Frazier. The Main Branch was also used for major works and invention. Edwin Land conducted research at the building for his later invention, the Land Camera, while Chester Carlson invented Xerox photocopiers after researching photoconductivity and electrostatics at the library. During World War II, American soldiers decoded a Japanese cipher based on a Mexican phone book whose last remaining copy among Allied nations existed at the Main Branch. 1920s and 1930s Initially, the Main Branch was opened at 1 p.m. on Sundays and 9 a.m. on all other days, and it closed at 10 p.m. each day. This was to encourage patrons to use the new library. By 1926, the library was heavily patronized, with up to 1,000 people per hour requesting books. The library was most used between 10 a.m. to 12 p.m. and 3:30 to 5:50 p.m., and from October through May. The most highly requested books were those for economics and American and English literature, though during World War I geography books were the most demanded because of the ongoing war. It was estimated that 4million people per year used the Main Branch in 1928, up from 2million in 1918 and 3million in 1926. There were 1.3million books requested by nearly 600,000 people through call slips in 1927. By 1934, though annual patronage held steady at 4million visitors, the Main Branch had 3.61million volumes in its collection. Due to the increased demand for books, new shelves were installed in the stockrooms and the cellars by the 1920s to accommodate the expanded stacks. However, this still proved to be insufficient. The New York Public Library announced an expansion of the Main Branch in 1928. Thomas Hastings prepared plans for new wings near the north and south sides of the structure, which would extend eastward toward Fifth Avenue, as well as a storage annex in Bryant Park to the west. The expansion was planned to cost $2million, but was never built. After Hastings died in 1929, it was revealed that his will contained $100,000 for modifications to the facade, with which he had been dissatisfied. A theater collection was installed in the Main Reading Room in 1933. Two years later, the Bryant Park Open-Air Reading Room was established, operating during the summer. The reading room was meant to improve the morale of readers during the Great Depression, and it operated until 1943, when it closed down due to a