Practical Psychomancy & Crystal Gazing by New Thought pioneer William Walker Atkinson deals technically with a clairvoyance technique using the crystal ball, once a popular instrument of Gypsy fortune tellers. Atkinson explains the technique within the framework of psychomancy, in which the crystal ball (just like the black mirror) functions as the “TV screen” of an astral tube. An astral tube is in essence a thought form or servitor that serves as an intermediary between the earthly and the astral world.