Permanent Colours of Opake Bcdies. 255 



When the rays accede to the opake particles 

 of femipellucid fubftance?, fome forts of them 

 are refiefled back, from the anterio. furface of 

 thofe particles : the other forts of rays, which arc 

 not reflefted back, art diverted from the dircflion 

 which is oppofite to the anterior furface of the 

 opake particles, and, pafTing through the inter- 

 vals, between the particles, are tranfmitted 

 throug;h the mafs. 



When the rays are incident upon the particles 

 of Tranfparent Coloured Bodies, none of them 

 arereflefted back, becaufe the colouring particles 

 are not endued with any refleftive power. But, 

 fome of the rays are either ftopt at the anterior 

 furfaces of the particles, or are diverted into fuch 

 diredions, as render them incapable of pafllng to- 

 wards the farther fide of the mafs, and, confe- 

 quently fuch rays cannot be tranfmitted. The 

 rays, which are not thus intercepted, or difperfed, 

 are tranfmitted, in the fame manner as thofe 

 which pafs through femipellucid media. 



Thus it is evident, that the coloured rays, which 

 are tranfmitted through femipellucid fubftances 

 are infle^ed by the Opake Particles : and thofe 

 which are Tranfmitted through Tranfparent Co- 

 loured Subftances, are infie^led by the colouring 

 particles. 



I have already fliewn, that thofe media tranfmit 

 coloured light with the greateft ftrength, which 

 have the greateft rcfradtive power. From the 



preceding 



