Smithsonian Report, 1948.—Abbot PLATE 6 
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1. SELF-RECORDING BALLOON PYRHELIOMETER, FLOWN TO AN ALTITUDE OF 
25 MILES IN 1914 
2. SOLAR-CONSTANT OBSERVATORY OF THE SMITHSONIAN INSTITUTION AT 
MOUNT ST. KATHERINE, EGYPT 
This is at an altitude of 8,500 feet. Spectrobolometer is within the tunnel, and sunlight is reflected in to it. 
