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The absorption of radiation of wavelength between 240 A and 1000 A in helium and argon was measured photometrically in a grazing incidence vacuum spectrograph. For helium a sharp absorption edge was observed at 504. 3 A. Near this edge the photoionization cross section at 495. 7 A was found to be 6. 9510^-18 cm^2. The variation of the cross section as a function of the wavelength was in agreement with the computed curves by Wheeler and Vinti within the experimental error limit. For argon three absorption edges exist at 786. 8 A, 778. 0 A, and 424. 0 A corresponding to the M₃, M₂, and M₁ edges, respectively. Possible autoionization phenomena between the M₂ and M₃ edges were observed. The cross section at the M₂ edge was found to be 3. 510^-17 cm^2 which is comparable with the value computed by Dalgarno.
Lee et al. (1955) studied this question.