Written by Houdini & Dunninger as a rebuttal to late Victorian/Early 20th Century Spiritualism & Seances, it outlines the tricks used by Mediums & Spiritualists and explains (for the most part) how their "communications" were effected.
Houdini, of course, the world famous magician and escape artist, and Dunninger - at the time as well a famous stage magician.
Now, describing all the various effects they accomplished - glowing instruments hanging in the air and being played by invisible spirits, the casts of limbs in paraffin, the writing on slates, levitating tables, glowing ectoplasm & cheesecloths coughed up by mediums, spirit photographs, the bar back in the day was a heck of a lot higher. I say this because once I was invited to a "similar" event hosted by a popular radio psychic in Airdrie, and not a single one of these tricks were employed, nothing, in fact, that would convince the even the most gullible of idiots there was "another side" that was being drawn upon. But, oddly enough, she was pretty popular in Alberta. Look at the politics and go figure.
Now, in the explanations (and the descriptions of the seances, which Houdini and Dunninger frequently attended with no other intent than to debunk) they frequently call upon a confederate (or 2, or 3), as well as the occasional dwarf (to fit inside hidden compartments in the Spirit Cabinet, or under the floorboards or wherever they might be needed. Discount dwarves are no longer a dime a dozen, which might somewhat explain how the standards have slipped...
Humorous, albeit not terribly enlightening, although it amused me to think of how they spent their spare time, tracking down and enjoying other "Magicians" who frequently were making even greater sums than they were for performing (poorly) but a small repertoire of tricks. Their exposing of them fits in with a long line of Magicians exposing frauds, including Johnny Carson (vs Uri Geller), The Amazing Randi and Derren Brown. Yet for all the exposes and abundance of evidence to counter these miracles people still choose to believe...
I'm in the wrong business...