58 



Prof. F. Allen on Four Transition Points in tit 



was fatigued with a pure red, 



curve obtained when the eye 



of wave-length X'680/z 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 Avas the wave-length X '589 /x, 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 fi, and the readings in Table I. 

 were obtained. 



Table I 



"733 fx 



•695 



•663 



•601 



•564 



Normal 



Persistence. 

 •0340 sec. 

 •0248 

 •0198 

 •0156 

 •0157 



Eye fatigued 

 with X -670 p. 



•0880 see. 



■0266 



•0214 



•0155 



•0155 



•530 ,x 



•500 



•470 



•460 



•430 



Normal Eye fatigued 

 Persistence, with X *670 /*. 

 •0171 sec. '0175 sec. 

 •0215 -0224 



•0306 

 •0332 

 •0513 



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

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

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

 and X "625 fi, the data for which are tabulated in Table II. and 

 Table III. respectively. 







Table II. 







X. 



Normal 

 Persistence. 



Eye fatigued 

 with X '651 /x. 



X. 



Normal 

 Persistence. 



Eye fatigued 

 with X *651 ft. 



•733 fi 



•695 



•663 



•601 



•564 



•0318 sec. 



•0232 



•0185 



•0144 



•0147 



•0353 sec. 



•0254 



•0197 



•0145 



•0153 



Tabl 



•530 ii 

 •500 

 •460 

 •430 



Bin. 



•6i89 sec. 

 •0310 



•0458 



•0177 sec. 

 •0189 



X. 



Normal 

 Persistence. 



Eye fatigued 

 with X'625/i. 



X. 



Normal 

 Persistence. 



Eye fatigued 

 with X - 625 ix 



•733 /x 



•695 



•663 



•601 



•564 



•0318 sec. 



•0232 



•0185 



•0144 



•0147 



•0364 sec. 



•0249 



•0190 



•0144 



•0162 



•530 it 

 •500 

 •460 

 •430 



•0189 sec. 



•0310 



•0458 



•0170 sec. 

 •0194 



