66 Conjectures respecting the Principles 



colourless, will appear to be as deeply coloured as the 

 other, but of a different hue. 



The two colours exhibited by the two shadows 

 appear in all cases to harmonize in the most perfect 

 manner, or, in other words, to afford the most pleas- 

 ing contrast to the view. 



These two colours are always such that, if they 

 could be intimately mixed together, the result of that 

 mixture would be perfect whiteness; and, as whiteness 

 results from the mixture of all the different colours in 

 certain proportions, the two shadows may be considered^ 

 as containing all the colours in their just proportions, 

 and the colour of the one shadow may with propriety 

 be said to be the complement of the other. 



Two neighbouring colours are then, and only then, 

 in perfect harmony when the intimate mixture of both 

 would produce perfect whiteness ; and hence it appears 

 that, when two colours harmonize, one of them at least 

 must necessarily be a compound colour. 



In the experiment of the coloured shadows, the 

 colour exhibited by one of the shadows only is real, 

 that of the other is imaginary, being an optical decep- 

 tion, occasioned in some way unknown to us by the 

 colour actually present and by the effects of the differ- 

 ent lights and shades. The imaginary colour, which 

 may be said to be called up in the mind by the other 

 real colour, does not, however, appear to be at all in- 

 ferior to the real colour either in lustre or in the 

 distinctness of its hue. 



Any two harmonizing coloured shadows may be 

 produced indifferently, either with one of the given 

 colours, or with the other of them and white light : 

 pink and green, for instance, are harmonizing colours ; 



