Fig. 8
From: Spectacular rediscovery of the original prints of radiographs Roentgen sent to Lorentz in 1896
a, b Two radiographic images of a leaden cage that surrounds the gas discharge tube. The difference between them is that the second image was taken while the cathode rays were deflected using a magnet while in the first image the magnet was absent. Between the two radiographs, the shadow of the leaden cage moved. Roentgen concluded from this that the X-rays had to emanate from the point on the glass wall of the discharge tube where the cathode rays impinged and this point had moved as a result of the deflection of these cathode rays. It can be noticed that the magnet pulls the focal spot downward, resulting in the central ray to hit the center of the cage (shadow of the ribs at the top of the cage bend upward and the brightest part of the background moves downward) while, at the same time, the focal spot becomes smaller (image becomes sharper). Respective manually written legends: ‘Entladungsapparat mit Bleikäfig (Kathodenstrahlen nicht abgelenkt)’(Gas discharge tube with leaden cage (cathode rays not deflected)) and ‘Entladungsapparat mit Bleikäfig (Kathodenstrahlen d[urch] (The word ‘durch’ was completed by the author) Magnet abgelenkt)’ (Gas discharge tube with leaden cage (cathode rays deflected by a magnet)). Paragraph referral: § 12 (in both radiographs)