In modern astronomy we acquire fundamental knowledge concerning the dimensions and the constitution of the exterior layers of giant stars by the study of eclipsing systems. The red giants which form part of the systems of VV Cephei and ζ Aurigae have been studied thoroughly from the changes that the spectra of these systems undergo when the light of the bright eclipsed star passes through the envelope of the rarefied giant. At the present time it is clear that stars having extended envelopes are not rare. Thus, for example, F. I. Loukatskaya[1] (at the Principal Astronomical Observatory of the Academy of Sciences of the Ukrainian S.S.R.) has studied the eclipsing star AW Pegasi in different parts of the spectrum; she has shown that this star possesses a semi-transparent envelope that produces a considerable part of the eclipse. It turns out besides that certain spectral lines, observed in the spectrum of the bright star, come from the semi-transparent envelope of the less luminous companion.