36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 7I 



Institution for the purpose of measuring radiation of various kinds. 

 At Hump Mountain, measurements were made on the intensity of 

 radiation from the sky, clear, hazy, cloudy, and foggy ; the radiation 

 under trees, plants, etc., snow reflection radiation, etc. In May, 1918, 

 the instrument was taken to Calama, Chile, and other sky radiation 

 measurements have been made there. 



The pyranometer measures radiation by means of a delicate elec- 

 tric thermo-couple, which is heated by blackened manganin strips 

 on which the radiation falls. The instrument is calibrated by means 

 of a solar comparison with the pyrheliometer. The " constant ■' of 

 the instrument is found to vary but little during long intervals. 



Observations were made which showed that the pyranometer is a 

 very sensitive instrument if joined to a "delicate galvanometer, such 

 as is used in bolometric work. The " holograph " made with the 

 pyranometer showed that it registers all wave lengths from 2.2/x to 

 0.33/A in their proper magnitude. 



A table is given showing the relative intensity of the radiation 

 from the whole sky (at air masses from 5.00 to 1.25) as compared 

 with the simultaneous intensity of the solar beam as measured by 

 the pyrheliometer, the latter being reduced to a horizontal surface. 

 Intensities of total sky radiation for rather hazy though cloudless 

 skies is given for air masses 3 and 2 for Calama, Chile. 



The radiation from three horizontal zones of 30° width each, was 

 investigated, during varying sky conditions. Also the intensity in 

 various azimuths of the sky with a circular zone of 60° diameter. 

 The position of the sun was taken as zero azimuth for each set and 

 the other azimuths as well as the zenith region compared with it. 



Observations were made on cloudy and foggy skies, and the in- 

 tensity on a horizontal surface compared with the solar and clear 

 sky radiation falling on. a horizontal surface. 



A brief investigation was made of a comparison of the radiation 

 from a hillside covered with dry grass and weeds, and comparing 

 it with an equal area of clear zenith sky. 



Investigations were made both at Hump Mountain and Calama. 

 regarding the diminution of radiation at dusk, and comparing it 

 with solar intensity. 



Observations were made of the intensity of radiation under trees 

 and plants, showing roughly the amount of radiation needed by 

 various plant growths. 



Limited observations were made of the intensity of radiation re- 

 flected by snow, and comparing it with solar and sky radiation 

 occurring at the time. 



