Italian “Machina Mercurialis exhibens motum Mercurii in Ellipsi circa Solem inequabiliter progredientis” – Mercury Machine showing the irregular elliptical motion of Mercury around the Sun. The other instrument is an Italian quadrant. The unique 18th century Italian Machina Mercurialis shows the peculiar eccentricity of Mercury’s orbit around the Sun. This explains why the planet, seen from Earth, speeds up and slows down. In its perihelium the distance of the planet to the Sun is only 46 million kilometers, in the aphelium de distance is 70 million kilometers. The perihelium of the orbit moves very slowly around the Sun. This is called the precession. In the 19th century astronomers observed Mercury very carefully but couldn’t explain the irregularities of its orbit simply using Newton’s laws. This led to the supposed existence of another planet between Mercury and the Sun, called Vulcany and influencing Mercury. Only Einstein’s General Theory of Relativity gave the real answer to the question of Mercury’s erratic behaviour.