14 MR. J. SMITH ON THE ORIGIN OF COLOUR 



me much like arguing in a circle^ always ending where 

 you began, and, without knowing it, starting again on 

 the same track. One of the most elegant writers on 

 physics we have says : " This solar spectrum, as it is 

 called, formed upon the wall, consists, when the light 

 is admitted by a narrow horizontal slit, of four coloured 

 patches corresponding to the slit, and appearing in the 

 order from the bottom of red, green, blue and violet. 

 If the slit be then made a little wider, the patches at 

 their edges overlap each other, and, as a painter would 

 say, produce by the mixture of their elementary colours 

 various new tints. Then the spectrum consists of the 

 seven colours commonly enumerated and seen in the 

 rainbow, viz., red, orange, yellow, green, blue, indigo and 

 violet. Had red, yellow, blue and violet been the four 

 colours obtained in the first experiment, the occurrence of 

 others, viz., of the orange from the mixture of the red and 

 yellow, of the green from the mixture of the yellow and 

 blue, and of the indigo from the mixture of blue and the 

 violet, would have been anticipated. But the true facts of 

 the case not being such proves that they are not yet under- 

 stood." He adds : " No good explanation has been given 

 of the singular fact of refraction."* Why then constantly 

 appeal to the phenomena of the prism, when so little satis- 

 factory is known about it ? The most obvious method of 

 procedure is to inquire in such cases of nature in her 

 ordinary moods, how she performs such and such opera- 

 tions; to inquire how colours are usually produced, and if 

 there are any simple processes which can be explained and 

 received as data for future investigation. 



23. Adopting this method of investigation, the first 

 inquiry which suggest itself is. 



What is Blue? 



* Dr. Arnott's Mements of Fhysics. 



