Attempts have also been made to explain scientifically poltergeist disturbances that have not been traced to fraud or psychological factors. Skeptic and magician Milbourne Christopher found that some cases of poltergeist activity can be attributed to unusual air currents, such as a 1957 case on Cape Cod where downdrafts from an uncovered chimney became strong enough to blow a mirror off of a wall, overturn chairs and knock things off shelves.