58 



Prof. ¥. Allen on Four Transition Points in the 



curve obtained when the eye was fatigued with a pure red 

 of wave-length \'680/x has in it a single characteristic 

 elevation which corresponds to the red portion of the 

 spectrum, the rest of the curve coinciding with the normal.. 

 It will also be noticed from fig. 8, that when the fatiguing 

 colour was the wave-length \ \589 //,, there were two elevations 

 in the curve, one in the red as before, and the second in the 

 part corresponding to green. It occurred to me that there 

 must be in the spectrum a point of transition from the type 

 of curve with one elevation to that with two, and that the 

 curve obtained when this transition point was made the 

 fatiguing colour would probably differ in some way from 

 both. Accordingly, search was made for it. The eye was 

 fatigued with the colour X '670 /x, and the readings in Table I.. 

 were obtained. 



Table I. 



x. 



•733 [x 



•695 



•663 



•601 



•564 



Normal 

 Persistence. 

 •0340 sec. 

 •0248 

 •0198 

 •0156 

 •0157 



Eye fatigued 

 with X -670 /i. 



•0380 see. 



•0266 



•0214 



•0155 



•0155 



X. 



•530 fi 



•500 



•470 



•460 



•430 



Normal Eye fatigued 

 Persistence, with X - 670 fi. 



•0171 sec. 

 •0215 



•0332 

 •0513 



•0175 sec. 



■0224 



•0306 



These values are plotted in fig. 3, and give a curve with 

 one elevation, similar to that for the wave-length X '680 /*.. 

 Similarly, curves were obtained for the wave-lengths A '651 /u 

 and A, *625 yu,, the data for which are tabulated in Table II. and 

 Table III. respectively. 



•733 fx 



•695 



•663 



•601 



•564 



Table II. 



Normal 

 Persistence. 

 •0318 sec. 

 •0232 

 •0185 

 •0144 

 •0147 



Eye fatigued 

 with X '651 fx. 

 •0353 sec. 

 •0254 

 •0197 

 •0145 

 •0153 



X. 



•530 ^t 



•500 

 •460 

 •430 



Normal Eye fatigued 

 Persistence, with X '651 /x. 



•0177 sec. 

 •0189 sec. -0189 

 •0310 



•0458 



Table III. 



A. 



•733 /x 



•695 



•663 



•601 



•564 



Normal 

 Persistence. 

 •0318 sec. 

 •0232 

 •0185 

 0144 

 ■0147 



Eye fatigued 

 with X'625/x. 



•0364 sec. 



•0249 



•0190 



•0144 



•0162 



X. 



•530 A t 

 •500 

 •460 

 •430 



Normal 

 Persistence. 



•0189 sec. 



•0310 



•0458 



Eye fatigued 

 with X *625 fx. 



•0170 sec. 



•0194 



