On the Absence of Absorption of Light in Interplanetary Space.

(Harlow Shapley. Studies of magnitudes in star clusters. V. Further evidence of the absence of scattering of light in space. Proceed. of the national Akademy of Sciences. Vol. 3. Numb. 3, p. 267—1917).

The importance of a quantitative study of the phenomena of the diffraction of light in interplanetary space for elucidating the properties of the cosmic medium in which light propagates was pointed out in particular by Kapteyn’s works. In Shapley’s first communication (Proceed. 2, 1916) it was shown that the selective absorption which might be attributed to the interstellar medium, and which ought to increase for shorter waves, cannot be established

...to explain. The systematic increase in the absorption of the more refrangible rays in the central parts of the stellar cluster the author attributes, in the present work, to the phenomenon of diffraction in the region of the stellar cluster when light passes through it. The numerous data presented by Shapley show that selective absorption of the short rays with increasing distance of the stars cannot be established and that, consequently, the interplanetary medium contains no appreciable amount of matter.

P. Lazarev.