]62 ANNUAL REPOET SMITHSONIAN INSTITUTION, 193 3 



sistance thermometer, for thi3 purpose about the year 1880. We 

 use the bolometer every day in our three field stations on high 

 desert mountains of California, Chile, and Egypt to measure the 

 energy of the rays that compose the sun's spectrum, 



A STATION FOR OBSERVING SOLAR RADIATION 



Plate 4, figure 1 shows our station at Montezuma, Chile. It occu- 

 pies a foothill 9,000 feet in height not far from the Andes Moun- 

 tain^, which rise to 18,000 feet within full view. The station is near 

 the nitrate fields of northern Chile, where neither beast nor bird, 

 reptile nor insect, nor any living plant is to be seen. Darwin, in 

 his book entitled " The Voyage of the Beagle ", tells of riding all 

 day in this Desert of Atacama, and seeing no life except a few 

 flies feasting on the dead body of a mule. The observers bring all 

 the water for washing, bathing, cooking, and photography from 

 Calama, a town 10 miles away. They have a piano, Victrola, radio, 

 books and games, and telephonic communication with Calama, but 

 the life there ig certainly not a gay one. Every day that is fair 

 (and 80 percent of the days are fair) they observe from about 6 

 o'clock until 10 o'clock a.m., and compute from 10 o'clock until mid- 

 afternoon, or even later. By evening they are able to telephone out 

 their message, giving the intensity of the sun's rays as they would 

 be found outside our atmosphere. The result reaches Washington 

 early on the next morning and is broadcast by Science Service at 

 4 p.m. to the world. 



Plate 4, figure 2 shows the bleak character of our newly occupied 

 station in the Sinai Peninsula, Egypt. It is on Mount St. Katherine, 

 8,500 feet in elevation, about 10 miles from St. Katherine Monastery 

 on Mount Sinai. The director, Mr. Zodtner, his wife, and two small 

 children, and the assistant, Mr. Greeley, occupy this station. 



SOLAR ENERGY SPECTRA 



Figure 6 shows a series of bolometric solar spectral energy curves 

 all obtained on the same forenoon at our station at Montezuma, 

 Chile. You will note first of all that the spectrum visible to the eye 

 makes less than half of the length of the prismatic solar energy 

 spectrum as we observe it. Second, you will observe that at several 

 places in the infrared region there are great vacancies where the 

 spectral energy almost disappears. These bands, named by Langley 

 p, ^, ij/, and n, are produced by the absorption of the sun's rays by 

 water vapor in the earth's atmosphere. Third, you will see many 

 smaller indentations in the visible and ultraviolet regions, which 

 are duplicated on all of the several energy curves shown in the figure. 

 These indentations correspond to the dark lines called Fraunhofer 

 lines seen visually in, or in photographs of, spectra of the sun. 



