176 .\]SnsTUAL REPORT BMITHSONIAINT INSTITUTION, 1940 



Using the same device operated at the freezing points of rhodium 

 and iridium in addition to platinum, Wensel, Judd, and Koeser (10) 

 established an accurately reproducible scale of color temperature. 

 This scale is made available to the public through the distribution 

 of color-temperature standards in the form of tungsten-filament 

 lamps. 



Comparison of the blackbody standard with the present inter- 

 national candle as maintained by groups of carbon-filament lamps 

 showed that the brightness of the new standard was about 58.9 inter- 

 national candles per square centimeter. However, a uniform pro- 

 cedure has not been followed internationally in the step-up from the 

 yellower sources to the modern tungsten lamps, and E. C. Crittenden 

 found that a better agreement with present practice would be reached 

 by defining the brightness of the standard blackbody radiator as equal 

 to 60 candles per square centimeter. Other national laboratories have 

 agreed to the Bureau's suggestion to adopt this value, and this recom- 

 mendation has been approved by the International Committe of 

 Weights and Measures. In stepping up from the blackbody standard 

 to tungsten lamps, it is proposed to use the luminosity factors recom- 

 mended by Gibson and Tyndall (11) of the Bureau staff in 1923, and 

 later adopted by both the International Commission on Illumination 

 and the International Committee of Weights and Measures. At last 

 we have an international primary standard of brightness. 



BIBLIOGRAPHY 



(1) Thomas, J. L. 



1930. Nat. Bur. Stand. Journ. Res., vol. 5, p. 295. 



(2) CUKTis, MooJT, and Sparks. 



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(3) CxjETis, H. L., and Cubtis, R. W. 



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(4) Heyl, p. R., and Cook, G. S. 



1936. Nat. Bur. Stand. Journ. Res., vol. 17, p. 805. 



(5) Burgess, G. K. 



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(6) HoGE, H. J., and Beickwe35De, F. G. 



1939. Nat. Bur. Stand. Journ. Res., vol. 22, p. 351. 



(7) Taylor, L. S., and Singer, G. 



1930. Nat. Bur. Stand. .Tourn. Res., vol. 5, p. 507. 



(8) CoBLENTz, W. W., and Stair, R. 



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(11) Gibson, K. S., and Tyndall, E. P. T. 



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