Abraham Lincoln's patent relates to an invention to buoy and lift boats over shoals and obstructions in a river. Abraham Lincoln conceived the invention when on two occasions the boat on which he traveled got hung up on obstructions. Lincoln's device was composed of large bellows attached to the sides of a boat that were expandable due to air chambers. Filed on March 10, 1849, Lincoln's patent was issued as Patent No. 6,469 later that year, on May 22. His successful patent application led to his drafting and delivering two lectures on the subject of patents while he was president.