24 ART. 3. AICHT AND TAN AK A DATE : THEORY OF 



9. Colours of the rainbow. 



Pernter calculated the colours of the rainbow due to the 

 sun, but his calculation was not sufficient to establish the above- 

 mentioned results. We repeated the calculation for two cases. 

 The theory of compound colours being the subject of much 

 dispute, there is as yet no settled opinion. But we can admit 

 that, excluding the physiological and psychological points of 

 view, there are three primary colours, as Maxwell's experiment-^^ 

 shows. For the discussion of the colours of the rainbow, we 

 may conveniently take only these three primary colours, in 

 such a ratio as to produce white, and proceed in the manner 

 indicated by Maxwell. 



We take the primary colours 



; = 6302 X 10-' cm. .">211 x 10"'^ cm. 4G.59 x 10-' cm. 



(Scarlet) (Green) (Blue) 



corresponding to Maxwell's 



[24] [46] [64] 



in the ratio 1 : 1.62 : 1.60, so as to produce white, 

 and «=1.332 1.335 1.339 



whence D=42°22 41°80 41°21 



and for r= 0.025 cm. 



x = 115.3 131.6 142.9 



for r = 0.05 cm. 



z= 183.0 209.0 226.9 



Thus we obtain the values of F given by Table II and 

 Table III in the preceding article. The results of compound 

 colours represented by Pi. II PI. V, PI. II and PI. IV 



(Ij Scientilic Papers, I. p. 410 (Cambridge, 189 J). 



