RESEARCHES BASED UPON THE THEORY 269 



the Rayleigh mixture. These experiments, however, require confirma- 

 tion by more trustworthy methods of heterochromatic photometry. 



Whilst the researches of Hering and his school have contributed 

 many facts of value to our knowledge of colour vision, especially in 

 the domain of induction, one cannot help being struck by the fact that 

 they have led to far-reaching modifications and increased complexity 

 in the theory itself. 



