Bulletin 05.1 English summary

R. Hooijenga.

Contents of the January 2005 Bulletin, nr. 87

Members, dates, miscellaneous. Secretariat. 3
One new member, four resigned or passed away. – Fer saw a shadow plane dial in Tiel (photo). Thirteen stone slabs, marked 9..21, plus one horizontal noon slab, fixed in a concrete subsurface frame. – A correction to An introduction to Gnomonics (equations).

Nijmegen to have 'Column of the gods'. City of Nijmegen. 5
The discovery, in 1980, of remnants of a Roman 'Column of the gods' from the year 17 AD meant a definitive recognition of Nijmegen as the oldest Dutch city. The city's 2005 anniversary will see the raising of a new granite column, with a bronze base made with replicas of the found fragments. The Zonnewijzerkring was approached because of the sundial aspects of the column's shadow on the square.

Account of the meeting of 25 September. Secretariat. 6
Twenty people attended, among them one from Spain and one new member – Introduction of the new chairman Mr. Dik de Groot – A "floating" sundial by Holman (photo) – Cylinder sundial by Hollander (photo) – Spruijt shows a circular, horizontal sundial by Fraser of Bond St, London, sometime after 1751 – CD-dials by De Rijk and Sasbrink and a spar dial made of two chopsticks and a skewer by De Rijk – 'Van Bierum' block illustrating the evolution from equatorial to horizontal sundial by Roebroeck.

Eble's Horoscope: supplement. A.J.M. vd. Beld. 10
Another proof (different from the one in Bulletin 03.2, pp 28-31) that the Horoscope satisfies the equation for sin(h) and is therefore a correct altitude dial. The article uses the original drawing with points u, v, w added. Follows the proof (error: the first semicolon should be omitted). The author also derives the shape of the hour lines: the noon line is a circle of radius ms = 1 centred on m. The other hour lines are scaled with respect to the noon line with a factor cos(t) in the direction of pr, that is, they are ellipses having a semimajor axis of length ms = 1 along mp, and a semiminor axis of abs(cos(t)). For 6 and 18 hours, this degenerates into a straight line.

Sundials in The Netherlands. A.G.M. Bron. 11
Gelderland: Heukelum 01, Heukelum Castle. This sundial features in the Zonnewijzerkring's Bulletin device. Made in Harlingen in 1914, its marble began to crystallise in 1995 and the dial was replaced by a copy. The original broke in two on removal. Noord-Brabant: Gemert 01b, Gemert Castle. In room 63, now hidden under the wall-to-wall carpet, there is an equation-of-time loop made with some 8000 tacks in the wooden floor. The photo of the north side is a first: a heavy cupboard covered it for years. It is believed that the loop is from around 1900; its purpose remains unknown.

The sundial of Emperor Augustus. F. W. Maes. 14
Everyone, who does anything at all concerning sundials, is likely to have seen Buchner's reconstruction drawing of Augustus' Sundial on the Campo Marzio. To be sure, there is more to be said about this alleged sundial. Maes' authoritative eleven-page article delves into the subject in some detail, and deserves greater circulation, perhaps in a later professionally done translation. For the moment, I will have to limit this summary to his conclusions as summed up at the end of the paper:
1. There is no plausible argument for Buchners' hypothesis that the obelisk of Augustus should have served a sundial. 2. On the Campo Marzio was the meridian of Augustus (see Pliny), that could be used for calendrical, astronomical and astrological observations. 3. Buchner excavated a meridian from the first century AD – a singular find, deserving more attention from archaeologists. 4. Topographical relations between Augustus' edifices were quite loose - certainly not to centimetre accuracy.

Co-ordinate transformer on the web. J.G.T.M. Taudin-Chabot. 25
Of Dutch national interest mainly, this web application calculates geographical co-ordinates to and from important reference frames.

A single-day sundial. Willy Ory. 26
Jos Geusens designed this sundial for Open Monument day. He and Willy Ory built it on the grounds of Castle Nieuwenhoven near St. Truiden.
On the day for which the dial was designed, 11 September 2004, the shadows of the tops of the "matchsticks" passed through their respective hour points on the noon strip at the appropriate times. The design would also work on 2 April, but the dial did not live that long.

