Root, a pupil at Cornelius' studio. Root published The Camera and The Pencil which provided background on the roots of photography in the United States. The book was highlighted at the Centennial Exhibition in Philadelphia in 1876 and caught the attention of Julius Sachse, a noted Philadelphia photographer and future editor of American Journal of Photography. Sachse began interviewing Cornelius and other members of the American Philosophical Society in order to record the history of photography in the United States correctly. Cornelius told Sachse that he began taking photographs in October 1839 but no evidence was found of his claim until 1975 when a librarian at the American Philosophical Society discovered photographs taken by Cornelius dated in 1839. Later work Cornelius operated two of the earliest photographic studios in the United States between 1841 and 1843. His studio achieved improved photographic quality through the implementation of reflectors to direct additional light onto the portrait subject and blue glass filters. These changes along with improved photographic plates allowed portrait subject to only have to remain still for about one minute. His studio became popular with wealthy patrons and many of his portraits of famous people still exist. As the popularity of photography grew and more photographers opened studios, Cornelius either lost interest or realized that he could make more money at the family gas and lighting company. He managed Cornelius & Co. (later known as Cornelius & Baker) and had great success with his invention of the "solar lamp". At the time, whale-oil was used in lamps but had become very expensive. Cornelius revised a British lamp design which forced additional air into the burner and allowed for the burning of lard rather than whale oil. He applied for and received a U.S. patent for the "solar lamp" in 1843. The lamp proved extremely popular and was sold in the U.S. and Europe. Two large factories in Philadelphia manufactured the lamp. Cornelius also received patents for lighting gaslights with electric sparks. The Cornelius lamp company also created the first kerosene lamp, however cheaper and more efficient versions dominated the market. While Cornelius was still a wealthy man, his once dominant lamp company was overtaken by other companies. Personal life Cornelius married Harriet Comly (sometimes spelled "Comely") in 1832. They had eight children: three sons and five daughters. Cornelius retired from his family's business in 1877. In his later years, he lived