Imaginary Experiment with "Lumen."--Impossibilities.--A Destroyed Illusion.--Is the World Infinite?--Surface Creatures and Shadow Rambles.--What is the Beyond?--Action at a Distance.--Ideas of Multi-dimensional Regions.--Hypnotism.--Recollections of Zöllner.--Science and Dogma.--The Trial of Galilei. CONVERSATION held during April 1920 destroyed an illusion which had become dear to me. It concerned the fantastic figure, "Lumen," conceived as an actual human being, imagined as endowed with an extraordinary power of motion and keenness of sight. Mr. Lumen is supposed to be the invention of the astronomer Flammarion, who produced him in the retort of fancy, as Faust produced Homunculus, to use him to prove the possibility of very remarkable happenings, in particular, the reversal of Time. Einstein declared outright: "Firstly, Lumen is not due to Flammarion, who has derived him from other sources; and secondly. Lumen can in no way be used as a means of proving things." MOSZKOWSKI: "It is at least very interesting to operate with him. Lumen is supposed to have a velocity greater than that of light. Let us assume this as given, then the rest follows quite logically. If, for example, he leaves the earth on the day of a great event, such as the battle of Waterloo, and---- May I trace out this example, at the risk of tiring you?" EINSTEIN: Do repeat it, and act as if you were telling something entirely new. It is clear that the Lumen-story gives you great amusement, so please talk quite freely. But I cannot forgo the privilege of showing later how the whole adventure and its consequences must be demolished.