This is about how people look for the cause of a spooky feeling. Reports of hauntings include seeing a figure, odd smells, sudden changes in temperature and a strong sense of presence. The Society for Psychical Research was founded in London in 1882 to study such reports with care. The questions are what made the feeling, and where in the room it happened.
A scientist named Vic Tandy traced eerie feelings in a lab to a faulty extractor fan that made very low sound. He also left a fencing blade clamped in a vice in the lab. It was found vibrating up and down, a sign that something in the room was shaking it. His case shows one way to deal with a strange feeling in a room: look for a cause that can be found and checked.
The fan made very low sound, which brings up a word worth knowing: infrasound. People generally hear sounds between 20 and 20,000 hertz, and infrasound is sound with a pitch below that range. Pitch is how high or low a sound is. Infrasound can be sensed if it is strong enough, mostly by the ear.
Other scientists tried another way to check a place. Scientists in England and Scotland asked visitors to walk around places with a haunted reputation and mark where they felt anything unusual. The marks can be compared and looked at again, which is what makes them useful to someone testing an idea.
A house can make plenty of ordinary sounds on its own. Houses make creaks and pops, and wood floors and pipes make them. Wood, metal and glass get a tiny bit bigger when they warm up and a tiny bit smaller when they cool down. Metal air ducts can pop when they warm up. Each of these is a small, ordinary thing that a person can check.
The seasons matter as well, because winter air dries wood out, so the boards shrink. That is why some floors make more noise in cold weather. A draft is moving air that slips in through gaps around windows and doors, which a person can feel and check. A scientist would test each of these ideas one at a time, to see which one fits the room.
The brain adds tricks of its own. People see faces in clouds, rocks and tree bark, because our brains are very good at spotting faces. The brain area that notices faces gets busy when we only think we see a face, like one in a cloud. Seeing faces in things that have no faces has a name: pareidolia.
A hill on Mars shows how a first look can mislead. In one old photo, it looked like a face, and the reason was shadows. Sharper photos later showed that it is just a hill, and there are dozens of hills like it nearby. A better photo is a test that the first impression has to pass.
Some tricks are built on purpose. On a stage long ago, people made a see-through ghost with a sheet of glass and a hidden actor in bright light. The trick is called Pepper's ghost. A big angled pane of glass lets the audience see the actor's reflection on the stage. John Henry Pepper ran the Royal Polytechnic in London, and in 1862 he turned Henry Dircks's idea into a stage effect.
Words to know
- infrasound: very low sound
- pareidolia: seeing faces
- reflection: mirrored picture
- ducts: air tubes
