WAR-TIME PHOTOGRAPHY 101 



interpretation. At the best of times the vertical view presents 

 all objects in an unfamiliar aspect, while in modern warfare 

 the arts of camouflage are enlisted to render interpretation 

 harder yet. In aerial photography the greatest foes to camou- 

 flage are stereoscopic pictures, and the fact that the photo- 

 graphic plate is differently sensitive to colors than is the human 

 eye. Thus often gun coverings and concealed dugouts, not 

 noticeable by the observer as he flies over, show clearly in 

 the photograph he brings back, since the camouflage paint is a 

 visual but not a photographic match with its surroundings. 

 Camouflaging pigments had, therefore, to be tested photo- 

 graphically, and in turn plates and color filters were sought 

 which would defeat the efforts of the enemy camoufleur. 



The every day problem of the interpreter of photographs was 

 to detect changes of any sort the substitution of artificial 

 trees with concealed listening posts for real trees ; the removal 

 of sod to be used elsewhere for camouflage. For this purpose 

 photographs made on different days were laboriously compared, 

 side by side. Even when this was done, minute but important 

 changes would be missed, a common failure which led to several 

 proposals to facilitate such comparisons. One was the use of 

 the " blink microscope " in which the two pictures were viewed 

 successively in the same position, any change showing as a flut- 

 tering or blinking in the scene. In another ingenious scheme, 

 adapted from the astronomical method of searching for moving 

 asteroids, a positive made from one negative is laid over a nega- 

 tive of the same subject made at another time. If no change 

 has taken place the two merge to a neutral gray. If any- 

 thing in the view has moved, it stands out in striking contrast 

 with the undisturbed parts. 



In this brief sketch of war-time photography chief emphasis 

 has been laid on the contribution of photography to the winning 

 of the war. Reciprocally the demands of war have worked to 

 advance to no inconsiderable degree the science of photography. 

 This will be manifested, if in no other way, in the production 

 of photographic apparatus of greater accuracy and reliability 



