Joseph Priestley, an English scientist and clergyman, is credited with discovering oxygen in 1774. However, it wasn't until the development of a practical oxygen tank by Henry Fleuss in 1879 that humans could benefit from the use of breathable oxygen. His apparatus consisted of a metal flask containing compressed oxygen connected to a mask covering the wearer's face. This invention eventually paved the way for the use of scuba diving as well as medical applications of oxygen.