p. LECOMTE DU NOUY 



761 



g 



240 

 220 

 200 

 180 

 160 



J 140 

 V 



& 120 

 +-» 



I 100 



f 



^ 80 

 O 



60 



40 



20 



— I \ 1 1 1 1 1 1 1 1 !??? 1 r"*T*""MlMM <^ 



X 0.5 1 1.5 2 



8 



/^ 



Fig. 6. Energy distribution curve of the Nernst lamp used (uncorrected), 91.8 

 watts: slits: 0.025 mm. 



Criticisms of the Results. — As has been pointed out before by 

 Langley, the errors involved in the determination of the threshold 

 of sensitivity (minimum visihile) may be perhaps 100 per cent, or 

 even more. For this reason, the absorption by the various eye 



