284 



On Negative After-images, &c. 



any other colour, and if the appearance of purple in the pulsative image 

 may be regarded as a test for the presence of green in the luminous 

 object, then it appears from Nos. 4, 8, and 9 that green is a constituent 

 of yellow, of blue, and of white. 



Table II. 



Kef. 

 No. 



12 



Spectrum 

 colours. 



Complementary 

 colours. 



Extreme red 



Green-yellow 

 Green 



Blue-green 

 Blue 



Blue-violet 

 and violet 



Purple 



White 



Spectrum. . 



G-reen-blue . . 



Red i Blue-green. . . . 



Orange Blue 



Yellow | Blue-violet . . 



Violet 



Purple 



Eed 



Orange-yellow 



Yellow 



Green 



Neutral grey. . 



Pulsatire 

 colours. 



Remarks on pulsative 

 image. 



Green-blue 



Blue-green 



Pale blue-green 



Nearly neutral 



Pink, or 

 purple 



Purple 



Purple 



(1.) Dull pink 

 (2.) Orange 



(1.) Bluish-pink 

 (2.) YeUow 



Blue-green .... 



(1.) Purple or 

 purplish -grey 

 (2.) Neutral 



The image could only be 

 seen by direct vision. 

 None was formed on the 

 screen. 



The most intense of all 



pulsative colours. 

 Green-blue with strongest 



illumination and direct 



vision. 



Pinkish with ordinary il- 

 lumination, bluish with 

 strong. Always incon- 

 spicuous. 



Mixed red and green light 

 gave images similar to 

 those of Nos. 4 and 5. 



Inferior only to No. 1 in 

 intensity. Easier to pro- 

 duce than any other. 



Nearly the same as No. 6. 



(1.) For ordinary illumi- 

 nation and on screen. 

 (2.) Eor intense illumi- 

 nation with direct vision. 



Remark as for No. 8. 

 Yiolet gave no visible 

 image upon screen. 



Same as No. 2. The addi- 

 tion of blue to red made 

 no perceptible differ- 

 ence. 



(1.) With all ordinary 

 illumination, for reconi- 

 bined spectrum and for 

 combinations of red and 

 green and of yellow and 

 blue. (2.) With strong 

 direct sunlight. 



Blue-green and purple 

 very conspicuous ; all 

 other colours compara- 

 tively feeble. 



The weakness of the pulsative image of yellow is remarkable, and 

 cannot be readily explained. If a yellow colour-patch is formed by 

 combining red and green rays, and the image is then put slightly out 



