Hypnoscope

Hypnoscope is an instrument intended to determine a person's susceptibility to hypnotic influences.

[1] Plenty of hypnotists, like Mesmer and others, proclaimed that the human body was susceptible to magnetic fields.

Patient had to put the finger inside the magnetic field, and if he had felt any influence he was considered a hypnable person.

[2] Some psychologists, like Julian Ochorowicz[3][4] or Gessman,[5][6] created their original hypnoscopes for testing hypnability of their patients.

The instrument and the method met some serious criticism from Frank Podmore[7] and, eventually, psychologists lost their interest.