edison's ghost detector

So it turns out that Thomas Edison believed in ghosts, enough so that he developed an experiment to test his hypothesis that "spiritual entities ... should have some of the attributes of ordinary matter." To test this view, he set up a basic motion detector, figuring if there was a ghost present, it would trip the beam:

In a darkened room in his great laboratory, surrounded with beakers, generators, and other experimental equipment, Edison set up a photo-electric cell. A tiny pencil of light, coming from a powerful lamp, bored through the darkness and struck the active surface of this cell, where it was transformed instantly into a feeble electric current. Any object, no matter how thin, transparent or small, would cause a registration on the cell if it cut through the beam. ...

Tense hours were spent watching the delicate instruments for the slightest indication of a spirit form, but none came. The wind howled around the corners of the laboratory building, the spiritualists exorcised, but the ghosts, if any, remained in their abode in eternity. Narrowed scientific eyes saw the meter’s needle remain steady as a rock. ...

The great inventor was a realist and his experiment revealed the stony silence his profound mind expected to find. If spiritual entities existed Edison believed that they should have some of the attributes of ordinary matter. Hence his belief that if spirits existed they could be detected by the electric eye.

Of course, he detected nothing and thus assumed not that his hypothesis was wrong, but instead that ghosts did not exist. A safe assumption, some might say, but we'd offer our own hypothesis as an example of how his experiment might have been a bit too limiting. His tale -- taken from Modern Mechanix issue 10 (1933), and recounted in full at the Modern Mechanix blog -- will be worth keeping in mind as we conduct our own experiments. And maybe 85 years from now, there will be someone pointing out how wrong were our own theories...