Johann Karl Friedrich Zöllner

Johann Karl Friedrich Zöllner (8 November 1834, Berlin – 25 April 1882, Leipzig) was a German astrophysicist who studied optical illusions.

He also successfully proved Christian Doppler's theory on the effect of motion of the color of stars, and the resulting shift of absorption lines, via the invention of a very sensitive spectroscope which he named "Reversionspectroscope".

This measure is very difficult, since the flux difference between the Sun and Capella (one of the bright stars he used) is roughly 50 billion times.

Zöllner attempted to demonstrate that spirits are four-dimensional and set up his own séance experiments with the medium Henry Slade which involved slate-writing, tying knots on string, recovering coins from sealed boxes and the interlinking of two wooden rings.

[9][13] In 1879, Hermann Ulrici brought Zollner's experiments to the attention of scientists in Germany by describing them in an academic journal.

[14] George Stuart Fullerton, the secretary of the Seybert Commission, claimed that Zöllner had an "unsound mind" at the time of the experiments.

[17] Psychical researcher Hereward Carrington in his book The Physical Phenomena of Spiritualism (1907) revealed fraudulent methods (with diagrams of the rope tricks) that Slade may have utilized in the experiments.

[18][19] Psychologist Ray Hyman has noted: Science writer Martin Gardner also exposed the tricks of Slade with diagrams and commented that "Zöllner did some good work in spectrum analysis, but he was supremely ignorant of conjuring methods.