data about Dutch sundials is once again readily available. But 15 years after "Zonnewijzers in Nederland" (the book) appeared, one ponders the possibility of a new, completely revised, book; either along the lines of the 1984 one or a new concept with a different title. Both options bring with them many consequences, and it remains to be seen if anything comes of it.

For the time being, we should be content with what we have. At least an important step is made.

The actual text is highly mathematical in nature. This work will be translated in English later. Please check with the author for availability by that time.

The methods seek to reproduce the working of the sundial from the measurements given in the available data. Some methods are very sensitive to small errors in measured data. Others are less so, but in some cases the needed angle or length was measured quite inaccurately.

In many cases the author was able to establish that the sundial under scrutiny was actually quite good.

A figure showing the dial plate of a moon dial. One has to take the age of the moon into account and read the dial accordingly (of course, the moon's position on the celestial sphere changes so quickly that one rarely knows the age sufficiently accurately for a result anywhere near decent).

It will be clear that this text does not lend itself well for summarising. Anyone actually using it in earnest should have to be at least a little conversant with the language anyway.