SI (J On the Decomposition of Light. 



aminoniacal solution of copper, in a pbial witb pknc 

 parallel surfaces : for the green a solution of muriat of 

 copper, in a similar phial : and for the red, either wine of 

 a good colour, or a tincture of cochineal. Ali these nnist 

 be sufficiently concentrated, or ihcy will transmit other 

 ravs, besides those v\e have in view. This concentration 

 has the inconvenience of rendering the colour obscure, it is 

 true, and this is some obstacle to their use; but it is the 

 only way in which nature permits us to obtain simple 

 colours, and we must be content with it. 



Coloured glasses might be substituted for the red and 

 green liquors; but with respect to the violet I could not 

 procure any, on which I could depend. 



Every thing being thus prepared, I made my experiments 

 in concert with Mr. Tremery and Mr. Drappier. 



We had a screen , which we could place at will before 

 the cloth opposite the place of the spectrum. In this screen 

 was a small circular hole 3 or 4 milliinetres (I. 17 or I. 56 

 line) in diameter, by means of which we could allow a 

 small coloured pencil to fall on the cloth, while all the rest 

 was dark. We could easily ascertain, that this little pencil, 

 taken successively from the different colours, was simplified 

 as much as possible by refraction; for the circular spot, 

 examined some distance with a prism, was not at all ir- 

 regular. 



We then passed through the small hole a pencil of very 

 decided blue ; and in this respect our latitude of choice was 

 great, since in our spectrum the blue had an extent of more 

 than 54 millimetres (2 inches). The blue spot being well 

 formed on the cloth, the green phial was placed before the 

 hole; when the ligbl of the spot was inmiediately much 

 weakened, and its colour changed to green. On substituting 

 the violet phiiil in the place of the green, the spot became 

 violet. This experiment was repeated several times, that 

 we might convince ourselves of the fact, and succeeded 

 uniformly. 



The trial with the yellow succeeded in like manner; it 

 was changed successively to red and green, according to the 

 substance opposed to the rays. 



Another 



