In 1849, Abraham Lincoln patented a mechanism for lifting boats over obstacles on riverbeds. L: Matthew Brady; R: U.S. Patent Office / Abraham Lincoln

For a scientific take on President’s Day, we take a look back at those U.S. chief executives who made inventions -- a much shorter list than the number of presidents who practiced law.

More than half of U.S. presidents have been lawyers. That's the most common occupation for presidents, with military service at a distant second. The only U.S. president to hold a patent, at present, is Abraham Lincoln, who invented a mechanism for lifting boats over obstructions on riverbeds.

Lincoln’s invention, outlined in U.S. Patent No. 6469, consists of expandable buoyant chambers attached to the sides of a boat “to enable them to pass over bars, or through shallow water, without discharging their cargoes.” The chambers Lincoln designed are similar to bellows -- the instrument used to pump air into a dying fire -- and made of waterproof cloth.

Lincoln "was keenly interested in water transportation and canal building, and enthusiastically promoted both when he served in the Illinois legislature," Harry Rubenstein, a curator at the National Museum of American History, told Smithsonian Magazine in 2006.

Though the invention was never produced, and probably wasn’t practical, since you’d need a stupendous amount of force to stick the buoyant chambers down into the water, it’s still a fascinating artifact of history. A wooden model of the device whittled by Lincoln is on display in the Smithsonian.

The 16th president had even more experience with patents in his law career, which included stints as a patent attorney. Honest Abe was an ardent supporter of the patent system, saying that it "added the fuel of interest to the fire of genius," according to Rubenstein.

Though Lincoln is the only presidential patent holder, he wasn’t the only inventor to occupy the White House. Third president Thomas Jefferson was a born tinkerer as well. Jefferson’s wide-ranging inventiveness can be seen in the sheer breadth of things he made.

For instance, Jefferson constructed a wheel cipher consisting of 26 wooden wheels with the letters of the alphabet inscribed on the rims in a random order and stuck on a spindle. The device could be used to encode and decode messages and bears a striking similarity to a U.S. military device “reinvented” much later right before World War I.

Other inventions attributed to Jefferson include a macaroni machine, a swivel chair featuring a writing arm and leg rest, and a new type of iron plow. Jefferson also made lots of devices for his home at Monticello, including “magic” pairs of doors to his parlor -- when one opens or closes, the other automatically follows -- dumbwaiters to pull up bottles of wine from the cellar, and a clock outfitted with cannonball weights to keep track of days of the week and a Chinese gong to mark the hours. (The clock also had a face mounted on the exterior of the house, designed more for Jefferson’s slaves and other laborers to keep track of time; it features only an hour hand.)

And then there’s a presidential invention that’s a little more offbeat. According to Alec Foege, author of “The Tinkerers,” a history of inventors and do-it-your selfers, Jefferson successor James Madison devised a walking stick with a built-in microscope so you could look at tiny organisms on the ground without having to stoop too far.

“Unfortunately, [the walking stick] was too short for most men, other than the five-foot tall” Madison, Foege says.