Zoellner's belief in the genuineness of Slade's mediumistic marvels led him to write a curious work, entitled, "Transcendental Physics," being an inquiry into the "fourth dimension of space." Poor old Zoellner, he was half insane when these séances were held! We have the undisputed authority of the Seybert Commission for the correctness of this statement. In Hamburg, Dr. Borchert wrote to Slade offering him one thousand marks if he would produce writing between locked slates, similar to the writing alleged to have been executed at the Zoellner séances, but the medium took no notice of the professor's letter. The conjurer, Carl Wilmann, with two friends, had a sitting with Slade, but without satisfactory results for the medium. "Slade," says Wilmann, "was unable to distract my attention from the crucial point of the trick, and threw down the slates on the table in disgust, remarking: 'I can not obtain any results to-day, the power that controls me is exhausted. Come tomorrow!'" That tomorrow never arrived for Wilmann and his friends; Slade did not keep his appointment, nor could Wilmann succeed in obtaining another sitting with him. The medium had been warned by friends that Wilmann was an expert professor of legerdemain. It was in 1886 that Slade created such a furore in Hamburg in Spiritualistic circles. A talented conjurer of that city, named Schradieck, after a few weeks' practice succeeded in eclipsing Slade. He learned to write in reverse on slates, and produced writing in various colored chalks. Another one of his experiments was making the slate disappear from one side of the table where it was held _a la_ Slade and appear at the opposite end of the table suddenly, as if held up to view by a spirit hand. Wilmann describes the effect as startling in the extreme and says Schradieck produced it by means of his left foot. After Slade's departure from Hamburg, spirit mediums sprang up like toadstools in a single night. Wilmann in his crusade against these worthies had many interesting experiences. He gives in his work "Moderne Wunder" several exposes of mediumistic tricks, two of which, in the sealed slate line, are very ingenious. The medium takes a slate (one furnished by the sitter if preferred), wipes it on both sides with a wet sponge, and then wraps it up carefully in a piece of ordinary white wrapping paper, allowing the package to be sealed and corded _ad libitum_. Notwithstanding all the precautions used, a message appears on the slate. It is accomplished in this way. A message in reverse is written on the wrapping paper with a camel's hair brush or pointed stick, dipped in some sticky substance, and finely powdered slate pencil dust is scattered over the writing. At a little distance, especially in a dim light, it is impossible to discover the writing as it blends very well with the white paper. In wrapping up the slate the medium presses the writing on the paper against the surface