Colour -combinations by Polarized Light. 14? 



Complementary Colours. 

 Red, Green-blue ; 



Orange, Cyanic blue ; 



Yellow, Indigo-blue. 



Yellow-green, Violet. 



"When in one spectrum the band enters the green, in the other a 

 band will be seen on the outer margin of the red and a second at 

 the opposite end of the violet — showing that to the green there 

 does not correspond one complementary colour, but a mixture of 

 violet and red, i. e. a reddish purple. 



Combination of two Colours. — Next as to the combination of two 

 parts of the spectrum, or of the tints which represent those parts. 

 If, in addition to the apparatus described above, we use a second 

 quartz plate, Q, and a second double-image prism, V v we shall form 

 four images, say O O, O E, E O, E E ; and if A, A' be the com- 

 plementary tints extinguished by the first combination Q P alone, 

 and B, B' those extinguished by the second Q x P x alone, then it will 

 be found that the following pairs of tints are extinguished in the 

 various images: — 



Image. 



Tints extinguished, 



00 



B,A, 



OE 



B', A', 



EO 



B',A, 



EE 



B, A'. 



It is to be noticed that in the image O E the combination Q x V x 

 has extinguished the tint B' instead of B, because the vibrations 

 in the image E were perpendicular to those in the image O formed 

 by the combination Q P. A similar remark applies to the image E E. 



The total number of tints which can be produced by this double 

 combination Q P, Q x P x is as follows : — 



4 single images^ 

 6 overlaps of two, 

 4 overlaps of three, 

 1 overlap of four. 



Total.. 15 



Collateral Combinations. — The tints extinguished in the overlap 

 O 0+E O will be B, A, B', A; but since B and B' are complemen- 

 tary, their suppression will not affect the resulting tint except as 

 to intensity, and the overlap will be effectively deprived of A alone ; 

 in other words, it will be of the same tint as the image O would 

 be if the combination Q 1 P x were removed. Similarly the overlap 

 O E-f EE will be deprived effectually of A' alone ; in other words, 

 it will be of the same tint as E, if Q T P T were removed. If therefore 



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