on COLOURS OF THIN PELLICLES. 131 



■when they pass very near bodies*. The formation of these, 

 and the necessity of their existence, I think I can render 

 sensible. 



With this view I would call tlie attention to the very in- "^°J^/J^^'^ '"'^ 

 teresting results of the experiments of Newton and s'Grave- 

 sande relative to inflexion: results so certain, that no one 

 certainly will attempt to question them, but which it is not- 

 Avithstanding satisfactory to be able to verify ourselves, and 

 to observe with ail their peculiarities, as I had the advan- 

 tage of doing in experiments on the same subject made at 

 Mr. Treraery's, in concert with Messrs. Berthollet, and the 

 particulars of which I have given in a preceding part of my 

 work. 



From the action which a point, or the edge of any body, E/^h particle 



^ . " , of matter sur- 



exerts on the luminous rays, it seems to me we are author- rounded by an 



ized to consider eacli molecule, or distinct parcel of matter, attractive 

 as enveloped with a double sphere of activity in respect to j^ and'arepul- 

 light: one more interior, in which the rays are attracted by sive sphere ex- 

 the body; the other more exterior, in which the rays are re- 

 pelled. Now it will happen, that, in several positions, a 

 ray, coming to traverse the repellent sphere, will describe: 

 there a curve convex toward the body; that, if it afterward 

 penetrate the attractive sphere, the curve of deviation will 

 be concave toward the body ; and that it will a second time 

 become convex toward it, when the ray repasses into the 

 sphere of repulsion, to continue its course. Here we have 

 the commencement of an undulatory motion, the curves of 

 which may be multiplied by a series of molecules. 



., Would this cause be sufficient, to effect the fits of easy Is this the cause 

 reflection and transmission of the rays directed to the sur- ^^^y refle'ction 



face of a body.!* &transmi,sion? 



The phenomena of colouration here considered appear to Probably it is. 

 tne, to be very naturally explained by this simple mean: 

 yet I merely announce it as a probability. To leave no- 

 thing to be desired in such a proposition, no doubt more 

 profound investigation is necesi«ary ; as well as in particular 

 to put it to the test of calculation, in order to see, whether 

 it be possible by the attractive and repulsive powers ascribed 



* Opt. lib, 5, qusst.. 3. 



K 2 to 