Time is out. Jan Degraeve. 28 Seth Atwood has sold the remainder of his remarkable Time Inn collection at Sotheby's on 13 and 14 October 2004. His collection contained those pieces that represent important changes, improvements, evolution; many were unique or rare. Eventually, with his relatives showing little interest, Atwood entrusted an important part of the collection to the Adler Planetarium and made the remainder available to hundreds or thousands of collectors.

Photos of the Eenrum-Groningen Twin Dial. E.L.H. Roebroeck. 30
A well-proportioned, almost ideal, tower. Roebroeck chose to make a modest sundial to the Southwest, the only direction enabling a view on the sundial from farther away. Photos show: the tower, the Mayor, model (paper, cardboard, wood), sundial, 1:10 model of Eenrum tower, mini-dial for this model, design sketch, inclination and easting of the tower, drawing of easting, alignment of south dial, tower (top is vertical, base is inclining), how to find Polaris (three photos). From the list of remarks: "the top style support of the West dial is designed so that no bicycle tyre – however well thrown – will hang off it."

No-math, arbitrary plane, pole style dial. H.W. van der Wyck. 34
How to construct a pole style sundial on an arbitrarily oriented plane, without formulas, using plane geometry only plus some tools: a plumb line, square, a custom right-angled triangle one of the corners of which equals local latitude, and a rod for the pole style ("gnomon"). The construction: 1. Draw meridian M on the plane (see the figure). 2. Raise the pole style, vertically over the meridian and under the correct angle with the horizon, using triangle and square. 3. Project an arbitrarily chosen point of the pole style onto the plane, using the square. 4. Draw substyle OS from the projection to the gnomon foot. 5. Draw equator Eq square to the substyle. 6. Mark the distance a, between the intersection of equator and substyle and the style (square to the style), on the substyle, from the intersection. 7. Draw a line from the point on the substyle found in 6 to the intersection of equator and meridian. 8. Draw angles every fifteen degrees, either side of the line found in 7, through the point from 6, using compass or protractor. 9. Lines from the pole style foot to the intersections of the lines from 8 with the equator are the desired hour lines!
The author further describes a construction to find the declination.

Oldie: Noon mark in Haren-Groningen. E.L.H. Roebroeck. 36
If we can agree that "time" equals "place of the sun", then a noon mark is a device for determining mid-day in the most literal sense of the word. Along with a discussion of the difference between legal and apparent time, the noon mark is described. Its length is so chosen that the shadow of the gnomon just touches the top or bottom at noon at the solstices, or beginning of winter or summer. Near the soldier course in the wall, a small horizontal indicator marks the equinoxes, when spring or autumn starts.

Did you know? Can you prove it? - part 4. F.J. de Vries. 38
Fer found a more general theorem by Emerson, which states: "choose an hour line; intersect it with a line, parallel to the hour line for an hour angle 90 degrees different; the other hour lines divide the new line in symmetrically equal lengths". In particular, diagonal AC in Hans' drawing is parallel to the 9-hour-line, and so its divisions are symmetric around its intersection of the 3-hour line. – The article then proves the 1770 Emerson theorem, and concludes with the original English text of the proposition.

Dialing scales generalisation. F.J. de Vries. 41
The Emerson proposition also leads to a more general way to look at dialing scales. Instead of having symmetry around 45 degrees, other choices become possible. The article shows scales for s = 30 and s = 60. For a narrow range of latitudes, an optimum s exists for which the latitude scale spread is best. For phi = 45 we get optimum s = 45 – the traditional value.

A horizontal sundial on the South Pole. H.W. van der Wyck. 46
A description, taken from Southafrican newspaper clippings, of the "Proudly Southafrican" sundial on the SANAE base on Dronning Maud Land. A usual horizontal dial in design, the materials used are special, being specifically selected for the arctic climate.

Literature 1512 ... 1520. D.L.J.M. Verschuuren. 47