“Notwithstanding his unfairness in the Algerian affair, Robert Houdin, an authority on the art of prestidigitation, and Moreau-Cinti, another, gave honest testimony in behalf of the French mediums. They both testified, when cross-examined by the Academicians, that none but the “mediums” could possibly produce the phenomena of table-rapping and levitation without a suitable preparation and furniture adapted for the purpose.
They also showed that the so-called “levitations without contact” were feats utterly beyond the power of the professional juggler; that for them, such levitations, unless produced in a room supplied with secret machinery and concave mirrors, was impossible.
They added moreover, that the simple apparition of a diaphanous hand, in place in which confederacy would be rendered impossible, the medium having been previously searched, would be a demonstration that it was the work of no human agency, whatever else that agency might be.
The Siecle, and other Parisian newspapers immediately published their suspicions that these two professionals and very clever gentlemen had become the confederates of the spiritists!”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 