The Cumulative Index to National Geographic Magazine from 1899 to 1940 is a valuable reference book published by the National Geographic Society in 1941. This original hardcover book, written in English, indexes articles published in the magazine during this period. It is a comprehensive resource for collectors, researchers, and enthusiasts of National Geographic content, providing a detailed index of topics covered in the magazines from the turn of the 20th century to the year 1940.