334 



Tables 349-351 



TABLE 349. — Photometric Standards 



In Germany the Hefner lamp is most used; in England the Pentane lamp and sperm 

 candles ; in France the Carcel lamp is preferred ; in America the Pentane and Hefner 

 lamps are used to some extent, but candles are largely employed in gas photometry. For 

 the photometry of electric lamps, and in accurate photometric work, electric lamps, stand- 

 ardized at a national standardizing institution, are employed. 



The " International candle " designates the value of the candle as maintained by co- 

 operative effort between the national laboratories of England, France, and America; and 

 the value of various photometric units in terms of this is given in the following table 

 (Circular No. 15 of the Bureau of Standards). 



I International Candle = 1 Pentane Candle. 



1 International Candle = 1 Bougie Decimale. 



1 International Candle = 1 American Candle. 



1 International Candle =1.11 Hefner Unit. 



1 International Candle = 0.104 Carcel Unit. 



1. Standard Pentane Lamp, burning pentane 10.0 candles. 



2. Standard Hefner Lamp, burning amyl acetate 0.9 candles. 



3. Standard Carcel Lamp, burning colza oil 9.6 candles. 



4. Standard English Sperm Candle, approximately 1.0 candles. 



TABLE 350. — The Waidner-Burgess Standard of Light 



The Waidner-Burgess standard light consists in immersing a hollow inclosure in a bath 

 of molten platinum and observing the light from the inclosure during the period of freez- 

 ing. The exceptionally pure Pt was in a thorium oxide crucible heated by an induction 

 furnace. At all times before and after test the Pt was 99-997% pure. Reproducible to 

 0.1% the brightness is 



58.84 International Candles per cm 2 



(Wensel, Roeser, Barbrow, Caldwell, Bur. Standards Journ. Res., 6, 1103, 1931.) 



TABLE 351. — Intrinsic Brightness of Various Light Sources 



Taken from Data, 191 1. 



Smithsonian Tables 



