X-Rays of Long Wave-Length from a Ruled Grating

By the use of a grating ruled on glass (200 lines per millimeter) at grazing incidence (20{'} to 40{'}) in vacuum, the following lines have been obtained: Mα of platinum (6A); Kα of aluminum (8.3A); Lα of copper (13.3A); Lα of iron (17.7A); Lα of chromium (21.5A); Kα of carbon (45.8A). A water-cooled metal x-ray tube with hot lime-coated platinum cathode was used. This was connected directly to the spectrometer with no absorbing film between the anticathode and the photographic plate. Wave-lengths were determined with reference to Lα of copper and also directly by calculation from the constants of the spectrometer.