40 



Dr. E. S. Clay. On the Application of 



Thus, if the pink ink is only partly transparent in the blue and has 

 not an abrupt absorption there it will not much matter, provided it is 

 perfectly transparent in the red and orange, and has an absorption 

 commencing suddenly in the yellow. Such an ink is Fleming's 

 "Theoretical Eed," No. 1303. 



The yellow must be perfectly transparent in the red, orange, yellow, 

 and green with an absorption commencing in the blue ; but it does 

 not matter if it is not very sudden. 



The blue ink must be perfectly transparent in the green, blue-green, 

 and blue ; there must be an abrupt absorption in the yellow. The 

 violet does not matter so much. So far I have found no ink to fulfil 

 these conditions. All the ordinary inks are too opaque in the green 

 and blue-green. 



9. The Luminosity as well as the Hue of the Spectrum must be Matched 



everywhere. 



It must not be forgotten that most natural colours are composed 

 of a large range of spectrum colour, and the resultant hue will 

 depend on the proportion in which these colours are compounded. 

 Now although the eye is a bad judge of the luminosity of the colour, 

 it is a very good judge of the resultant hue of a compound colour 

 (and thus indirectly it is of course able to compare the relative 

 luminosity of its components as far as this luminosity is due to 

 colour as distinct from white). It follows that the component colours 

 must be rendered in their correct proportions. When a negative is 

 exposed through its light-filter the light that will reach it from a 

 natural object will be the sum of all the colours that the object reflects, 

 each rendered according to the curve of the filter. Suppose for instance 

 that all the light from the orange to the green is reflected by the 

 object as in the first figure. 



Or 



Then if the second figure represents the curve of the light-filter, the 

 area of the shaded portion gives the amount of transmitted light 



