1892.] on the Sensitiveness of the Eye to Light and Colour. 607 



of the retina, and as it is on this central part that we receive any small 

 image, it has a very important bearing on all colour experiments. 

 The yellow spot absorbs the blue-green, blue, and violet rays, and 

 exercises its strongest absorption towards the centre, though pro- 

 bably absent in the very centre, that is, in the "fovea centralis," and 

 is less at the outer edges. That absorption of colour by the yellow 

 spot takes place can be shown you in this way. Any colour in 

 nature can be imitated by mixing a red, a green, and violet together, 

 and with these I will make a match with white and then w^ith brown, 

 two very representative colours, if we may call them colours. Now 

 if I, standing at this lecture table, match a white by mixing these 



FiCx. 4. 



Colour Sensations. 



three colours together, using a large patch, the image will fall on a 

 part of the retina of considerably larger area than the yellow spot, and 

 it will appear too green for those at a distance ; but it is correct for 

 myself. If I place a mirror at a distance, and make a match again 

 by the reflected image, the match is complete for us all, as vre all 

 see it through the yellow absorbing medium. If I look at it direct 

 from where I stand the match is much too pink. It may be asked 

 why the comparison patches and the mixed colours do not always match 

 since both images are received on the same part of the retina. The 



