112 



CONSIDERATIONS ON COLOURS. 



IX. 



Abjlracl of a Memoir, entitled Confederations on Colours, and 

 feveral of their fingular Appearances; read at the Clafs of 

 Mathematical and Phyfical Sciences of the National Jnjlitute, 

 March, IS05, by C. A. Prieur *. 



Object of the 

 memoir. 



Begins with the 

 coiouis refus- 

 ing from a mix- 

 ture of rays. 



For which we 

 are indebted to 

 Newton. 



Preliminary re- 

 quisites. 



Complementary 

 colours. 



VJ'LJR author here endeavours to account for feveral pheno- 

 mena, which appear to him never yet to have been properly 

 explained : or rather im% his object to exhibit a general theory, 

 by means of which all cafes of coloured appearances, even the 

 moft extraordinary, may be referred to certain principles. 



He lets out from the known opinions concerning the various 

 Ipecies of luminous rays, the colours refuliing from a mixture 

 of feveral of thefe rays taken at different parts of the folar 

 Ipectrum, and among others the very remarkable cafe, where 

 (he rays are fo chofen, that their union produces on the organ 

 of fight the fenfation of whitenefs, even if two forts of rays 

 only be employed. ^ 



For thefe ideas we are indebted to the difcoveries of the 

 immortal Newton, and they flow immediately from the me- 

 thod he has propofed for determining what colour would be 

 obtained from a mixture of certain quantities of other given 

 colours. 



If we would thoroughly comprehend what pafTes in the 

 feeing of colours, it is indifpenfable in the firfl place to obtain 

 a familiar acquaintance .with the (hades comppfed of feveraf 

 iimple rays; to acquire precife ideas of black and of white, 

 and of the complication thefe introduce into coloured appear- 

 ances ; and more efpecially to underiland the relation of co- 

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

 capable of forming by their union ,white, or if you pleafe any 

 other compound lint. 



Two colours having this kind of relation to each other are 

 reciprocally termed amiplementary colours: one of thefe being 

 given, the other may be determined with more or lefs preciiion 

 by various modes of experiment, calculation, or fimple reason- 

 ing; and the confederation of them applies very ufefully to a 

 great number of cafes, as will be feen farther on. 



* Tranflated from the Annales de Cbiinicy Vol. LIV. p. 5, April, 

 180j. 



3 We 



