The Fox Sisters
The Fox sisters (Margaretta and Kate/Cathie) caused a sensation in the late 1840s, when the news broke that they could communicate with a spirit in their home in Hydesville, NY. The "spirit" communicated through rapping sounds (e.g., two raps for yes). The sisters went on to become professional mediums, and were instrumental in founding the spiritualist movement. Later in their lives the sisters admitted to faking the spirit raps (many researchers had been insisting all along that the noises were faked), but at least one of them took back the confession before she died. Despite this, the Fox sisters are generally considered frauds.
Other web pages about the Fox Sisters:
The Fox Sisters and the Birth of Spiritualism
Who2 Profile: The Fox Sisters
Fox Sisters, the Columbia Encyclopedia
Modern Spiritualism: The Fox Sisters and the "Rochester Rappings"
This page (http://www.ghosts.org/ghpics/foxsis.html) last updated April 2, 2005.