Figure 1
South front of the city palace in Berlin around 1900. The chamber of stars was located on the first floor above gateway number 1 (red dot).
Figure 2
(above) Paul Spies (1862–1925). In 1896, he was a physicist at the Urania, Berlin. (below) Urania institution, Invalidenstrasse 58, Berlin in 1900 [33].
Figure 3
Reinhold Burger (1866–1954). In early 1896, he was a pioneer in manufacturing X-ray tubes in Berlin [47].
Figure 4
Drawing illustrating the lecture given by Paul Spies at the Reichstag on 13 February 1896 [49].
Figure 5
(left) Drawing by Paul Spies of the X-ray tube with a circular anode designed by Reinhold Burger [48]. (middle) Magnified view of the circular anode of the X-ray tube shown in Figure 4 [49]. (right) Rebuilt original X-ray tube of Reinhold Burger, in regular use by Paul Spies [47].
Figure 6
Karl Heinrich von Bötticher (1833–1907). Photograph between 1880 and 1900. https://www.bild.bundesarchiv.de/dba/de/ Bild 146-2008-0022.