122 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
of the station. We have been fortunate that these qualities have so 
seldom been lacking in our representatives there. 
Solar radiation, by being absorbed on black surfaces, is converted 
into heat. Its intensity is measured by its heating effect. The ob- 
servatories for measuring the solar constant of radiation have no 
telescopes. To insure constant temperature surroundings, highly fa- 
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upper set made between early morning and noon of a very dry day; the lower set simi- 
larly made on a moist though cloudless day. 
Figure 1.—Bolographic energy curves of the solar spectrum made at Montezuma, Chile. The 
vorable to exact measurements, they consist of horizontal tunnels 
about 10 feet wide and 7 feet high driven into the mountain some 40 
feet. We located the tunnels on a south slope in the Northern Hemi- 
sphere, and on a north slope in the Southern Hemisphere. Within the 
tunnel is installed a large prismatic spectroscope, whereby the sun ray 
reflected into the tunnel by the coelostat outside (shown in pl. 2) 
