GREAT WALL OF PERU SHIPPEE 467 



elaborate fortifications — fortified hills and defensive walls of various 

 sorts — but also with the remains of cities, towns, and extensive irriga- 

 tion works. Only when one looks down upon the wall from the air 

 and thus is able to see long sections of it can one realize that it is a 

 feature quite distinct from the short sections of wall characteristic of 

 the Santa delta. This broad view presented to observer and camera 

 is what makes the airplane so important an instrument in modem 

 exploration. The aerial observer is afforded, and the aerial camera 

 records frequently in a single exposure, a synthesis of details whose 

 relationships might otherwise never be discovered. 



SURVEYS OF CHAN-CHAN AND PAGHAGAMAC 



The base at Trujillo from wdiich we made our first flight over the 

 Great Wall had been established for the purpose of making a mosaic 

 map of the ruins of Chan-Chan, the capital of the kingdom of the 

 Great Chimii whom the Incas conquered shortly before the Spanish 

 conquest. The ruins have recently been described by Maj. Otto 

 Holstein in an article in the Geographical Review. He particularly 

 called attention to the disastrous effect of the rains of 1925 and urged 

 that systematic study of the site be made without delay.' Johnson 

 had had it in mind for some time to make an accurate record of these 

 ruins, based on a good triangulation, before another rainy year like 

 that of 1925 had completed their destruction. 



The ruins occupy an area of about 11 square miles. From a base 

 line of 3,600 feet two of us wdth a detail of soldiers lent us by the 

 Trujillo garrison triangulated the entire area and laid white lime 

 markers. It was difficult to w^ork with any speed and still obtain the 

 degree of accuracy for wdiich we were striving, for the high adobe 

 walls and the rounded bulks of the huacas so interfered with the 

 sights that we had to choose all points with great care. Three and a 

 half days were required for the completion of the triangulation. 



On the other hand, in 40 minutes from the time the plane took off 

 for the aerial survey the wheels again touched ground with the sur- 

 vey completed. Furthermore, w^ien we came to the assembling 

 of the mosaic, we found that the only corrections our photographs 

 needed were those required to offset the slight variations in the alti- 

 tude of the plane while the photographs were being made — variations 

 due to the airplane rising or settling in updrafts and downdrafts. 

 In nine cases out of ten the accuracy of an aerial survey of such a 

 small area made in a country as flat as the site of Chan-Chan would 

 be sufficient without ground control. 



' Holstein, Otto, Chan-Chan : Capital of the Great Chimfi, Geogr. Rev., vol. 17, pp. 

 36-Gl, 1927. 



149571—33 31 



