44 Messrs. Paterson and Dudding on Estimation of 



the range between the highest and the lowest observed 

 values. 



Fig. 3.— Ordinary 100 and 200 volt Carbon (Curve A) and Tungsten 

 (Curve B) Filament Vacuum Lamps. 







































































_, 



































































,- 



-- 





„- 



























































, 



,-• 



'' 



,, 



-- 



* 

















































































^2400 









































A 







































































.*-* 



8 





























•g 































































































































































































































































































,£2100 

















= 



<• 

































































^ 























































- 





o 













/ 























































15 











b 

























i 





































2 1900 









r 









i 











































n 













/ 



/• 



























I 



































J 1800 







7 









i 













































1 











n 



/ 































; 























i 











Q 































i 



| 























r- i 









*} 



J 

































j 















1 







r 1 j 







© 



I 

































I 



! 





















| i 











1 



































I 





















1 









is „ 

















































I 











£ 















































































































































































1 





















i 











1300 



































1 



1 





















1 











1 2 3 4 5 6 7 8 9 10 1! 12 13 14 15 1ft 17 



Lumens per Watt 



durves connecting lumens per watt of the lamps with the temperature 

 of a black body whose radiation is identical in colour with that of 

 the lamps. 



P This is illustrated in fig. 4, in which the logs of temperature 

 and watts have been plotted for both carbon and tungsten 

 lamps Nos. 3, 5, 6, 8, and 12. It is safe from a knowledge 

 of the watts in any lamp to deduce intermediate temperature 

 values from such a curve, so that the actual number of colour 

 comparisons may be a minimum , and the burning period of 

 the colour standard reduced. 



The watt-temperature relation is given, for carbon filament 

 lamps, by 



W oc T 4 ' 58 , 



and for tungsten filament lamps by 



W og T 5 ' 1 . 



Considering again fig. 3, the first point to notice is that no 

 difference can be detected between the various carbon lamps 

 tested or between the different tungsten lamps. Whether 

 the carbon filaments are flashed or unflashed, and the tungsten 



