and Coloured Shadows. .431 



have given an experiment more completely in accordance 

 with my theory ; the diminished sensibility of the eye to 

 green light, renders the white ground pink (violet and red 

 diluted with white); the blue ground (violet and green) 

 violet ; and the yellow ground (red and green) orange, the 

 eye not being wholly insensible to green light, which would 

 be necessary to produce an accidental colour of pure red. 

 But if blue and yellow are simple colours, from what 

 source is the violet produced on the blue ground ; or the 

 red, to form the orange on the yellow ground ? 



The accidental colour is always the complement of the 

 colour to which the eye has been previously exposed, with 

 reference to the ground upon which it is seen ; or, more 

 definitely, the colour of the ground, minus the colour with 

 which the eye is impressed, in the degree to which it has 

 been rendered insensible to this colour. 



If we look at a sheet of white paper through a piece of 

 green glass, in the manner Mr. Tomlinson has directed, (1) 

 the paper appears upon the first impression to have a 

 decidedly green tint ; but if we continue our view, this tint 

 quickly declines in intensity, until, at length, it becomes 

 gray with only a slight tinge of the colour of the glass. — 

 If we suddenly remove the glass from the eye in the 

 different stages of this experiment, we shall find that the 

 intensity of the accidental colour will be inversely in pro- 

 portion to the intensity of the primitive colour; if, for 

 instance, we remove the glass after the first impression, 

 the paper will appear white ; the following moment it will 

 have a slight tint of pink, and this tint will increase, as 

 the eye becomes more impressed, precisely in proportion 

 to the decline of the primitive colour, until, under favour- 

 able circumstances, it becomes crimson. 



Here, then, we have a direct proof, that the sensation 

 produced by light declines immediately after the first im- 

 impression ; but we have no reason to apprehend the evils 

 which Mr. Tomlinson supposes must result from it ; (7) 

 for the transition from one state to the other is made with 

 such rapidity, that the motion of the eye from one colour 

 to a difierent, adjoining colour, gives sufficient time for the 

 recovery of its functions ; and even the short intermission 

 caused by the motion of the eye lids, which is probably 



