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: $M\alpha$ of platinum (6A); $K\alpha$ of aluminum (8.3A); $L\alpha$ of copper (13.3A); $L\alpha$ of iron (17.7A); $L\alpha$ of chromium (21.5A); $K\alpha$ 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 $L\alpha$ of copper and also directly by calculation from the constants of the spectrometer.