Negative After-Images and Successive Contrast. 435 



orange, yellow, or green. There was strong action on the blue and violet, 

 these became much darker and bluer along the line of the after-image. 



2. The fatiguing light was A 654-A 675 as before, but a filter was inter- 

 posed in the path of the rays forming the screen spectrum so that only red 

 and orange appeared upon the screen. After the fatigue the red disappeared 

 but the orange remained. This was tried with a screen spectrum fairly 

 strong and also very weak, with the same result. 



3. After exposure to A 654-A 675 (orange-red) a sodium flame was viewed 

 and found to be very little affected in the region of the after-image (no effect, 

 AW. P.) (slightly greener, E.-Gr.), though the green-blue after-image was 

 very strongly marked on either side of the sodium flame. 



4. The fatiguing range was A 619-A 631 (orange). The dark blue after- 

 image was seen right across the spectrum except in the region of the orange, 

 which appeared unaffected. 



5. The fatiguing range of A 619-A, 631 was also used with a screen 

 spectrum showing only orange and red. The same result was obtained as 

 with the red, namely, the red disappeared, being replaced by the green-blue 

 after-image, whilst the orange appeared unaffected. 



6. Fatiguing range, A585-A595 (orange-yellow). Purple after-image seen 

 right across spectrum. The red was affected most. The general impression 

 was that the band appeared as if painted over the spectrum. 



7. Fatiguing range, A 545-A 550 (yellow-green). Purple after-image similar 

 to above and effects similar to A 585-A 595, least effect in orange. 



8. Fatiguing light, A 496-A 500 (blue-green). Exactly the same effect as 

 before, with A, 545-A 550. Orange least affected ; purple not red after- 

 image. When an after-image was projected on a sodium flame, no effect 

 (A. W. P.), (slightly redder, E.-G.). 



9. Fatiguing light, A 475-A480 (blue). After-image reddish-purple, no 

 action on red and orange, the after-image seen over the rest of the spectrum. 



10. Fatiguing light, A 445-A455 (blue). After-image yellow-green (AW. P.) 

 or orange (E.-G-.) ; violet and blue cut off, green and red made yellower. 

 When a filter was used so that only green and red were seen on the screen, 

 the green was cut out by the after-image, but the red was unaffected. 



11. Fatiguing light, A425-A436 (violet). The after-image was green, which 

 made the violet and blue appear green, and made the green appear slightly 

 a yellower green, and did little or nothing to red or orange. 



12. Another method was now adopted, so that a definite and sudden 

 reduction of luminosity in the spectrum on the screen could be obtained 

 when required. This was accomplished by the interposition of Mcol prisms 

 in the path of the light forming the spectrum on the screen. The eyes 



