These were all regarded as Blues 

 of different shades. 



154 Two cases of Insensibiliiy of the Eye 



well described by a distinguished philosopher, and it is princi- 

 pally for the purpose of laying it before our readers that we havd 

 introduced the subject at present. Before doing this, however, 

 we shall describe the case of a young man of about twenty years 

 of age, the son of an eminent scientific gentleman in the vici- 

 nity of Edinburgh, whose peculiarities of vision were examin- 

 ed some years ago by Dr Brewster. 



The following coloured silks he arranged into two sets of 

 colours, viz. blues and browns : — 



Green, 



Pale Blue, 



Purple, 



Carmine Red, 



Pale Pink, 



Peach Blossom, 



Red Lilac Purple, 



French White, 



Dark Green, 



Duck Green, 



Vermillion Red, 



Bright Tile Red, 



Chestnut Brown, J 



The most precise information, however, was obtained from 

 the following experiments : — 



1. The prismatic spectrum was formed with an equilateral 

 prism of flint-glass, which received the light from a very nar- 

 row longitudinal aperture. The colours which were thus de- 

 veloped were four, as in Dr Wollaston''s spectrum, viz. red, 

 green, blue, and violet. When Mr L examined this spec- 

 trum, it appeared to consist only of two colours, — yellow and 

 bliie. 



2. Wlien all the colours were absorbed by a reddish glass 



excepting red and dark green, Mr L saw only one colour, 



viz. yellow. 



3. When the middle of the red space was absorbed, as de- 

 scribed in the Edinburgh Transactimis, vol. ix. p. 439, Mt 



L- saw the black space with what he called the yellow on 



each side of it. 



The case of Mr is very nearly the same with that 



now described ; but there are some peculiarities in it which 

 merit attention. " We have examined,"" says the distinguished 



These are all regarded as Browns 

 of different shades. 



