MAR. 4, 1923 CRITTENDEN: MEASUREMENT OF LIGHT 75 
same as for another, and the continual necessity for specifying what 
kind of candlepower one means is a strong argument for using the 
unambiguous “lumen.’’ Incidentally the appropriate use of the flux 
rating which tells how much light is produced serves to make more 
clear the real significance of candlepower as indicating the distri- 
bution of the flux about the source. 
STANDARDS OF CANDLEPOWER 
Primary Standards.—While all countries agree in making their 
measurements start from concrete standards of candlepower, and 
general agreement, with the exception of the Germanic nations, has 
been reached on a common unit of candlepower, there has been wide 
divergence in regard to the standards which shall be considered as 
fundamental. In all countries the name given to the unit is candle, 
or an equivalent word, but no country has actually retained the 
candle as a standard. In passing from it, however, each country has 
followed an independent course, and consequently the nominal basis 
of the unit is different in each of the four great nations, France, Great 
Britain, Germany and the United States. The first three of these 
adopted different flame lamps as primary standards. If the units 
were actually redetermined from these standards it is probable that 
differences would appear among the units thus derived. 
In France the classic basis for the value of the candle is the Violle 
platinum standard (the normal intensity of one square centimeter of 
platinum at the melting point), but no one ever succeeded in repro- 
ducing Violle’s results, and it is now recognized that this standard is 
far from being exactly reproducible, because the radiation from 
platinum is so susceptible to the influence of surface conditions and 
surroundings. In practice Violle’s determination of the unit was 
applied by using the Carcel lamp with the value which he assigned 
to it. and until recently this lamp has been retained as a reference 
standard. A law passed in 1919, however, while still referring to 
the Violle standard, specifically says that the unit, the Bougie 
Décimale, is represented practically and in a permanent manner by 
means of incandescent electric lamps deposited in the Conservatoire 
Nationale des Arts et Métiers. In Great Britain the candle was 
superseded by the Harcourt 10-candle pentane lamp, but it is difficult 
to reproduce such lamps exactly, and the accepted standard is not 
the pentane lamp in general, but a particular lamp of this kind at 
the National Physical Laboratory. Moreover, the standards actually 
used at the National Physical Laboratory are electric incandescent 
