From the spectral intensity distribution of solar X-radiation one can conclude that there is a non-thermal contribution, which is effective during the initial phase of a flare. It is reasonable to suppose that the electrons producing the non-thermal radiation have a non-isotropic velocity distribution. Indeed, one should assume that the electrons, during their acceleration, obtain a preferred direction and that only afterwards does their velocity distribution become Maxwellian by means of collisions. Hence the short-wavelength continuous X-radiation in the initial phase of a flare, consisting mainly of bremsstrahlung, should be polarized and should have a non-isotropic angular distribution.

In papers presented to the IAU-Symposia in Budapest 1967 (Elwert, 1968) and in Leningrad last May, the polarization of X-radiation from electrons of a few keV accelerated in solar flares has been calculated using energy distributions based on the observations of Pounds et al. obtained with the satellites Ariel I and OSO-4.