INTRODUCTION Whenever Dr. Samuel Johnson (1709–1784), the English lexicographer, critic, and author, walked down a street he touched every wooden post he passed. He also stepped out of a door with his right foot first, and avoided all the cracks between paving stones. He believed that if he didn’t, something unpleasant would happen. Niels Bohr, the famous physicist, had a horseshoe hanging above his office door. “Surely you don’t believe that will make any difference to your luck?” a colleague asked. “No,” agreed Niels, “but I hear it works even for those who don’t believe.” Sir Winston Churchill always carried a “lucky” walking stick when he had to travel on a Friday, a day he felt was unlucky. He refused to travel at all on Friday the 13th. He also touched any black cats he came across, as he considered them lucky. Alfred Gwynne Vanderbilt slept in a bed that had all four legs resting in dishes of salt, in order to protect himself from evil spirits. Many years ago, a friend of mine deliberately performed a sequence of events on Friday the 13th, in an attempt to disprove the effects of superstitions. He deliberately spilt salt, walked on all the cracks in the sidewalk he could, had the landlord’s black cat cross his path, signed a lease agreement, and then walked under a ladder. The next day, his girlfriend left him. People are as superstitious today as they have ever been. Have you ever knocked on wood or walked around a ladder? Are you happy when you see a pin and pick it up, because ix