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I^ONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 

 JOURNAL OF SCIENtfE. 



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^}y^^j^2i^ NOVEMBER 1856. :^::^£': 



Xil. -^4 Theory of the Composition of Colours on the Hypothesis 

 o «' of Undulations. 5?/ Professor Challis*. 



.T> ECENT experiments have added largely to the class of facts 

 AV that relate to the composition of colours, but nothing, as 

 far as I am aware, has been done towards explaining the facts 

 by any theory of light. The undulatory theory, if it be true, 

 must admit of this application. In a communication to the 

 British Association, published in the Report of 1834 (p. 544), 

 I gave explanations in accordance with that theory of some facts 

 relating to the composition of the colours of the spectrum, so far 

 as to establish a presumption that an analogy exists between the 

 composition of colours and the composition of small vibrations. T* > x ^ 



^his subject I propose now to recur. 



There is a peculiarity about the class of facts to be explained 

 which must first be noticed. Colour is a sensation, not a mate- 

 rial existence. It is, however, certain that corresponding to every 

 sensation of colour there must be definite physical circumstances. 

 But experiment has proved that when the external circumstances 

 are the same, the sensations are not always the same in diff"erent 

 individuals. The difiierence consists for the most part in the 

 absence in some of sensations perceived by the majority, as in J 



cases of colour-blindness. Admitting, for the moment, the truth i p; 

 of the undulatory hypothesis of light, the undulations of the J; 



sether may be conceived to excite in the nerves of the eye vibra- |^ 



tions which in general correspond to the exciting undulations, 3 



but, owing to peculiarity of organization, may in some cases r:f 1 g, 

 deviate from this normal character ; for it cannot be imagined 



* Communicated by the Author. 

 Phil Mag. S, 4. Vol. 12. No. 80. Nov, 1856. Z 



