In the early days of the US patent office, the pace of innovation was sufficiently slow that patents were signed by George Washington and Thomas Jefferson themselves. But pretty soon, Americans were inventing all manner of cool stuff and sending in patent forms. In the first 46 years, about 10,000 patents were issued, but here’s the thing: They were all lost when the patent office burned down in 1836. They’re now known as the “X-patents”, and every once in a while one of them comes to light.

Two lawyers recently struck the motherlode, when two lawyers discovered a clue that led them to finding copies of 14 of the X-patents. That includes the original patent for the internal combustion engine! (That’s a picture of them above from the New York Times, with a replica of the engine.)