Theory of the Concave Grating II Application of the Theory to the Off-Plane Eagle Mounting in a Vacuum Spectrograph*†

A recent treatment of concave grating theory is applied to an off-plane Eagle vacuum spectrograph, especially to that employing a grating of 21-foot radius and 30 000 lines/inch. Three tables and two graphs summarize the numerical calculations on the following factors: (1) change in wavelength from that calculated by the ordinary grating equation; (2) angle of slit rotation with respect to the grating rulings as a function of the angle of incidence; (3) optimum grating size as a function of the angle of incidence and spectral order; (4) resolving power in the 1250 to 2000-A region as affected by emulsion grain size, length of slit illumination, spectral order, and slit width. The calculations are found to be in reasonable agreement with experiment.