Arthur Conan Doyle 
The Edge of the Unknown [EPUB ebook] 

Who was the greatest medium-baiter of modern times? Undoubtedly Houdini. Who was the greatest physical medium of modern times? There are some who would be inclined to give the same answer. I do not see how it can ever now be finally and definitely proved, but circumstantial evidence may be very strong, as Thoreau said when he found a trout in the milk jug. I foresee that the subject will be debated for many years to come, so perhaps my opinion, since I knew him well, and always entertained this possibility in my mind, may be of interest. If others add their experience in order to support or disprove my own surmises, then some result may eventually be obtained.