Thomas Jefferson came up with the idea of a portable writing desk during his 200 mile coach rides between his home at Monticello, Virginia and the Continental Congress in Philadelphia, Pennsylvania.
He designed this desk, with an adjustable book rest and a locking drawer. He gave the drawings to Philadelphia cabinet maker Benjamin Randolph to build.
The Declaration of Independence was written on this "lap box."
The original lap desk is on display at the Smithsonian Institution in Washington DC.