SENSATIONS IN TKKMS < >F U'.MINOSITY. 



- - 7 



In fig. 10 it will be noticed that A and D of fig. 1 are somewhat closer together, 

 and that the place where the blue sensation exists mixed with white alone, is again 

 close to the blue lithium line. The blue sensation curve is also somewhat higher. 



Confirmatory of these curves are the luminosity curves given for the red blind in 

 ' Colour Photometry,' Part III. If the curves there given be reduced to a little more 

 than one-half the scale of nnlinates, they will be found to closely correspond to those 

 of fig. 4. It must be remembered that to them the red luminosity is non-existent 

 throughout the spectrum, hence the luminosity of the violet end is much diminished. 

 For this reason the luminosity curves were made on too high a scale when drawn for 

 that paper, and they should be corrected accordingly. It need not follow from this 

 investigation that the colour-blind see less light than those having the three full 

 sensations, though the "extinction" readings given in that same paper seem to indicate 

 that such is the case. A further investigation into this is in hand, and for the 

 present the question must be left an open one. 



I have to thank my assistant, Mr. WALTER BRADFIELD, for the aid he has given 

 me in this investigation. The actual observations recorded were made by myself, but 

 all preparatory work was done by him. 



