On this day, a mining tradition dating back to 1911 ended: the use of canaries in coal mines to detect carbon monoxide and other toxic gases before they hurt humans. The idea of using canaries is credited to John Scott Haldane, known to some as “the father of oxygen therapy.” He suggested using a sentinel species: an animal more sensitive to the colorless, odorless carbon monoxide and other poisonous gases than humans. If the animal became ill or died, that would give miners a warning to evacuate.