386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



flight of 1935 shown on plate 9 are examples of photographs useful 

 in recording an event. 



Oblique photographs give a view very similar to that which we 

 ordinarily observe as we walk about in a flat field, except that a 

 great deal more is included in the view. As we increase the elevation 

 from which we look at the landscape, its aspect changes and the 

 silhouette of hills and other forms of relief against the horizon 

 disappear. Instead of seeing the hill ahead of us, we are more 

 impressed by the rivers, farms, woods, and cities which from lower 

 altitudes of observation are hidden. The camera brings back a 

 record of what we see, and as the height from which the pictures 

 are taken is increased, the area included in the picture increases, also 

 the things hidden by relief become less. The area covered in any 

 single obliqme from high altitude is very large. Features such as 

 roads, railroads, woods, streams, cities, and cultivated fields show up 

 distinctly. A little study will also give a fair idea of relief, which 

 is indicated by the drainage and by shadows. However, it is easy 

 to be deceived by the relief actually present when one is studying 

 an oblique picture even though it is more clearly indicated in this 

 kind of picture than in the vertical. Stereoscopic pairs of either 

 obliques or verticals are far superior tp single pictures for a detailed 

 study. Besides showing many things which would not ordinarily be 

 observed from an airplane, photographs show features which are not 

 visible to the eye. This is partly because the resolving power of 

 the camera lens is much greater than that of the eye, as is well borne 

 out by photographs taken during the 1934 and 1935 stratosphere 

 flights and by statements of members of the crews of those balloons. 

 Captain Anderson tells me that when at an altitude of about 60,000 

 feet over northwestern Nebraska he had great difficulty in locating 

 a railroad shown on the map, the position of which was accurately 

 known by him. He finally succeeded in locating it visually by being 

 able to see some cuts through which it ran, although he was unable 

 to see the railroad itself. He also found that farm buildings were 

 invisible, although the different fields and pastures, as well as the 

 smaller plots in which the farm buildings were located, could easily 

 be seen. These railroads and farm buildings are visible on pictures 

 taken from the balloon while at or near its maximum altitude. This 

 is in keeping with observation from much lower altitudes. In the 

 training of airplane observers for the control of artillery fire, puff 

 targets are used. These are moved about by the men of the ground 

 crew which operate them, and the men can be seen moving around 

 with the puff targets when flying at less than 4,000 feet above them 

 but are invisible from higher altitudes. 



