This universal sun ring comes from the former collection of Rudolf Wolf (1816-1893). Wolf’s inventory dating from 1873 does not state clearly whether the universal sun ring was incorporated into the Wolf collection as a purchase or a donation.
An improvement of the hanging sundial
Like this theodolite, the universal sun ring was also made by Georg Friedrich Brander. Find out more about the manufacturer in the article on the theodolite. He developed the universal sun ring around 1760 as an improvement to hanging sundials such as this one: Hanging sundials were considered rather inaccurate.1 Writing about his universal sun ring, Brander remarked that it could show the “true time of all places” in hours and minutes.2
The sun ring rests on the toothed disc, which is moved by a hand drive and set to the longitude of the location. The inner movable ring is used to set the latitude. The equatorial ring indicates the hours and is set perpendicular to the earth’s axis. The month is set via the slider on the openwork disc. The disc is then turned until the sun’s rays fall through the holes. The small hand on the outer edge shows the time.3
In simplified terms, the universal sundial can be described as a precise sundial. Brander’s sundials, and those of his successors in the Höschel & Brander workshop, were considered the most accurate sundials: They were accurate to within four seconds. Such precision could only be achieved with maximum accuracy in the setting of all important parameters such as season or even location.4
Several universal sun rings by Brander have survived and they are identical, which leads researchers to assume that these instruments were produced in series.5
Sundials were a main focal point of Rudolf Wolf’s collection. The objects of Rudolf Wolf’s former collection are certainly among the most important in the collection of scientific instruments and teaching aids. Therefore, this 3D digitisation project saw several objects from this collection being digitised, including a representative selection of historical sundials from the 16th, 17th and 18th centuries. These are all rare objects, of which only a few still exist. Thus, not only does 3D digitisation enable accessibility regardless of location, it also serves the purpose of (digital) preservation.
Photogrammetry and modelling
The universal sun ring had to be digitised in various states – unfolded, closed, rotated – so that the scales would be fully visible on the 3D model.