132 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 2 



Orders for silver-disk pyrheliometers, built in our shops and cali- 

 brated against the Smithsonian standard pyrheliometer, have con- 

 tinued to come in. During the year five instruments were prepared 

 and sold at cost, as follows : 



S. I. No. 84 to Centre National de la Recherche Scientifique, Paris, France. 



S. I. No. 87 to Helsinki, Finland. 



S. I. No. 88 to Institute for Scientific Research, Central Africa. 



S. I. No. 89 to National Observatory of Athens, Greece. 



S. I. No. 90 to University of Rhode Island. 



As of now, a total of 89 silver-disk pyrheliometers have been fur- 

 nished by the Astrophysical Observatory to interested observatories 

 and institutions in many lands, thus making available throughout the 

 world the Smithsonian standard scale of radiation. In addition, five 

 Angstrom compensation pyrheliometers, modified in certain details as 

 experience has dictated, were built and calibrated. Three were sold 

 at cost to the Belgium Consulate General for use in the Belgian Congo. 



During the year certain electronic devices were procured as funds 

 permitted. These include a photopen recorder, Golay detector, and 

 electron multiplier photometer. Tests are in progress to determine 

 their most advantageous application to our special needs. 



For five years, 1926 to 1931, the Astrophysical Observatory occupied 

 Mount Brukkaros in Southwest Africa as a field observing station. 

 At the request of the Meteorological Service of South Africa, the 

 Smithsonian observations of total solar radiation during this period 

 on Mount Brukkaros were summarized and made available for publica- 

 tion in a new compendium of South African solar-radiation data. 



The Smithsonian standard water-flow pyrheliometer, against which 

 substandard comparisons were last made on Mount Wilson (Calif.) in 

 1947 by Dr. Abbot and Mr. Aldrich, has been overhauled and tested 

 by Mr. Hoover. It is planned to mount this standard instrument 

 at Table Mountain in the near future for a new series of comparisons 

 against our silver-disk substandards. 



An important study by Mr. Hoover is in progress, designed to clear 

 up certain elusive characteristics of the silver-disk pyrheliometer, 

 such as the cause of the temperature correction which it is found 

 necessary to apply. 



A special pyranometer was prepared for future testing at Table 

 Mountain. Its vestibule permits the rapid insertion of four suc- 

 cessive filters, transmitting different wavelength bands. Such a device 

 should indicate variations in haze more certainly than does the 

 pyranometer without filters as ordinarily used. It is hoped that this 

 filter pyranometer may prove an important aid in determining atmos- 

 pheric transmission values required in short-method solar-constant 

 observations. 



