HOMOGENEOUS YELLOW LIGHT. 107 



duced upon coloured objects by illuminating them 

 with homogeneous light, or light of one colour. 

 The light which emanates from the sun, and by 

 which all the objects of the material world are 

 exhibited to us, is composed of three different 

 colours, red, yellow, and blue, by the mixture of 

 which in different proportions all the various 

 hues of nature may be produced. These three 

 colours, when mixed in the proportion in which 

 they occur in the sun's rays, compose a purely 

 white light ; but if any body on which this white 

 light falls shall absorb, or stop, or detain within 

 its substance any part of any one or more of 

 these simple colours, it will appear to the eye of 

 that colour which arises from the mixture of all 

 the rays which it does not absorb, or of that 

 colour which white light would have if deprived 

 of the colours which are absorbed. Scarlet cloth, 

 for example, absorbs most of the blue rays and 

 many of the yellow, and hence appears red. 

 Yellow cloth absorbs most of the blue and many 

 of the red rays, and therefore appears yellow ; 

 and blue cloth absorbs most of the yellow and 

 red rays. If we were to illuminate the scarlet 

 cloth with pure and unmixed yellow light, it 

 would appear yellow, because the scarlet cloth 

 does not absorb all the yellow rays, but reflects 

 some of them ; and if we illuminate blue cloth 

 with yellow light, it will appear nearly black, 

 because it absorbs all the yellow light, and 

 reflects almost none of it. But whatever be the 

 nature and colour of the bodies on which the 

 yellow light falls, the light which it reflects must 

 be yellow, for no other light falls upon them, and 

 those which are not capable of reflecting yellow 



