In 1902, Mary took a trip to New York City. She rode a streetcar on a blustery day and observed the driver's battle with the snow and sleet. He couldn't see through the windshield, so he frequently hopped outside to manually clear the glass. Needless to say, this was unpleasant for him as well as his passengers, who weren't thrilled about the chilly air or the delays.
Mary returned home and designed the first windshield wiper. It was a blade on the outside of the windshield that was controlled by a lever on the inside, keeping the driver safe and dry. In 1903, the US Patent & Trademark Office awarded Mary a patent for her device, but she was never able to sell the idea.
Luckily for us, Mary's invention was later revived and we're now able to provide windshield wipers to improve the safety of many transportation industries.