180 
CAPTAIN ABNEY ON THE SENSITIVENESS 
Taking these sets of observations separately, the diagrams show that the fields for 
properly selected luminosities are evidently the same, the D and red lithium being veiy 
close to one another. If we compare the fields for the D and red lithium ra 3 ^s in the 
second table with that of the field for the green (S-iST. 36) in the first table, we shall 
see that they are practically identical, 
Fig. 10. 
The next measurements were made by my assistant, and, since, as before stated, 
his colour fields differ considerably from my own, the confirmation obtained by his 
measurements appears very conclusive. They were made for illustrating a different 
part of the research, hut they will be given here and referred to subsequently. Two 
places in the spectrum were selected, such that the two rays wdien combined wmuld 
give wdrite light, the white being that of the electric light, which is indistinguishable 
from the sensation produced by the coloured rays when falling on the peripheral 
portions of the retina. The first positions selected were in the red and green, at 
X 6500 and X 5002, corresponding to the scale of the spectrum with the numbers 
57'8 and 34. Tlie relative luminosities of the rays reaching the eye were 225 and 270 
respectively. 
