An inventor and an environmentalist, Mary Walton helped tame pollution during the Industrial Revolution. In 1879, she patented a system for pumping air through water tanks to help trap pollutants, which significantly reduced air pollution in Manhattan. Walton continued her crusade to make the city more livable by tackling noise pollution caused by the elevated trains. Using a model train set in her basement, she experimented with multiple noise reduction techniques before discovering that a wood track casing filled with tar, sand and cotton significantly helped muffle the sound. In 1881, she acquired a patent for the track, which she later sold to the New York City Metropolitan Railroad.