Vision of Colours of Varying Intensity. 83 



. Table I. 



Persistence of Vision and Luminosity. 

 0°. 20°. 40°. 60°. 





















X 



D 



L 



D 



L 



D 



L 



D L 



725 fi 



•0286 sec. 



11-7 



•0290 sec. 



11-3 



•0312 sec. 



9-5 



•0366 sec. 6-8 



665 



•0184 



461 



•0187 



433 



•0198 



351 



•0224 23-2 



590 



•0153 



100-0 



•0155 



94-5 



•0162 



77-0 



•0178 52-7 



520 



•0169 



646 



•0172 



60-3 



•0182 



48-0 



•0202 32-8 



460 



0254 



160 



•0261 



14-9 



•0279 



12-4 



•0317 9-2 



430 



•0448 



4-9 



•0461 



4-7 



•0507 



4-0 



0622 31 





70° 



L^ 



80° 

 D 



IP 



85° 





87° 18'. 



X 



B 



L 



r~ "^ ~^ 

 D L 



•725 p 



•0436 sec. 



51 



•0603 sec. 



33 









665 



•0251 



16-6 



•0321 



8-7 



•0454 sec. 



4-8 



•0625 sec. 3-0 



590 



•0196 



36-5 



•0238 



19-2 



•0303 



10-3 



•0366 6-8 



•520 



•0224 



23-2 



•0268 



139 



•0340 



7-9 



0415 5-5 



•460 



•0359 



7-2 



•0476 



4-4 



•0694 



2-8 



•0795 2-45 



•430 



•0805 



2-5 



•0980 



21 



•0936 



• 2'2 





•585 



•0194 



37-9 













•583 







•0232 



20 V 7 









•575 











■0300 



10-4 





572 















•0360 71 





88° 12 



r 



88° 30'. 



. A 









X 



D 



jET 





L 









•725 [i 

















•665 



•0820 sec. 



2-4 













•590 



•0397 



5-9 



•0434 sec. 



51 









•520 



•0467 



4-6 













•570 



•0391 



6-1 













In the columns under D are the values of the persistence 

 of vision, or the duration of the visual impressions. In the 

 columns under L are the luminosities corresponding to the 

 values of D. These are obtained by assuming a luminosity 

 of 100 for the smallest value of D, 0*0153 sec, in the whole 

 table, and then applying the Ferry-Porter law in its simple 

 form 



d =ttV 



k log Li 



for the other values of D in all the columns. 



In fig. 2 the values of D and the wave-lengths are used as 

 coordinates, which give a series of nine persistency curves for 

 intensities varying almost to invisibility. The curve for the 

 brightest spectrum corresponding to the angle 0° between 

 the sections of the nicols is at the bottom of the figure, and 

 that for the dimmest spectrum at the top. In the "curve" 

 lor 88° 30' only one point was obtained. It will be noticed 



G2 



