Unit of Candle-power in White Light. 71 



Jamps, therefore, required careful preliminary testing, and 

 many had to be discarded in the process. In the early days 

 of the tungsten lamp several complete sets of standards had 

 to be discarded after their seasoning was finished and stan- 

 dardization work had begun, owing to the appearance of small 

 changes of candle-power. 



The details of the various sets of lamps are 

 Table I. 



Table I. 





Approx. 





Temp, of 







Set. 



watts. 



per 



M.H.C. 



No. of 



lamps. 



black body 



for colour 



match. 



Approx. 

 c.p. 



Description. 



1 



7-7 

 (Carbon 

 basis) 



11 



1610° C. 



15 



Six tungsten hairpin filaments sus- 

 pended in grid form in one plane. 

 Height of filaments 120 mm. 

 Volts 105. Matches the colour of 

 the 10-candle pentane lamp. 



2 



4-8 

 Carbon 

 basis) 



11 



1700° C. 



15 



Single carbon loop filament in one 

 plane. Height of filament 110 mm . 

 Volts 100. 



3 



3-9 



10 



1750° C. 



32 



Five tungsten hairpin filaments sus- 



(Carbon 









pended in grid form in one plane. 



basis) 









Height of filaments 120 mm. 

 Volts 109. 



4 



33 



(Carbon 

 basis) 

 19 



10 



1790° C. 



15 



Gem coiled metallized carbon filaments 

 (usual pattern). Volts HJO. 



5 



13 



1870° C. 



12 



Four tungsten hairpin filaments sus- 





(Tungsten 









pended in grid form in one plane. 





basis) 









Height of filaments 70 mm. 

 Volts 95. 



(> 1-5 



10 



1950° C. 



18 



Four tungsten hairpin filaments sus- 



(Tungsten 









pended in grid form in one plane. 



basis) 









Height of filaments 70 mm. 













Volts 105. 



Absolute Value of the Unit of Candle-power. 



The foregoing description deals with the method used to 

 determine the ratio of the average value of one set of sub- 

 standards in terms of another, and therefore deals only 

 with relative values. The absolute values of candle-power 

 of sets 1 and 2 have been assigned to them respectively by 

 two independent comparisons with the Harcourt 10-candle 

 standard lamp. Set No. 2 (consisting of Fleming-Ediswan 

 lamps) was compared against the pentane lamp in 1004-6. 

 It will be seen from Table T. that the light from set 2 was 



