Closely associated with the colour is the polarization of the light from the sky.
In other directions the polarization becomes less and less complete as we approach the vertical.
Of this nature are the neutral points, where the polarization changes character, observed by F.
On the other hand, that the direction of complete polarization should be independent of the refracting power of the matter composing the cloud has been considered mysterious.
It must be noticed, however, that the angle of maximum polarization would be about 76° instead of 90°.