92 THE NEW WORLD OF SCIENCE 



experiment, aerial photography grew to be one of the main 

 activities of the air forces. The war had not been in progress 

 a year before the aerial photograph was the indispensable guide 

 to all military operations. Enemy lines were completely photo- 

 graphed each day or even oftener. Negatives to the number 

 of scores of thousands were made every month by the Allied 

 armies, and from these, toward the end, half a million prints (in 

 round numbers) were distributed each week to intelligence offi- 

 cers, to artillery headquarters, even to infantry company com- 

 manders to guide them in their local operations. So searching 

 indeed did aerial photography become that as the war drew to a 

 close all troop movements had to be made at night or under 

 cover of bad weather. Elaborate attempts to camouflage bat- 

 teries and fixed structures against the eye of the camera were 

 met by the development of a corps of experts in a new art, the 

 interpretation of aerial photographs. 



The technical problems to be solved in the development of 

 photography from the air were numerous. 1 Practically every 

 resource of scientific photography had to be pressed into service 

 and carried to further development by intensive research before 

 aerial photographs with the necessary quality were procurable. 

 As might be surmised, the foremost problems to be met were 

 those introduced by the altitude, the speed, and the vibration 

 of the new camera platform. The great altitudes reached by 

 army reconnaissance flying 18,000 to 20,000 feet brought 

 demands for lenses of very long focus and for combinations 

 of sensitive plate and color filter to pierce the layer of haze 

 almost always present on the earth's surface. The speed of the 

 battle plane, sometimes as high as 150 miles an hour, when 

 considered with respect to the earth, demanded lenses of large 

 aperture and shutters capable of giving extremely short ex- 

 posures in order to prevent blurring due to the motion of the 

 image. The vibration from the engine necessitated not only 



1 For a comprehensive account of the technical aspects of aerial 

 photography see "Airplane Photography," by the present writer, pub- 

 lished by J. B. Lippincott & Co. 



