Ministry of Home Security Research and Experiments Department - Bulletin No. B13, Notes On Aerial Observation At Night. P/b, 18 x 24cm. 16p, dated January 1943. Written to help people 'not yet experienced in night observation to know what to expect and what to allow for'. Covers vision and recognition, how familiarity helps recognition, the principles of night vision and how at least 20 minutes is needed for effective dark adaption. Also covers visibility of the ground at night, visibility of other aircraft and the moon and moon phases. Also has hints on better vision - take care to be familiar with the target area beforehand, keep goggles and perspex clean and unscratched, avoid bright lights, use night binoculars for checking ground detail and so on. Cover is soiled, some loose pages. Some torn/damaged pages that would benefit from archival tape repairs. Interesting but a bit tatty. Stock code P21089.