2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



to the altitude, and consequently the population continuously shifts. 

 Only high wages induce the men to live here, and as a rule they stay 

 only a few weeks, after which, with a little money, they leave for the 

 lower altitudes. Many of the men take their families with them, but 

 so far as is known no woman has given birth to a child at this altitude. 

 Most of the children in the camp were born in Ollague (12,000 ft.). 



The day after my arrival in camp, I set up the pyrheliometers and 

 ran a long series of observations here. The sky was very clear, with 

 only a few wisps of cirri visible. On my second day in camp I made 

 arrangements to go on up to the mine. Mules were available, and with 

 the help of one of the guides I got all the instruments roped on one 

 of the mules. We rode all the way to the top, and even with the 

 loads and our constant prodding the mules did not seem to suffer from 

 the height. Horses become so nervous that they cannot be used here. 



We arrived at the sulfur mine at about lo o'clock in the morning, 

 and there I found two boys to help me carry the instruments to the 

 top of the mine. There were no boxes or tables available to hold the 

 pyrheliometers, so I chose a ledge of ice covered with sulfur. Little 

 blocks of yellow sulfur served nicely to level up the legs of the 

 pyrheliometers. Below this was a sloping ledge of clear ice on which 

 I stood. I set up the theodolite on the ice ; the only trouble encountered 

 was that the ice would melt under the legs, and the instrument had 

 to be releveled each time a reading was taken. This was due partly 

 to the weight and partly to the fact that the brass points on the legs 

 were black and served as very good absorbers of the sun's rays. For- 

 tunately the sky here also was very clear, and there was no wind 

 during the observing. 



All readings were made with a stop watch whose second hand had 

 an eccentricity of less than i second as tested with a standard pendulum 

 used in our regular observations. A sun reflector was attached to the 

 back of the telescope for the solar altitudes. The constants of pyrheli- 

 ometers No. 29 and No. 30 were determined before and after the trip. 

 The silver disks were not touched during the journey. Before each 

 set of observations the three screws holding the silver disks were 

 loosened; after the observations they were again tightened. No severe 

 jar or bump was given the pyrheliometers throughout the trip. On 

 the return from the mine the theodolite box fell off the mule, but 

 before it could roll down the mountain, the muleteer jumped from 

 his mule and caught it. Fortunately no harm was done. 



The results of the instrumental data were not apparent to the senses. 

 At the mine even during the middle of the day the temperature hardly 

 rose above freezing, even though Aunconquilcha is nearly 200 miles 



