190 
CAPTAIN ABNEY ON THE SENSITIVENESS 
Table XXL 
Annulus 
Compara¬ 
tive 
Red lithium. 
D. 
41-7 S.N. 
Blue 
lithium. 
reading. 
intensity 
of light. 
Nasal. 
Temporal. 
Nasah 
Temporal. 
Nasal. 
Temporal. 
Nasal. 
Temporal. 
0 
I 
42 
54 
47 
60 
33 
43 
42 
53 
; 35 
1 
O 
37 
46 
42 
53 
29 
35 
37 
46 
70 
1 
4 
32 
38 
36 
45 
24 
28 
31 
37 
105 
s 
26 
31 
31 
38 
20 
21 
26 
30 
110 
1 
1 6 
22 
24 
26 
29 
15 
8 
21 
24 
! 
All we have to deal with here are the readings on the temporal side. We find 
that for each diminution of one-half intensity the field contracts 7° f)', or twice that 
of the writer’s. The figures in the table on the previous page are now explained, and 
they compare fairly with the results tabulated on p. 186. The variation in sensitive¬ 
ness in different eyes is here well illustrated. 
18. Dependence oj Field on the Size of the Coloured Spot. 
It has been shown that the loss of colour in the centre of the retina depends 
largely on the size of the spot of light viewed. Such being the case, it was to be 
presumed that the boundaries of a field would contract if the aperture used in the 
apparatus was diminished, and it seemed possible that some expression might be 
found which would connect the two together. 
To make measurements of field with dimishing apertures the same kind of 
perimeter was employed as before, and the spot of light on the ground glass was 
diminished in size by placing circular apertures of diminishing diameter in contact 
with it. The fields were measured in a horizontal direction only at first, and the 
following table gives the mean of the actual measures. The intensity of the D light 
was IT AL. 
