In medieval times, the ducking stool was meant to establish whether a suspect was a witch. It consisted of a strongly made wooden armchair in which the offender was tied and ducked into water. If the "witch" sank she was deemed innocent. If she survived the immersion it was deemed that she was in league with the devil, meaning that she had rejected the "baptismal water” and was thus burned in fire as a witch.
In the 17th century it became a method of punishment for women accused of prostitution or scold.