110 



HABIT AND INTELLIGENCE. 



[CHAF. 



is necessary, in order to give any riglit conception of the laws 

 of the composition of colours, 

 and tlie It is possible to arrange the colours of the spectrum in such 



oiiposite ^ circular order, that every opposite pair of colours in it shall 

 colours are ' •j i x , . , in i 



comple- be complementary to each other; that is to say, shall make 

 Tiientaries. ^j^j^e ^y^gQ combined. This order, according to Professor 

 Grassmann, is that of the following diagram. i 



PUEPLB. 



GREEN, 



1 See the paper already referred to. Professor Grassmann does not give 

 the circular form, but his tabular statement of the pairs of complementaries 

 comes to the same thing. The law that every colour in the spectrum has 

 its complementary in the spectrum was deduced by Professor Grassmann 

 from theoretical considerations ; and it has been to a great extent con- 

 firmed by the experiments of Helmholtz, who " found that the colours from 

 red to green- yellow were complementary to colours ranging from green-blue 

 to violet, and that the colours between green-yellow and green-blue have no 

 homogeneous complementaries, but must be neutralized by mixtui-es of red 

 and violet. " (Professor Clark Maxwell on the Theory of Compound Colours, 

 Philosophical Transactions for 1860.) I think there can be little doubt 



