40 Messrs. Paterson and Dudding on Estimation of 



the optical scale, using- pyrometers for which the dominant 

 wave-length is \ — 0'650/jl. 



Fig. 2 shows the curve connecting current in the lamps 

 and the temperature of" the black body for colour identity in 

 the case of each of these lamps. It was found that the 

 sensitivity of the process of colour matching is more 

 than equal to that of temperature measurement by optical 

 pyrometers. 



Fig. 2. — Carbon (A) and Tungsten (B) Colour Standards. 



"S3 



51 



2400 

 2200 

 2000 

 1800 

 1600 

 1400 

 1200 

 1000 



1 





l i 





I I I 



1 1 









R 















® Observations made on Dec. 3, 1S12 







V 



/ 



















. C 



bsc 



inn 



stio 



13 









Ja 



i. 1 



. 1913 







< 











































/ 

















A 































p 

















X 



k* 



























/ 









































/ 













^ 



f\ 



























1/ 













^ 



^ 































/ 









^ 



A 

































f 











/ 



r 











\ 























/ 



' I 





/ 



y 















1 























/ 









/ 

























































































































































































































0-1 



02 03 



0-4 05 0-6 07 

 Current in Amperes. 



1-2 



Curves connecting the current in the lamps with the temperature of 

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

 the lamps. 



Duplicates of these two lamps were then made for use in 

 experiments where their continued employment at the higher 

 efficiencies might affect their constancy. 



2. " Colour Identity" Temperatures Corresponding 

 with Different Efficiencies. 



It is common for the specific consumption of glow-lamps to 

 be stated in terms of the watts per mean horizontal candle. 

 The only rigorous way, however, is to state it in terms of 

 watts per mean spherical candle or in lumens per watt. 

 Throughout this paper the latter designation is used, repre- 

 senting as it does the true measure of the ratio of the total 

 light emitted to the power supplied. In the table of results 



