Designer: U.F. Grant (possibly), with improvements by Jack Hughes
The Chair Suspension may have been invented by U.F. Grant. Grant's version involved a long drape that hung over the board and could be flicked back slightly to show apparently nothing on the chair seat holding the board. Any chair could be used. Grant probably showed this method around 1940. It was not very deceptive (because of the long drape), so the modern chair version was developed. The modern version was invented by Jack Hughes. It's an illusion where a person floats in midair, supported only by the back of a fold-up chair.
A magician places two folding chairs facing each other. He then places a board across the top, bridging the two chairs. An assistant lies on top of the board, and the magician wraps them in cloth. He then removes one chair, leaving the board and the person suspended in the air supported only by the remaining chair. The magician finally removes the board itself, leaving the person suspended.
Photo Credit: Mak Magic (formerly UF Grant) - Shows modern version