William Walker Atkinson 
Genuine Mediumship or the Invisible Powers [EPUB ebook] 

With the popularity of mediumship increasing, so is the necessity of great training in the mediumship art, and because there is a belief that true mediums are only born, William Walker Atkinson demonstrates that mediumship can be developed. Under the name Swami Bhakta Vishita, William Walker Atkinson wrote this classic treatise on mediumship in 1919.