Termanent Colours of Opake Bodies. 267 



afts upon light, by tranfmi/Tion only, it is evident 

 that bodies do not appear coloured either by 

 reflecting, or emitting the rays. 



I have not attended to any other hypothefis* 

 which are unfupported by experiments. 



Sir Ifaac Newton, and, I believe, all later phi- 

 lofophers, except M. Euler, have attributed to 

 colouring matter a reflecftive power. And the 

 artifts, whofe vi'orks depend upon the preparation, 

 and ufe of colouring materials, feem, in general, 

 to have adopted the fame theory. 



As an inftance of this agreement, I have cited, 

 from M. Hellot, one of the mod fkilful and in- 

 telligent authors, who have treated of the Art of 

 Dying, a paflage which comprizes his opinion 

 refpeding the adlion of the tinging particles on 

 the rays of light.* 



All the other writers, on the fame fubjedt, 

 appear to agree in that eftablifhed opinion : but, 



• " Hellot. Art de la Teinture des Laines. 1772, 

 p. 117, Nous ne connoiflbns, jufqu' a prcfent, que deu3(- 

 plantes, qui donnent le bleu, aprcs leur preparation ; 

 I'une eft IMfatis ou Glaftum, qu'on nomme Paftel en 

 Languedoc, et Vouede en Normandie; leur preparatioa 

 Coniille dans la fermentation continuee prefque jufqu' a 

 la putrefaftion de toutes les parties de la plante, la racine 

 exceptce ; par confequent, dans un developpement de tous 

 leurs principes, dans une nouvelle combinaifon es arrange- 

 ment de ces mcmes principes, d'oii il refulte un affem -• 

 blage de particules infiniment deliees, qui, appliquces fur 

 un fujet quelconque, y refiichijfent la lumiere bien difFcrem- 

 mentde ce qu' elles feroient, fi ces memes particules etoicnt 

 «ncore jointes u celles que la fermentation eo a fepaiees." 



they 



