B. O. Peirce —Sensitiveness of the Eye to Color. 301 
libly detect corresponded to a difference in wave-length of only 
0000005™". This last is rather remarkable, for although no 
one could see any difference between the colors of the edges of 
either of the strips, a displacement which made the color of the 
middle of one strip the same as that of an edge of the other 
Sometimes made the two strips distinguishable. 
There was a singular uniformity in the performance of differ- 
ent eyes as judged by the average of these displacements for 
the whole visible spectrum. Perhaps smaller differences might 
have been detected if the strips had been narrower, but the 
work proved to be so trying to the eyes that I thought it best 
not to experiment further. 
- From a series of observations made by a number of different 
persons and extending over several months, two or three gen- 
eral conclusions may be drawn. ‘To make these evident, I have 
plotted a curve by laying off over different places in the spec- 
trum ordinates obtained by averaging in each case the least 
000005™™. 
aie 
Tn all cases the eye was most sensitive to changes in a color 
Cases the eye was more sensitive to changes in the color corres~ 
ponding to the F line than to changes in colors lying half-way 
between 5 and F one oe 
In many cases, though not in all, the eye was less sensitive 
to changes in’a red near the C line than to a somewhat darker 
red beyond the Lithium line. In the darker colors at theends 
of the spectrum it was, of course, very hard to distinguish small a 
differences, — : 
_ In addition to these general features there were in most of 
the curves obtained by plotting the results of the ae 
_ Observers lesser maxima and minima which showed pecu camiecant 
