High Temperatures by the Method of Colour Identity. 45 



filaments squirted or drawn, appears to leave unaffected 

 the relation between lumens per watt and the corresponding 

 *' colour identity " temperature of a black body for either of 

 these types. 



Fisr. 4. 



2-2 



2-0 



11-6 



o 



42 1*4 



I 



Sl'2 



ro 



08 



C6 



3 20 















i 















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r L 



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, s- 



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s 



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tf 



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Cr 



























rr 



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r 





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xt 























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Y 



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S* 



>> 



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333 340 



322 324 326 328 330 3 32 3 34 336 

 Log of Temperature of Black Body at Colour Match. 



Curves connecting watts consumed by carbon and tungsten filament 

 lamps, and the temperature of the black body whose radiation 

 matches in colour that of the lamps. 



A is for Lamp No. 5. (Carbon filament.) 



B „ „ No. 3. ( „ ., ) 



C ,, „ No. 12. (Tungsten ,, ) 



D „ „ Nos. and 8. ( „ „ ) 



It will, therefore, be seen that all the results may be taken 

 as lying on two curves, one representing the carbon group 

 and the other the tungsten group, and so closelv do the 

 points keep to the curves that very few observations lie more 

 than 1 per cent, in temperature from the mean curve. 



This implies that in all ordinary lamps of the same cha- 

 racter (vacuum tungsten or carbon) the colour of the radiation 

 from the whole filament, including the cooled ends, is the 

 same for the same value of lumens per watt. Therefore, to 

 considerable accuracy, it may be said that a knowledge of 

 the lumens per watt of a lamp implies a knowledge of the 

 temperature of a black body whose radiation is the same in 

 hue as that of the lamp. 



