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XLIII. Extract from a Memoir entitled " Considerations 

 on Colours, and several of their singular Appearances." 

 Bead in the Mathematical and Physical Class of the 

 French National Institute, Fentose 13, An 13. By 

 C. A. Pkieur*. 



JL HE author of lliis memoir endeavours to account for 

 several phasnoinena which appear to him not to have heen 

 before properly explained : or, rather, his object is to give 

 a general theory, by the help of which ail the cases of co- 

 loured appearances, and even the most singular, may be 

 referred to certain principles. 



He sets out from known opinions in regard to the diffe- 

 rent kinds of luminous rays; on the mixture resulting from 

 several of these rays taken at different places of the solar 

 spectrum, and among others on that very remarkable case 

 when the rays are so chosen that their union produces on 

 the organ of sight the sensation of whiteness, even if two 

 kinds of rays only be employed. 



For these ideas we arc indebted to the discoveries of the 

 immortal Newton ; and they flow immediately from the 

 method which he proposed for determining what colour 

 will be obtained from the mixture of any given quantities 

 of other colours. 



If we are desirous of comprehending fully what takes 

 place in the vision of colours, it is first indispensably ne- 

 cessary that we should be familiarised with knowing the 

 shark's composed of different simple rays, and with forming 

 correct ideas of black and white, and the complication which 

 they produce in coloured appearances ; and in particular to 

 make ourselves acquainted with the correspondence of co- 

 lours, which, taken two and two in a certain order, are sus- 

 ceptible (^f forming, by their union, white or any other 

 complex shade at pleasure. 



Two colours which have this kind of relation are called 

 compleynuitury colours ; one of them being given, the de- 

 tcrmlnatiuu of the other may be made, with more or less 

 precision, bv experience, calculation, or mere reasoning ; 

 aiul the consideration of them may be applied with much 

 utility to a great number of cases, as will be seen hereafter. 



Several details are here eivcn, which those versed in 

 optics, or habitnallv acquainied v.ith the mixture of co- 

 lours, may rcadilv supply : besides, the rest of the uie- 



• From the Jmirvfil ilr Chinile, No. ICO. 



Vol.. C2. No. 68. Sept. 1905. T molv. 



