COMMON THINGS COLOUR. 



The means by which these three primary colours produce the 

 tints of the spectrum may be more clearly understood by reference 



Fig. 16. 



to fig. 16, wherein M N represents the prismatic spectrum with its 

 usual tints. The curve M R x represents the varying intensity of 

 the red spectrum, M Y N that of the yellow, and M B N that of 

 the blue spectrum. The distance of each part of these curves 

 respectively from M N is understood to be proportional to 

 the intensity of the colour of that part, and the relative 

 lengths of the perpendicular included within each curve repre- 

 sents the proportion of the intensities of the combined colours. 

 Thus, at the point p, the three colours are mixed in the proportion 

 of the lengths of the perpendiculars p n, p' n, p" n, the first 

 representing the proportion of yellow, the second red, and the 

 third blue ; the red and yellow predominating, the colour at this 

 point will be orange. 



These observations and experiments, and the conclusions 

 deduced from them by Sir David Brewster, have been now before 

 the scientific world for more than twenty years. The experiments 

 do not appear to have been repeated, nor the chromatic doctrine 

 inferred from them to have been yet generally assented to or 

 adopted. The chromatic analysis of Newton is the only theory 

 advanced by physical authors. 



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