Pressure broadening by foreign gases has been treated in a previous communication on the basis of a statistical analysis of the van der Waals interaction curves. It is now shown that this statistical analysis must necessarily lead to the same result as the more common, but less perspicuous, procedure of expanding the modulated frequencies in a Fourier integral. There is no collision broadening which is not included in the effect previously discussed.—The effect of light modulations by the momentary screening action of absorbing particles is considered.—Extending the former results, we have calculated the distribution of frequencies within a spectral line broadened by foreign pressures, obtaining an approximate closed expression, and an accurate function which can be evaluated graphically. Agreement with experiment on the Hg line 2537A is good, though not entirely unambiguous because of some lack of certainty of the molecular constants of attraction. More significant, perhaps, is the fact that it is possible now to determine the latter from an analysis of the line contour.

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