135 



the same variety of colour occurring at eacli end of the 

 prismatic spectrum. The strict order in which the pure 

 and mixed coloured rays present themselves is as 

 follows : 



1. The extreme red: a ray which can only be dis- 

 covered when the eye is protected from the glare of the 

 other rays by a cobalt blue glass, is of a crimson 

 character a mixture of the red and the blue, red 

 predominating.* 



2. The red : the first ray visible under ordinary cir- 

 cumstances. 



3. The orange : red passing into and combining with 

 yellow. 



4. The yellow : the most intensely luminous of the 

 rays. 



5. The green : the yellow passing into and blending 

 with the blue. 



6. The blue: in which the light very rapidly di- 

 minishes. 



7. The indigo : the dark intensity of blue. 



8. The violet : the blue mingled again with the red 

 blue being in excess. 



9. The lavender grey : a neutral tint, produced by 

 the combination of the red, blue, and yellow rays, which 

 is discovered most easily when the spectrum is thrown 

 upon a sheet of turmeric paper, 



10. The fluorescent rays : which are either a pure 

 silvery blue or a delicate green. 



Newton regarded the spectrum as consisting of seven 

 colours of definite and unvarying refrangibility. Brews- 

 ter and others appear to have detected a great diffusion 



* Herschel, On the Action of Crystallized Bodies on Homo- 

 geneous Light, and on the causes of the deviation from Newton's scale 

 in the tints which many of them develope on exposure to a polarized 

 ray. Phil. Trans., vol. ex., p. 88. 



