Abstract
A concave glass grating of one meter radius of curvature with 30,000 lines to the inch has been selected to make quantitative measurements of grating efficiencies and reflecting powers between 200A and 1,000A. A water-cooled vacuum spark between tungsten electrodes made an extremely intense and sufficiently constant source. Small plane gratings were crossed with the concave grating so that the efficiency of the small grating could be determined for several wave-lengths and all angles of incidence. The results show that gratings which are efficient at normal incidence are not at all suitable near grazing incidence. The reflecting powers of glass and gold mirrors at 388A and 770A have been measured for all angles of incidence. The values of the reflecting power of glass for several angles of incidence and wave-lengths from 50A to 4800A are given. The influence of reflecting power, groove form, and surface smoothness on the efficiency of a grating are discussed.

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