GREAT WALL OF PERU — SHIPPEE 471 



on the high pampa, so-called, back of the coast range between Are- 

 quipa and Mollendo for a brief examination of the famous La Joya 

 crescentic sand dunes (pi. 8, fig. 2) — dunes that move an average of 

 60 feet a year and cover the pampas as far south as Tacna. 



We also made a preliminary examination from the air of the Colca 

 Valley, some 70 miles north of Arequipa, where 14 " lost " villages 

 nestle on the floor of a steep gorge. Apparently thej^ had long since 

 been all but forgotten until Johnson photographed them on a flight 

 made in 1929 when he was cliief photographer of the Peruvian Naval 

 Air Force. 



In fact, a desire to revisit and study this valley was our first pur- 

 pose in organizing the expedition. After our return from Cuzco 

 a land party spent six weeks in the valley, a landing field was con- 

 structed, and the whole upper valley was surveyed from the air. 

 The work in the Colca Valley with that in the near-by Andagua 

 Valley, where some 40 small volcanoes, apparently hitherto unknown, 

 were located and photographed, will be related in another article 

 in the Geographical Keview. 



STATIC TESTS 



A brief account of our difliculties with static may be of use to 

 others doing photographic work under similar conditions. AVe found 

 on returning to our Lima laboratory after our work in the north that 

 a good many of the photographs taken at high altitudes were spoiled 

 by static. Streaks and lines crossed and recrossed many of the 

 negatives so as to make them valueless. This is an unsolved problem 

 of aerial photography. Static electricity is obviously the cause, but 

 the exact explanation of its presence and a remedy for its effect are 

 still being sought by photographic experts. It occurs most fre- 

 quently at high altitudes in rarefied air where static conditions reach 

 a maximum. The static reaches the inside of the aerial camera or is 

 generated there — as by the rapid unrolling of the films — and the 

 electrical sparks and flashes leave their image on the negative. 



Experiments in eliminating this phenomenon have been made in 

 the United States, in Canada, and in Europe, not only in commercial 

 organizations but also by Government research laboratories. Prog- 

 ress in this experimentation is greatly retarded by the fact that 

 static conditions can not be accurately reproduced in the laboratory 

 but must be encountered in the air. On some flights roll after roll 

 of aerial film may be exposed with no trace of static. Then on the 

 very next flight dozens of photographs will show its effect. 



Although we failed to eliminate the static, we did learn enough 

 about the conditions under which it was most prevalent to cut down 

 materially the number of wasted exposures. Equipped with oxygen 



