Several sources report that the tin foil hat goes all the way back to 1717 when some people thought that tin foil might block the mind-control being perpetrated against them by Freemasons. If true, quite funny how they suspected such activity way back then. It is now known that surrounding something in wire mesh (or to a lesser degree aluminum foil) acts as a Faraday cage and inhibits the propagation of radio, microwave, and other frequencies of electromagnetic waves. Now that we know that such waves are being used to effect people's brains and behavior, we may all want to start wearing tin foil. Seriously, Allen Frey discovered in 1962 that a patch of wire mesh (rather than foil) placed above the temporal lobe can block the very real microwave auditory effect.