History of the United States Patent Office
On April 10, 1790, having been previously passed by both houses, the first Patent Act became law after being signed by President George Washington. The law was entitled: "An Act to Promote the Progress of Useful Arts." The full text of this Act may be found at Wikisource. The passage of this Act by Congress was authorized by Article I Section 8 of the US Constitution, which said, in part:

The Congress shall have Power To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.

History of the United States Patent Office.
The Patent Office Pony