One of the points Arthur Findlay makes in his book On the Edge of the Etheric is that, in John Sloan's séances, the "trumpet" (a conical device used as a megaphone) would tap sitters on command, responding precisely to their instructions, even though the room was pitch dark. In other words, if a sitter asked to be tapped on the left knee, the tap would promptly follow. According to Findlay there was never any fumbling and there were never any mistakes.
Jan Vandersande, in his book Life After Death: Some of the Best Evidence, reported similar phenomena in séances he personally attended.
Reading these accounts, I wasn't particularly impressed, because I vaguely remembered reading descriptions in M. Lamar Keene's book The Psychic Mafia of how trumpet movements could be faked. But something Findlay said intrigued me. He reported that he had tried to duplicate the trumpet taps in the dark, and was consistently unable to do so. It was just too hard to know precisely where to tap the trumpet in an absolutely dark environment.
This seemed like an easy enough claim to test, so I tried my own experiment. Not owning a trumpet, either of the musical or megaphone variety, I used a cardboard tube that had once held a roll of paper towels. With the lights off, I tried tapping various targets in my living room. I found that Findlay was right. It is difficult, and often impossible, to tap a target in the dark. For instance, if I was aiming for the arm of an armchair, I might get the table next to it or the ottoman in front of the chair. Sometimes I would get the arm itself, but not consistently. Quite often I would tap nothing at all; my "trumpet" would pass through empty space.
After a while, my eyes adjusted somewhat to the dark – the room was not pitch black – and then my accuracy increased. But of course, had any sitters been present, their eyesight would have improved along with mine. If I could see them, they could see me. If the room was just bright enough to allow me to see my targets, anyone with me could have seen me holding the makeshift trumpet.
Then I went back and reread the relevant part of The Psychic Mafia. It turns out that Keene does not discuss trumpet taps at all. He does talk about creating the illusion of a levitating trumpet and making the trumpet whiz about in the air; the first is accomplished simply by lifting the trumpet in the dark, and the second is done by extending a collapsible trumpet to its full length and then waving it about, or by using a rod to extend the trumpet toward the ceiling. But there is no mention of tapping the sitters on command.
I also looked at a similar tell-all book, Revelations of a Spirit Medium. My search for the word trumpet in the online text brought up several references, but nothing relevant to the tapping effect.
Of course, one might argue that the medium is using night vision gear to see what the sitters cannot. This explanation could conceivably pertain to present-day séances, though there would be the problem of smuggling the night vision equipment into the séance room or concealing it beforehand. At any rate, it could hardly apply to Sloan's séances, which were conducted in the 1920s or even earlier.
It might also be argued that some mediums just happen to have unusually good night vision. Maybe so, but in hundreds of séances involving thousands of sitters, the odds are that some of the sitters would have exceptional night vision also. And it would only take one such sitter to blow the whistle on the enterprise.
It would seem, then, that taps delivered on command to specified targets in the dark are good evidence for paranormal activity. I was wrong to dismiss this category of evidence so cavalierly.