134 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 
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unit is the calorie. About thirty standardized silver disk pyrheli- 
ometers have been sent out by the Smithsonian Institution at cost, so 
that this same scale of measurement is now available in many 
countries, including Canada, United States, Mexico, Peru, Brazil, 
Argentina, Philippines, Java, Teneriffe, Spain, Italy, France, Eng- 
land, Germany, and Switzerland. 
A new instrument, the ‘ pyranometer,” adopted for measuring the 
brightness either of the sun alone, the sun and sky, the sky alone, 
or the nocturnal radiation of a blackened surface to the whole sky, 
has been perfected and was much used at Mount Wilson in 1916. 
This instrument is suitable for measuring the intensity of light where 
plants grow, whether in full sunlight or deep shade. Its results 
agree accurately with the standard scale of radiation mentioned 
above. 
