2i6 Mr. Delaval on the Caiije of the 



Coloured. When it is viewed by incident Hghf, 

 it exhibits a Blue Tinge. The yellow, or orange 

 colour arifes from the tranfmifTion of the lefs re- 

 frangible raysj from whofe mixture that colour 

 refults. The more refrangible rays are not tranf- 

 mitted through the glafs, but are reflefted by the 

 white particles, and pafs back through the Tranf- 

 parent Medium, which is between thofe particles 

 and the anterior furface of the glafs. 



I fhall here cite from Sir Ifaac Newton, a paf- 

 fage, * from which it appears, that from the mix- 

 ture of thofe rays, which are tranfmitted, a yel- 

 low, or orange colour muft be produced ; and 

 that thofe rays which were intercepted, and re- 

 flefted, muft eompofe a blue colour. 



As the arfenical particles are equably diffufed 

 throughout the glafs, with which they are com- 

 bined, 



• The letters R, and f, refer to a figure in Sir Ifaac 

 Newton's Optics (L. I. Part. II. Prop. VIII. Probl. III.) 

 which reprefents the rays of light, call on a white paper 

 after they have been refrafted through a prifm, and ex- 

 preffes the compound colours wl ich refult from the feveral 

 mixtures of the differently refrangible rays. The follow- 

 ing extracts relate to fuch mixtures of the rays, as produce 

 blue, and orange colours. 



•• At R, where the violet-making, indigo-making, 

 *♦ blue-making, and one half of the green-making rays 

 •' are mixed, their colours muft compound a middle c©- 

 " lour between indigo and blue. 



" At f, the mixture of red, orange, yellow, and one half 

 •' of the green, muft compound a middle colour between 

 .«« orange and yellow." 



