The periscope . can be used as a backup display for manual attitude control, and also to determine the capsulea#39;s E? 90aquot; A l / View 01 Qa Yow Fig. 2. a Cape ... The window is phase polarized along the horizontal axis by means of a polaroid filter. [Reduction of light ... about 20 to 25 per cent. DONALD L. ZINK june l963a189.