Internal Prismatic Reflexion. 

 Fig. 1.* 



357 



(«) 



vl9 



rl6 



rl3 



r-10 



r4 



|;'4 



r*l3 



r'16 

 r-19 



C^') 



r-4 



r-13 

 r-16 



«-19 

 r-10 



g.4 



vl3 



rl6 



D*4 



t;-7 



r'l9 



v'13 



wl9 



wis 



V.7 



r.l6 



G 



R 



10 



r'7 



r.l3 

 ^.4 



v4 

 rl9 



vlO 



V.16 



I next traced all those three spectra to a distance from 

 the prism equal to six times the breadth of its face, and 

 fig. 2 will give an idea of the great difference which this 

 short distance would make in the nature of the spectra. 

 Fig. 1 {a) and fig. 2 («) are the same spectrum at two 

 different distances, one close to the prism, and the other a 

 few inches from it ; so likewise are fig. 1 {h) and fig. 2 (J), 

 as are also fig. 1 (c) and fig. 2 (c) : fig. 2 is reduced to save 



* Fig. 1 represents tlie comparative length and chromatic distribution of the 

 spectra immediately on leaving the prism ; v, r, g, denote the colours violet, red, 

 green ; (the capitals V, R, G, being the primary or direct rays) ; and the numbers 

 denote the number of reflexions which have preceded each individual emersion : 

 ia some few points two emersions coincide. 



