134 SMITHSONIAN MISCELLANEOUS COLLECTIONS \0L. 66 



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, Teneritfe, 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. 



