96 THE NEW WORLD OF SCIENCE 



or mosaic maps would be grossly uneven at the junction of their 

 constituent prints. 



Here, as in many other cases, the severe requirements set by 

 this new form of photography led to intensive study, resulting 

 in detail improvements which have reacted to the advancement 

 of photography as a whole. Improved designs were worked 

 out, in particular one by the American Air Service, which 

 resulted in giving speed and regulation of speed much beyond 

 anything heretofore attained. 



The sensitive plate is, of course, the crux of the photographic 

 problem. Needless to say, high speed is essential in aerial 

 work. Careful research developed, however, that mere speed, 

 as ordinarily measured, is not alone sufficient. Aerial views 

 are apt to be much under-exposed, and in addition there is but 

 small contrast of brightness in objects on the haze-covered 

 earth. Consequently it is desirable to have a photographic 

 emulsion that will develop as much contrast as possible, with 

 short exposures a combination of qualities not usually found. 



In addition to speed and contrast requirements comes the 

 very important one of color sensitiveness. Photography from 

 high altitudes means photography through a thick layer of aerial 

 haze. Because of its general bluish color, this haze appears 

 much thicker to the blue-sensitive photographic plate than it is 

 to the naked eye. To pierce this haze it is imperative to use 

 color filters of a general yellow hue, and with these it is neces- 

 sary to employ plates sensitive to green, yellow and red. The 

 Germans used very generally a plate of extraordinary green 

 sensitiveness, greatly superior in that respect to anything pro- 

 duced by the French or the English. This plate one of the 

 American manufacturers was able to match and indeed to sur- 

 pass, thus producing what was undoubtedly the best orthochro- 

 matic plate used in the war. 



Probably the greatest achievement in photographic plate 

 making during the period of the war was the production of a 

 new panchromatic (sensitive to all colors) plate by one of the 

 English manufacturers, using new sensitizers developed by 



