50S Transactions. — Miscellaneous. 



be recalled after it has given place to another by pressure 

 on the eyeball, either by blinking the eyes, or by touching 

 with the hand. 



The image also seems to wax and wane. This is probably 

 due to the pulsation of blood in the arteries, for I have noticed 

 that by moving my head I could change to some extent the 

 colours of the image. When the eyes are shut and exposed 

 to the light the colours of the image are, as a rule, brighter 

 than when the eyelids are covered. 



By observing the after-image my attention has frequently 

 been called to some detail which I had not noticed in looking 

 at the concrete object. 



I will now give the results of a few experiments I have 

 made for the purpose of noting the change of colour in after- 

 images. 



(1.) I was in a room with the window nearly covered with 

 a dark-green blind, which did not quite reach to the top. The 

 sun was shining brightly through this exposed part. Avoid- 

 ing the glare, I looked for a second at the blue sky, which 

 through the glass appeared almost white, then shut my eyes. 

 Immediately I got a beautiful image — bright blue, with a dark 

 stripe marking the wooden frame dividing the panes (which, 

 by the way, I had not noticed with my eyes open). The blue 

 changed into a bright violet, with a dark stripe, then to a rich 

 yellow, which turned quickly into a deep brown with a light- 

 grey or steel-coloured stripe down the centre. This negative 

 image faded gradually into the surrounding dark back- 

 ground. 



This experiment I repeated several times, with the same 

 general results, but I found that every change in my position, 

 by facing the light or turning my back to it, produced a 

 different sensation. 



So persistent was this after-image that I could open my 

 eyes, look around the room without seeing the image, and 

 shut my eyes again, when the image immediately reap- 

 peared. 



(2.) I looked at the sun shining in the blue sky. The 

 changes in colour were so rapid that I could with difficulty 

 take note of them as they passed. But the general results 

 were as follows : A white spot with a bright purple halo ap- 

 peared in a darker purple background. The halo quickly dis- 

 appeared, and the white spot changed to blue, still with a 

 purple background ; then the purple gave place to yellow, 

 turning to orange, while the spot became yellow with a 

 reddish background. I here pressed my eyeballs, with the 

 result that the blue returned for an instant, but was followed 

 immediately by orange. For a short time a green tint covered 

 both spot and background, and after this had passed the red 



