U'ke7i reduced into tJiin Pellicles. 335 



The coronse we sometimes see surrounding the sun and the 

 moon, are probably phaenomena of the same kind. 



In another place Newton speaks of undulated folds, like 

 those of an eel, which he supposes to be produced in the 

 rays, when they pass by the edges and sides of bodies *. I 

 think I can explain the formation of these folds, and the ne- 

 cessity for their existence. 



With this view, I shall call the attention of my readers to 

 the very interesting results of the experiments of Newton 

 and S. Gravesande, relative to inflexion : results so certain, 

 that surely no philosopher can raise any doubts against 

 them ; but it is nevertheless satisfactory to be able to prove 

 them ourselves, and to seize upon them with all their pecu- 

 liarities, as I had the advantage of doing in some experi- 

 ments upon this very subject made at the house of M. Tre- 

 mery, in concert with Messrs. Berthollet, sen, and jun. 

 These experiments I have detailed in a former part of my 

 work. 



From the action exercised upon the luminous rays by a 

 point or by the edge of any given body, we are, in my opi- 

 nion, warranted in considering each molecule or parcel of 

 isolated matter as enveloped with a double sphere of activity 

 relatively to the light ; the one more interior, where the 

 rays are attracted by the body, the other more exterior, 

 where the rays are repelled. But it will happen, in several 

 positions, that a ray coming to traverse the repulsive sphere, 

 will therein describe a convex curve on the side of the body, 

 that if it afterwards intersects the attractive sphere, the 

 curve of deviation will then be concave with respect to the 

 body, and that it will become a second time convex when 

 the ray re-passes into the sphere of repulsion in order to 

 continue its route. Here then is the covnnipncenient of the 

 snaky movement, the folds of which may be multiplied by 

 a string of molecules. 



Will this cause be sufficient for operating the access of 

 easy reflexions and transmissions of rays directed upon the 

 Kurlace of bodies ? 



The phsenomena of colours, which we are here discussing, 



• Optics, book iii. question 3. 



seem - 



