This ring sundial comes from the former collection of Rudolf Wolf (1816-1893). The ring sundial is listed but not dated in Rudolf Wolf’s 1873 inventory, and no mention is made of the manufacturers Christian Jenderich and J. Linzner.1
Portable ring sundials can be traced back to the 16th century. Simple ring sundials consist of a simple metal strip with a hole. Double ring sundials, such as the one shown here, represent a further development of simple ring sundials, but also a simplification of complicated universal sundials.2
Ring sundials were mainly used for travel. The double sun ring is used as follows: The suspension eye is moved until the mark is positioned on the latitude of the location. The two rings are then placed perpendicular to each other. Next, the eye has to be adjusted to the day of observation. After all, the position of the sun depends on whether the day falls in the spring, autumn or summer. Once all of these adjustments have been made, the object can be held in the sun and kept in place by the suspension eye. The meridian ring (the outer ring) is then adjusted to the local meridian. The bar – also called the pinhole – must then be turned until the sunlight falls on the inner edge of the inner ring. The hour can now be read. 3
This is only one of a total of four ring sundials in our collection. Two of them are on display in permanent exhibition “Exploring the Sky – A Look at the Rudolf Wolf Collection” in Semper Observatory. This model can therefore also be used for teaching purposes in connection with this exhibition, as the 3D model clearly illustrates its mode of functioning.
Photogrammetry und modelling
The object was digitalised while hanging. A small holder (shown on the left) had to be built for this purpose. To ensure that the rings would stay in place, we secured them using some museum wax. The animated structures were created manually.