450 ON THE THEORY OF THREE PRIMARY COLOURS. 



uniformly illuminated with a mixture of the corresponding colours. In order 

 to see these colours separately, another lens was placed between the moveable 

 slits and the screen. A magnified image of the slits was thus thrown on the 

 screen, each slit shewing, by its colour and its breadth, the quality and quantity 

 of the colour which it suffered to pass. Several colours were thus exhibited, 

 first separately, and then in combination. Red and blue, for instance, produced 

 purple ; red and green produced yellow ; blue and yellow produced a pale pink ; 

 red, blue, and green produced white ; and red and a bluish green near the 

 line F produced a colour which appears very different to different eyes. 



The speaker concluded by stating the peculiarities of colour-blind vision, 

 and by shewing that the investigation into the theory of colour is truly a 

 physiological inquiry, and that it requires the observations and testimony of 

 persons of every kind in order to discover and explain the various peculiarities 

 of vision. 



